Soumya Ranjan Panda

Sebastien Fregonese

Marina Deng

Anjan Chakravorty

Thomas Zimmer

TCAD and EM Co-Simulation Method to Verify SiGe HBT Measurements up to 500 GHz

Keywords: SiGe HBT, HF S -parameter measurement, on-wafer, TRL calibration, de-embedding, TCAD-EM co-simulation, Virtual measurement

A systematic method for the verification of high frequency measurement (up-to 500 GHz) of silicon germanium heterojunction bipolar transistor (SiGe HBT) is proposed. First of all, the method involves an accurate estimation of the effects of passive environment on the overall measurement by a detailed electro-magnetic (EM) simulation. This ensures that the complete measurement environment like probes, pads and access lines along with the appropriate layouts are precisely included in the EM simulation framework. In order to additionally include the active device like S iGe HBTs, technology computer aided design (TCAD) tool is used to simulate the device S -parameters. TCAD simulation results are fed into an EM-plus-SPICE simulation framework to emulate a complete on-wafer measurement environment. The final simulation results show appreciable correlation with the on-wafer measurement data up-to 500 GHz.

Introduction

A reliable circuit design requires accurate compact model of devices to be deployed in VLSI tools. The physics-based models that are used in VLSI tools are highly dependent on accurate DC and RF characterization. Hence it is important to understand the Sparameter characterization in high frequency range and verify the models in VLSI tools in that range. But the characterization above 110 GHz is still a challenge and there is no established de-embedding method above this range [START_REF] Yau | Device and ic characterization above 100 ghz[END_REF]. In fact, a very few research groups have published S -parameter measurement results above 110 GHz [START_REF] Williams | Calibrations for millimeter-wave silicon transistor characterization[END_REF] [3] [4] [START_REF] Galatro | Capacitively loaded inverted cpws for distributed trl-based de-embedding at (sub) mm-waves[END_REF] [START_REF] Deng | Small-signal characterization and modelling of 55 nm sige bicmos hbt up to 325 ghz[END_REF].

High frequency measurements require careful calibration procedures. Off-wafer calibration is more popular in the production environment [START_REF] Deng | Small-signal characterization and modelling of 55 nm sige bicmos hbt up to 325 ghz[END_REF]. However, since the calibration substrate is different from that of the desired wafer to be characterized, the off-wafer calibration leads to systematic errors, which is correlated to different probe-to-substrate electromagnetic coupling [START_REF] Galatro | Millimeter-wave on-wafer trl calibration employing 3-d em simulation-based characteristic impedance extraction[END_REF] [START_REF] Seelmann-Eggebert | On the accurate measurement and calibration of s-parameters for millimeter wavelengths and beyond[END_REF]. Similarly, as different probes are used to measure different frequency bands, discontinuity appears in the measured data due to change in RF probes if the probe's cross-talk is not fully corrected by the calibration procedure. A detailed explanation of the work has been reported in [START_REF] Seelmann-Eggebert | On the accurate measurement and calibration of s-parameters for millimeter wavelengths and beyond[END_REF].

On-wafer calibration is a better choice for high frequency (HF) measurement because it avoids some of the above mentioned limitations observed in off-wafer calibration. Thru-Reflect-Line (TRL) calibration algorithm is the method of choice [START_REF] Williams | Calibrations for millimeter-wave silicon transistor characterization[END_REF] since it provide a welldefined reference plane and does only require a low knowledge of the standards (geometrical dimensions and characteristic impedance extraction), that indeed gives a better accuracy in the high frequency domain. Nevertheless, this method is not the good choice for the 1 lower frequency since it would requires extremely long lines and SOLT/LRM method are more suitable in this low range of frequency. But while probing the Thru and Line, it is necessary to shift one probe which may add errors in the measurement particularly in case of manual probe stations [START_REF] Fregonese | On-wafer characterization of silicon transistors up to 500 ghz and analysis of measurement discontinuities between the frequency bands[END_REF] [START_REF] Sakamaki | Uncertainty analysis method including influence of probe alignment on on-wafer calibration process[END_REF]. The drawback of the on-wafer calibration is the need for a specific design of test structure which can be time-consuming. This design requires engineering effort and expertise. For example, the line lengths need to be chosen properly to cover the required frequency band; the geometry of the line needs to minimize the loss and allow only one mode to propagate; the design of the pad itself needs to be optimized to limit the probeto-substrate coupling; the pad-to-pad distance needs to be sufficiently long in order to ensure a reduced crosstalk and finally one has to keep enough space between the structures to avoid coupling [START_REF] Seelmann-Eggebert | On the accurate measurement and calibration of s-parameters for millimeter wavelengths and beyond[END_REF][10] [START_REF] Phung | Influence of microwave probes on calibrated on-wafer measurements[END_REF].

In order to check the trend, consistency and accuracy of the high frequency measurement results, one has to compare the data with those obtained from calibrated simulation. One can think of options like TCAD simulation or electrical compact model simulation for this purpose. We have chosen TCAD simulation as reference in this work. In this paper, using Sentaurus TCAD and Ansys-HFSS electro-magnetic (EM) simulations, we explore and verify the high frequency measurements of SiGe HBTs. As a motivation for such an investigation, Fig. 1 (a) and (b) compares the measurement and calibrated TCAD simulation of frequency-dependent Sparameters corresponding to a SiGe HBT from ST Microelectronics B55 technology at a particular bias in the main operating regime, and to highlight the deviations magnitude of S 22 is plotted w.r.t bias variation in Fig. 1 (c). It is observed that in the lower frequency range (below 110 GHz), the measurement and simulation are in good agreement. However, some discontinuities are observed in the measurement data at the cross-over points (110 GHz, 220 GHz and 325 GHz) 2 of different frequency bands. Also the characteristics in the upper frequency range tend to deflect from the TCAD simulations. This motivates us to emulate a more realistic measurement environment. To do so, we combine our TCAD simulation results with EM simulation that includes the back-end-of-line (BEOL) along with the probes. This TCAD plus EM simulation data together will be henceforth called as Virtual measurement throughout the paper. After that, we follow all the on-wafer calibration and de-embedding procedures on this virtual measurement data. Finally for verification, both TCAD and de-embedded virtual measurement data are compared with actual measurement results.

Section 2 of this paper provides a comprehensive discussion on the calibration of TCAD simulation. In section 3, a brief description of the measurement setup and procedures are provided. The methodology of combining TCAD and EM simulation to produce virtual measurement results is explained in section 4. Finally, we conclude in section 5.

TCAD Simulation Setup and Calibration

In commercially available Sentaurus TCAD simulator an SiGe-HBT structure corresponding to ST Microelectronics's B55 process is developed as shown in Fig. 2. All the dimensions including the shallow and deep trench isolation are ensured to be closely identical with those of the B55 process during the device design. The doping profiles have been reproduced using analytic mathematical models as shown in Fig. 3 [12] [START_REF] Sentaurus | Manuals, synopsys inc[END_REF]. All necessary physical effects are taken into account in the simulation using appropriate models and parameter sets are appropriately tuned from Monte Carlo simulation as discussed below [START_REF] Bufler | Full-band Monte Carlo simulation of electrons and holes in strained Si and SiGe[END_REF] [START_REF] Panda | Tcad simulation and assessment of anomalous deflection in measured s-parameters of sige hbts in thz range[END_REF]. For the carrier transport, we have used hydrodynamic model that solves drift-diffusion equations along with the additional energy balance equations for minority carriers. The Slootboom bandgap narrowing model with appropriately tuned N re f value is used to account for the effect of carrier concentration at heavy doping [START_REF] Van-Tuan | Tcad calibration of high-speed si/sige hbts in 55-nm bicmos[END_REF]. Parameter in the Caughey-Thomas model has also been tuned as suggested in [START_REF] Van-Tuan | Tcad calibration of high-speed si/sige hbts in 55-nm bicmos[END_REF]. Shockley-Read-Hall and Auger recombination models are used to take care of the recombination effects and Lackner's model has been considered to include the effect of breakdown at high electric field.

The base-emitter and base-collector junction capacitances, shown in Figs. 4(a) and (b) respectively, are obtained from simulation at low-frequency and are matched with the corresponding measured data to validate the approximation used to emulate the doping profile in TCAD [START_REF] Korn | Experimental verification of tcad simulation for high-performance sige hbts[END_REF]. A maximum permissible error of 3 0.5 fF is allowed while fitting the capacitances. The recombination parameter in poly-silicon emitter has been tuned to match the base current. A more ideal germanium profile is considered keeping the maximum mole fraction within the permissible range. This effectively helped us in capturing the collector current in the Gummel plot as shown in Fig. 5.

Further, the TCAD simulated transit ( f T ) and maximum oscillation frequencies ( f max ) are compared with the measured data at V CB =0 V and T=294 K in Figs. 6(a) and (b), respectively, prior to carry out the S -parameter comparison [18]. It is to be noted that for the f T and f max extraction, a spot frequency at 63 GHz has been chosen [START_REF] Haugerud | Proton and gamma radiation effects in a new first-generation sige hbt technology[END_REF].

Since the Gummel (Fig. 4) and f T characteristics (Fig. 6(a)) show high level of correlation between the TCAD and measured data and since these two characteristics are highly dependent on the intrinsic part of the HBT, one can conclude that a reasonably accurate calibration of the 1D profile of the device has been obtained in TCAD [START_REF] Taur | Fundamentals of modern VLSI devices[END_REF]. Since f max is dependent on f T and other external parameters such as base resistance and basecollector and collector-substrate capacitances, the high level of agreement between the TCAD and measured f max characteristics ensures that the profile parameters related to the extrinsic base, buried layer in the collector region and the substrate doping at its contact and around the deep trenches are closely identical with those of the B55 process. The same is also confirmed from S 22 parameter shown in Fig. 1 (c). This is also validated after looking into the doping profiles received from ST Microelectronics (not disclosed here due to intellectual properties agreements).

Actual Measurement Procedure

We have carried out the S -parameter measurements up-to 500 GHz for V BE varying from 0.7 V to 1 V and V BC =0V. In order to measure from 1 GHz to 500 GHz, four different measurement benches such as (i) Agilent's E8361A VNA up to 110 GHz using extenders (N5260-60003) above 67 GHz (ii) 140-220 GHz (iii) 220-330 GHz and (iv) 325-500 GHz bands with a four-4 port Rohde & Schwarz ZVA24 VNA coupled with extenders (ZC220-ZC330-ZC500) have been used. The power level is set to approximately -32 dBm using a calibration table provided by extender supplier in the four bands for measurement of both active and passive elements (the latter are used for de-embedding purposes). Picoprobe RF probes with 50 µm pitch are used for covering the bands above 110 GHz and 100 µm pitch probes are used below 110 GHz. On-wafer TRL calibration and standard Short-Open de-embedding has been performed. The reference plane of the TRL is set at the top metal and at sufficiently close proximity of the vias. In the subsequent de-embedding step, which can be performed according to the well-known "lumped element" approach, only the via stack has to be removed.

Virtual Measurements, Results and Discussion

As discussed in section 1, after observing a mismatch between the actual measurement data for S -parameters with calibrated TCAD simulation, we decided to include the non-ideal environment factor related to BEOL, pad-parasitics, probes etc. into the TCAD simulation results via additional EM simulation. For this purpose, we performed three-dimensional (3D) EM simulations using commercially available simulator, Ansys-HFSS. The simulation layout is imported on a silicon substrate and the probes are placed approximately the way they appear during the measurement [START_REF] Yadav | Importance and requirement of frequency band spe-cific rf probes em models in sub-thz and thz measurements up to 500 ghz[END_REF]. Then, the whole structure along with the probes is covered within an air box as shown in Fig. 7. During the setup, proper care has been taken in choosing the meshing and assigning the appropriate boundary conditions for absorbing the radiation at the faces of the air box in order to emulate an infinite free space environment. Three separate probe models for each frequency band as shown in Fig. 8 are chosen and finally simulations are performed by giving input excitation at each wave-port. Together, the TCAD simulation of SiGe HBT up to Metal-1 and the EM simulation to account for the remaining non-ideal environmental factors, as described above and shown in Fig. 7, Fig. 8 & Fig. 9 generate the virtual measurement data for our further investigations. Now we compare actual measured S -parameter results with (i) TCAD simulation (of the actual device up to metal-1) and (ii) virtually measured data. Virtual measurement data are achieved following the flow graph described in Fig. 10. First, the RF probes, the pads and the BEOL down to metal 1 where the transistor is connected, are simulated with HFSS (4-port EM simulation). Next, the TCAD (2-port TCAD) and EM Frequency (GHz)

V BE =0.9V V BE =0.8V
Figure 11: Frequency dependent magnitude and phase of Sparameters at V CB =0 V and V BE = 0.8 V and 0.9 V for the SiGe HBT up to metal-1: comparison of de-embedded actual and virtual measurements with TCAD simulation.

simulation results are concatenated. This data set contains both the access (probes, pads, BEOL) as well as the actual transistor itself. The next step is to perform a calibration and de-embedding as done in real measurement. For that purpose, all TRL calibration standards are simulated with HFSS and the calibration is performed as shown in Fig. 10 [22]. Finally, the Short-Open de-embedding structures are simulated as well and the de-embedding is completed leading to the virtual measurement data. If calibration and de-embedding had been ideal, the de-embedded virtual measurement data would perfectly match with the TCAD simulation of the actual transistor. The results for the three data sets (actual measurements, TCAD simulation and vir-5 Frequency (GHz)

Figure 12: Frequency-dependent transit frequency ( f T ) and maximum oscillation frequency ( f max ) at V CB =0 V and V BE =0.8 V and 0.9 V for the SiGe HBT up to metal-1: comparison of de-embedded actual and virtual measurements with TCAD simulation.

tual measurements) are compared in Figs. 11 and12 for the magnitude and phase of S 11 , S 12 , S 21 , S 22 and f T , f max up to 500 GHz. From the comparison plots following observations are made.

• Up to 100 GHz, a good correlation can be observed for both V BE bias points and for all four Sparameters (magnitude as well as phase).

• In the frequency range of 50-100 GHz, we can observe there is a sudden reduction of f max , it can be observed from S 12 parameter which is strongly related to f max and can be attributed to cross-talk. A similar dip is observed in f T also in 50-100 GHz range can be due to minor difference in probe angle and position in both real and simulation environment. It can also be observed in magnitude of S 21 .

• When changing the frequency bands (especially at the transition into the 140 GHz to 220 GHz band), discontinuities are observed with the actual measurements while comparing with TCAD and virtual measurements. Therefore, it can be concluded that the TRL calibration along with short-Open deembedding are not able to correct the coupling with HF probes and the wafer surface accurately, for the given test-structure and the HF probes used. Also, the measurements are noisy and can be attributed to some difficulties to have a reliable contact between the probes and pads and in particular considering the small signal pad surface (40 ×25µm 2 ) and the thickness of the passsivation layer. In fact the very short tips of the WR3.4 probes and their angle does not allow to have a reliable contact on our BICMOS test structures (please note that this is not the case on calibration test structures).

• The discontinuous transition of actual measurements at 220 GHz is well predicted by the virtual measurement especially for the magnitude of S 12 -parameter. This discontinuity has already been studied in [START_REF] Yadav | Importance and requirement of frequency band spe-cific rf probes em models in sub-thz and thz measurements up to 500 ghz[END_REF]. WR5.1 (140-220 GHz) uses a technology which is closed to the probe designed for 110 GHz band while the WR3.4 (140-220 GHz) use a very different technology which is much more scaled. We have demonstrated in [START_REF] Yadav | Importance and requirement of frequency band spe-cific rf probes em models in sub-thz and thz measurements up to 500 ghz[END_REF] that the coupling with the environment is much stronger when the EM field is not confined by a highly scaled probe.

• Because of different resistance of bias tees from probe to probe there can be a change in bias current. The bump in the actual measurement data of f T characteristics (Figure 12) in 320-420 GHz range can be a due of this resistance difference.

• When going to higher frequencies beyond 400 GHz, a deviation of the expected behavior can be observed both in virtual as well as actual measurements compared to TCAD data. Even though no perfect agreement for the actual or virtual measurement data is achieved with the reference TCAD data, at least the trend is reasonably predicted. We suppose that the cross-talk is the source of this discrepancies since the magnitude of S 12 is increasing more than what is predicted by the TCAD. Please note the TRL calibration does not correct the cross-talk. The distance from pads to pads must be increased to reduce this effect. If with the picoprobe 110 GHz with 100 µm pitch the cross-talk start to influence the results above 70 GHz, using a highly scaled probe such as the picoprobe WR2.2, the cross-talk start only above 400 GHz.

This brings us to the conclusion that the calibration and de-embedding procedures are still need to be improved especially at the higher frequency bands and require further improvements in order to correct all the demonstrated errors introduced by the measurement environment. Two roads of improvement for measurement accuracy needs to be explored in parallel, one involving the design of the test structures the other one is about the design of the probes:

• On one side, the design of the test structures already uses a boundless ground plane, a large space between each structures (200 µm in X and 133 µm in Y-direction) may still be improved on the two following points: the distance from pad to pad to 6 reduce the cross-talk and the design of the pad itself which is mainly empirical. Please note that most of the improvement leads to very costly test structures.

• On the other side, The WR3.4 and WR2.2 probes are highly scaled probes which gives very reasonable results [START_REF] Yadav | Importance and requirement of frequency band spe-cific rf probes em models in sub-thz and thz measurements up to 500 ghz[END_REF] but requires much higher manufacturing cost. If one can develop similar probes design keeping the same geometry scaling but with the connector for the lower frequency band (especially 140-220 GHz), the measurement accuracy would be much improved.

Conclusion

For the first time, we analyzed a very high frequency (>110 GHz) measurement data using two finite element tools; one solving the EM equations and the other solving the semiconductor equations. The presented methodology provides one with sufficient confidence in the adopted characterization techniques and results. More precisely, it allows one to differentiate between accurate and erroneous characterizations. This work is a step forward (i) to adopt an improved characterization technique and (ii) to validate the TCAD result in high frequency aiding the modeling of non-quasi static and other high frequency effects. As a whole, the analysis outlines a prescription in order to make the researchers aware of certain precautions while designing the test structures, carrying out the process of characterization and verifying the corresponding results. The detailed methodology, if adopted, will certainly help in the accurate extraction of high-frequency compact model parameters.

Figure 1 :

 1 Figure1: Frequency-dependent (a) magnitude, (b) phase of Sparameters for the SiGe HBT corresponding to ST Microelectronics B55 process at V CB =0V and V BE =0.85V: comparison between actual measurement and TCAD simulation and in (c) magnitude S 22 is expanded with V BE variation at V CB =0V.

Figure 2 :

 2 Figure 2: TEM picture (left) of SiGe HBT and corresponding simulated TCAD structure (right).

Figure 3 :

 3 Figure 3: Vertical doping profiles: SIMS profiles of As and B doping (shown in different symbols) and corresponding analytic profile (line) incorporated in TCAD. Inset shows the Ge mole-fraction measured by EDX (symbol) and one used in TCAD (line).

Figure 4 :

 4 Figure 4: Base-emitter voltage dependent (a) base-emitter capacitance (C BE ) and (b) base-collector capacitance (C BC ): comparison between actual measurement and TCAD simulation.

Figure 5 :Figure 6 :

 56 Figure 5: Measured and TCAD simulated Gummel characteristics for 90 nm × 4.8 µm SiGe HBT at V CB =0V.

Figure 7 :

 7 Figure 7: Side view of the EM simulation setup for probes enclosed within an air-box. P1 and P2 probes are marked which are a part of 4-port EM simulation.

Figure 8 :

 8 Figure 8: Probe geometry used for different frequency bands: (a) 1-110 GHz (b) 140-220 GHz (c) 220-325 GHz.[START_REF] Yadav | Importance and requirement of frequency band spe-cific rf probes em models in sub-thz and thz measurements up to 500 ghz[END_REF]

Figure 9 :Figure 10 :

 910 Figure 9: Half structure from EM simulation (left) depicting the other two ports P3 as Base and P4 as collector, below which the active device starts. S, C, B and E in the TCAD structure (right) corresponds to Substrate, Collector, Base and Emitter contacts respectively.

Acknowledgment

This work is partly funded by the French Nouvelle-Aquitaine Authorities through the FAST project. The authors also acknowledge financial support from the EU under Project Taranto (No. 737454). The authors would like to thank ST-Microelectronics for supplying the Silicon wafer.


Martine Largeron
email: martine.largeron@parisdescartes.fr

Aerobic catalytic systems inspired by copper amine oxidases: recent developments and synthetic applications

Recent efforts to design synthetic quinone-based catalysts for the efficient aerobic oxidation of amines to imines have been inspired by copper amine oxidases (CuAOs), a family of metalloenzymes which selectively converts primary amines into aldehydes, using molecular oxygen through the cooperation of a quinone-based cofactor, 2,4,5trihydroxyphenylalanine quinone (TPQ) and a copper ion. Two distinct classes of bioinspired quinone-based catalytic systems have been developed. The first class consists of catalytic systems, which mimic the activity of CuAOs by exhibiting exquisite selectivity for primary amines. The second class is constituted by catalytic systems, which allow the expansion of the substrate scope to the oxidation of -branched primary amines and secondary amines including nitrogen heterocycles, two reaction types that natural CuAOs are not able to accomplish. These catalytic oxidative green processes can be applied to the C-H functionalization of primary amines and to the synthesis of several nitrogen-containing heterocycles.

Introduction

Copper amine oxidases (CuAOs) are ubiquitous enzymes isolated from mammals, many higher-order plants, fungi, yeasts and bacteria, which play a vital role in the physiology and pathology of mammals in controlling the metabolism of various primary monoamines, diamines and polyamines of endogenous or xenobiotic origin. 1 Interest in CuAOs has greatly increased in recent years, especially since the discovery that human vascular adhesion protein-1 (VAP-1), which regulates leucocyte trafficking and glucose transport, is a CuAO enzyme. VAP-1 has been shown to be upregulated at sites of inflammation and has been implicated in human diseases such as diabetes mellitus, congestive heart failure and liver disease. 2 So the rational design of selective inhibitors of CuAOs as potential therapeutic agents is of current interest. 3 CuAOs catalyze the selective aerobic oxidation of primary amines to aldehydes through the synergistic action of a quinone-based cofactor, 2,4,5-trihydroxyphenylalanine quinone (TPQ), and a copper ion (Scheme 1). [START_REF] Suzuki | Cofactors of amine oxidases. Copper ion and its substitution and the 2,4,5-trihydroxyphenylalanine quinone[END_REF][START_REF] Janes | [END_REF] TPQ is derived from a conserved tyrosine in a self-processing, posttranslational event that requires only copper and molecular oxygen. 3,6 Through the utilization of synthetic models of TPQ cofactors, 7 and using benzylamine as the model substrate, it has been established that TPQ promotes the conversion of a primary amine into an aldehyde through a transamination process which proceeds via two half reactions (Scheme 1): 8 a reductive half reaction in which the amine substrate RCH 2 NH 2 is oxidized to the aldehyde RCHO, leaving TPQ as a reduced aminoquinol form TPQ amq , followed by an oxidative halfreaction which corresponds to the reduction of molecular oxygen to hydrogen peroxide, with concomitant formation of TPQ imq .

Scheme 1 Transamination mechanism followed by copper amine oxidases in vivo.

Although the oxidation of the primary amine substrate is mediated by the quinone cofactor without direct involvement of the copper ion, this might play a role in orienting the TPQ ring correctly in the active site and in facilitating the reduction of O 2 to H 2 O 2 . 9 Very likely, the final step under single turnover conditions is a transimination reaction to form the Schiff base substrate without the need to regenerate TPQ. 3,8a Whereas TPQ oxidizes a wide range of primary amines, short to long-chain aliphatic mono-and diamines including arylalkylamines, 3 it fails to oxidize secondary and tertiary amines. Accordingly, 3-pyrroline derivatives have been shown to be transamination-specific mechanism-based inactivators through the formation of a stable pyrrolylated cofactor that cannot be reoxidized to the starting quinone (Scheme 2). 10 Scheme 2 Proposed pathway of CuAOs inactivation by 3pyrroline derivatives.

10 An important benefit of knowing the CuAOs mechanism is its potential application in the design of synthetic biologically inspired catalysts. The discovery of small-molecules catalysts capable of performing controlled aerobic oxidations under very mild conditions in a way reminiscent of enzyme catalysis is in constant demand by the pharmaceutical and chemical industries.

11

As a consequence, the general interest in amine oxidation chemistry 12 has stimulated efforts to discover effective quinone-based catalysts inspired by CuAOs for the aerobic oxidation of amines to imines. 13,[START_REF] Wendlandt | For a comprehensive review on quinone-catalyzed selective oxidation of organic molecules[END_REF] Imines are a very important class of compounds in chemistry that have widely been utilized as pivotal intermediates in the synthesis of fine chemicals and numerous biologically active compounds. 15 Although the enzymatic transamination mechanism is not in itself a suitable path to mimic the generation of imines, in the absence of water, the Schiff base product can undergo a direct addition of the amine substrate RCH 2 NH 2 leading to a dimeric imine condensation product RCH=NCH 2 R instead of the aldehyde (Scheme 3). 7 Recently, organic chemists have developed bioinspired quinone-based catalytic systems that utilize dioxygen or, more preferably, ambient air as the sole oxidant, with two objectives: a) to achieve sustainable aerobic amine oxidation reactions; b) to expand the scope of possible substrates. This paper aims to provide an overview on this area which developed rapidly during the last five years. It is organized around two classes of bioinspired quinone-based catalytic systems. The first class consists of catalytic systems, which mimic the activity of CuAOs by exhibiting exquisite selectivity for primary amines. The second class is constituted by catalytic systems, which allow the expansion of the substrate scope to the oxidation of -branched primary amines and secondary amines, two reaction types that natural CuAOs are not able to accomplish. The application of these green processes to the C-H functionalization of primary amines and to the synthesis of several nitrogen-containing heterocycles is also presented.

Bioinspired catalysts which exhibit the selectivity of CuAOs for primary amines

Organocatalysts

Inspired by biochemical model studies, 7b,c Wendlandt and

Stahl have developed a highly chemoselective method for the aerobic oxidative coupling of primary benzylic amines to yield homocoupled imines using the synthetic TPQ analog, 5-tertbutyl-2-hydroxy-1,4-benzoquinone Q 1 (Scheme 3). 16 High yields of imines up to 93% were obtained, in acetonitrile, at room temperature, under 1 atm of molecular oxygen, from variously substituted benzylic amines including the heterocyclic furfurylamine. As for CuAOs, secondary amines and tertiary amines were not oxidized under the same experimental conditions. The chemoselectivity for primary amines could be easily explained by a transamination process close to that reported for natural CuAOs (Scheme 3).

8 Scheme 3 Proposed ionic transamination mechanism for the aerobic oxidation of primary amines to imines catalyzed by Q 1 and other quinone-based models cofactors. 7 As shown for TPQ, the presence of the hydroxyl group at the 2-position plays a crucial role in protecting the quinone ring from ring amination and in directing nucleophilic addition of amine exclusively to the C-1 position (Scheme 3, step 1). 7a Also, the activation of the imine function for further nucleophilic attack by the amine (Scheme 3, step 3), leading to the extrusion of homocoupled imine (Scheme 3, step 4), is very Please do not adjust margins Please do not adjust margins likely provided by an intramolecular hydrogen bond between the 2-hydroxy group and the imine nitrogen, generating a highly reactive cyclic transition state (CTS). [START_REF]Similar effects of a 2-phenolic hydroxyl group on the reactivity of ketimine have been previously reported in the literature. See for example[END_REF] This activated nucleophilic attack of amine, which give an aminal intermediate (Scheme 3, step 3) would constitute a driving force for the overall transamination process thereby preventing any competitive Michael addition reaction. Aerobic oxidation of the generated aminophenol form (Scheme 3, step 4) generates the iminoquinone organocatalyst (Scheme 3, step 5), which can undergo transimination with the amine substrate (Scheme 3, step 6) and close the catalytic cycle by passing Q 1 . Interestingly, selective cross-coupling products could also be obtained by running the reaction in the presence of a second nonreactive primary amine. As shown in Scheme 4, primary amines bearing alcohol or amine functionalities underwent effective cross-coupling with benzylamine, without oxidation of the alcohol or amine fragment. Scheme 4 Q 1 -mediated aerobic cross-coupling of benzylamine with activated and non-activated primary amines.

The discovery of quinone-based catalysts has also allowed the in situ trapping of secondary imines for further reactions. Accordingly, Clift and co-workers have recently utilized the commercially available 2,6-di-tert-butyl-1,4-benzoquinone Q 2 as an organocatalyst for the preparation of -branched amines through a sequential quinone-promoted primary amine oxidation/nucleophilic addition process (Scheme 5). 18 Like Q 1 , Q 2 meets some criteria essential for acting as an efficient catalyst for amine oxidation. Especially, it is sterically encumbered to prevent conjugate addition of the amine while leaving the C-4 position accessible enough to allow condensation of the amine substrate.

As in the case of TPQ cofactor and Q 1 , -branched amines and secondary amines were not oxidized under the same experimental conditions. However, this oxidative C-H functionalization protocol could be extended to allylic amines provided higher amounts of Q 2 catalyst (20 mol%) were used. Scheme 5 Sequential Q 2 -mediated -functionalization of primary amines.

Finally, using simple organocatalysts, the amine substrate scope is limited to benzylic-type and allylic amines. 7,16,18 The oxidation of non-activated primary alkylamines, which are natural substrates for CuAOs, 19 is inherently more challenging and requires the development of cooperative catalytic sytems.

Cooperative catalytic systems

Our group has described a CuAO-like homogeneous cocatalytic system for the chemoselective oxidation of primary amines to imines at room temperature under ambient air.

20

The catalytic process combines two redox couples in a way reminiscent of other biomimetic catalytic systems: 21 the oiminoquinone organocatalyst IMQ, first discovered from electrochemical studies, 22 is the substrate-selective catalyst whereas the copper (II) salt serves as an electron-transfer mediator. The highly reactive o-iminoquinone organocatalyst IMQ is generated in situ from the corresponding oaminoquinol AMQ which can be easily synthesized in two steps from 2-nitroresorcinol. 23 The oxidation process starts with atmospheric oxygen and continues in a cascade-like manner by passing the oxidation potential of dioxygen through the copper salt (0.2 mol%) to IMQ (2mol%), which finally oxidizes the amine substrate through a transamination mechanism analogue to that reported for natural CuAOs (Scheme 6). 8 The reaction is enhanced through the participation of 1-acetyl and 2-hydroxy substituents, as they prevent the competing formation of Michael adducts. Analogous to the hydroxy groups of TPQ and Q 1 , the presence of the active 2-hydroxy substituent, which is engaged in an intramolecular hydrogen bond with the imine nitrogen to form a highly reactive Schiff base CTS, is required for the successful operation of the catalytic process. Accordingly, the analogue of AMQ, which lacks the 2-hydroxy substituent, generated an o-iminoquinone species which was devoid of catalytic efficiency. 22c In the presence of a second primary aliphatic amine, functionalized cross-coupled imines could be prepared in high yields through the transamination mechanism that leads to the homocoupled imine intermediate followed by dynamic transimination (Scheme 7). As a consequence, just one equivalent of each primary amine was sufficient to achieve exclusive formation of the cross-coupled imine product. 24 This oxidative strategy related to dynamic self-sorting chemistry has previously been used to obtain thermodynamically disfavoured products. 16,25 Unlike simple quinone-based organocatalysts, 7,16,18 IMQ was also able to oxidize non-activated primary aliphatic amines that are substrates for CuAOs enzymes. 20,22,24 Note, when compared with the direct electrochemical oxidation of nonactivated primary aliphatic amines, which occurs at high anodic potential (E > + 1.5 V vs SCE), 1.0 V was gained using IMQ as the electrocatalyst. 22d This result corroborated that, in the aerobic cooperative catalytic system Cu II /IMQ, the copper salt facilitates the aerobic oxidation of AMQ to IMQ. Although the aliphatic imines could be observed through monitoring the 1 H NMR spectrum, their instability and isomerisation into the enamine tautomer did not permit their isolation. 26 Nevertheless, the mild reaction conditions proved to be useful for trapping the scarcely stable aliphatic imines in situ for further reactions. Through acid-free tandem oxidative Diels-Alder reaction, aliphatic imines could react at room temperature as dienophile with Danishefsky's diene to form dihydro-4-pyridones 24 whereas, in the presence of oaminoanilines, they were engaged in cyclocondensation reaction to furnish Although this cooperative catalytic system was able to work under ambient air with high atom economy and was compatible with both benzylic and non-activated primary amines, the use of a commercially available quinone-based organocatalyst would offer enhanced practicality. Accordingly, Doris and co-workers have developed an effective heterogeneous co-catalytic system which uses commercially available 2,3,4-trihydroxyacetophenone (THAP) as a precursor of IMQ, in combination with a nanohybrid system (AuONT) made of gold nanoparticles assembled on polymerized polydiacetylene nanotubes. 28 Not surprisingly, this heterogeneous cooperative catalytic system behaved like the Cu II /IMQ homogeneous co-catalytic system and followed the same transamination mechanism (Scheme 6) at the exception of the first catalytic cycle which engaged the oquinone species Q 3 generated from THAP (Scheme 8). Interestingly, AuONT co-catalyst could be recovered by centrifugation and reused five times without any loss of activity.

Scheme 8 Selective aerobic oxidation of primary amines mediated by the cooperative heterogeneous system AuONT/THAP. Recently, Carbery and co-workers have been drawn to the structure of commercially available alloxan due to the structural analogy of its tautomer with TPQ cofactor (Scheme 9). The authors demonstrated that the combination of alloxan (2.5 mol%) and CuCl (1 mol%) constituted an effective homogeneous co-catalytic system for the aerobic oxidation of primary benzylic-type amines to imines under ambient air. Provided that 5 mol% of both alloxan and CuCl were used, selective oxidative cross-coupling of benzylamine with variously substituted anilines could be realized, while aliphatic amines were found to be poor coupling partners for similar reactions.

Scheme 9 Similarity between alloxan tautomer and covalently bound quinone cofactor TPQ

Although the co-catalytic system share common features with CuAOs such as the utilization of a quinone mimetic organocatalyst together with a copper salt, mechanistic investigations revealed divergence in the reaction mechanism which adopted a radical character and does not proceed through a quinone-imine step. As a consequence, the CuCl/alloxan system better resembled the flavin/alloxanmediated oxidation of amines. 30 The catalytic systems reported as yet for the oxidation of amines to imines have been designed to reproduce exquisite enzymatic reactivity and selectivity for primary amines. They function essentially under ambient air, which is the ideal oxidant in terms of safety and sustainability. In the meanwhile, the organic chemists have also sought to surpass the activity of CuAO enzymes by increasing the scope of amine substrates to sec-primary amines and secondary amines.

Bioinspired catalysts able to expand the amine substrate scope

Organocatalysts

Luo and co-workers have demonstrated that the 4-methoxy-5tert-butyl-o-quinone organocatalyst Q 4 enables efficient aerobic oxidation, at room temperature under an O 2 atmosphere, of -branched primary benzylic amines considered as poor substrates for CuAOs cofactors (Scheme 10). 31 Through DFT studies, they pointed out that the transamination pathway, plausible only for linear primary amines in nature, could also work for the oxidation of branched primary benzylic amines by Q 4 . They examined the aerobic oxidation of sec-benzylamine mediated by Q 1 and Q 4 .

In the presence of Q 1 , the reaction was stopped at the Schiff base substrate stage (Scheme 11) which was isolated and characterized by NMR analysis.

Scheme 10 Q 4 -mediated aerobic oxidation of -branched primary benzylic amines.

A strong intramolecular hydrogen bond between the imine nitrogen and the hydroxy substituent was evidenced by X-ray crystallography showing the difficulty of H-abstraction with Q 1 . In contrast, no similar hydrogen bond was observed in the Schiff base substrate stage of Q 4 , while a weak hydrogen bond was noted between C-H and the o-iminoquinone oxygen facilitating H-transfer. 31 These results may account for the different performance of p-quinone versus o-quinone in the aerobic oxidation of -branched primary amines.

Scheme 11

Intramolecular hydrogen bond characterized by Xray crystallography at the Schiff base substrate stage of Q 1 and Q 4 .

Cooperative catalytic systems

More challenging, the possibility of expanding the scope to the oxidation of secondary amines, a reaction type that CuAOs are not able to accomplish, was extensively explored. This reaction required the development of cooperative catalytic systems including a quinone-based organocatalyst.

The group of Kobayashi was the first to report a heterogeneous nanocluster catalyst acting cooperatively with Please do not adjust margins Please do not adjust margins a quinone organocatalyst cofactor for the oxidation of secondary amines to imines under mild conditions. 32 Although metal nanoclusters have been recognized as highly active catalysts for various aerobic oxidations, they had limited utility in converting amines to imines because of high temperatures required. 33 The bioinspired cooperative system consists of a heterogeneous Pt/Ir bimetallic nanocluster catalyst (0.5 mol%) immobilized on a styrene based copolymer support, and 4tert-butyl-o-quinone Q 5 (15-60 mol%) as the substrate selective organocatalyst (Scheme 12). Variously p-substituted dibenzylamines were converted, at 30°C under 1 atmosphere of O 2 , into the corresponding imines in high yields. In the case of 1,2,3,4-tetrahydroquinoline, a second dehydrogenation reaction occurred to produce quinoline. Note primary benzylic amines could also be oxidized to imines at the exclusion of amines bearing electron-withdrawing substituents.

O Q 4 (10 mol%) 1 4 2 5 OMe O H 2 N R 2 R 1 N R 2 R 1 R 2 R 1 MeCN, rt, O 2 , 48h R 1 Me, Ph 2 = Ar, thienyl 80-99% OH O O Q 1 O OMe O Q 4 O N O H Ph
Whereas the chemoselectivity of CuAOs and that of quinone-based organocatalysts Q 1 -Q 4 and IMQ for primary amines has been readily explained through the transamination process, mechanistic investigations revealed divergence in the reaction pathways because secondary amines have been shown to be inhibitors of quinones such as Q 1 through the formation of irreversible covalent adducts. 10,34 An alternative mechanism was proposed in which a quinone hemiaminal intermediate is complexed to the metal nanocluster surface and undergoes a hydride transfer process leading to the desired imine.

Scheme 12 Aerobic oxidation of secondary amines catalyzed by the Pt/Ir-Q 5 cooperative catalytic system. Doris and co-workers have reported a similar cooperative action of Rh nanoparticles, supported on carbon nanotubes (Rh-CNT) as co-catalyst with Q 5 for the aerobic dehydrogenation, at room temperature under ambient atmosphere, of N-heterocycles and dibenzylamine (Scheme 13). 35 The reaction likely proceeds through an additionelimination pathway (Scheme 14).

Scheme 13 Aerobic dehydrogenation of secondary amines catalyzed by the Rh-CNT/Q 5 cooperative catalytic system.

Scheme 14 Suggested addition-elimination pathway for the Rh-CNT/Q -mediated aerobic dehydrogenation of secondary amines.

Wendlandt and Stahl have provided the first direct evidence for the non-biomimetic addition-elimination pathway, including observation of the hemiaminal intermediate by 1 H NMR spectroscopy at low temperature (Scheme 15). They have demonstrated that the synergistic combination of 1,10-phenanthroline-5,6-dione Q 6 , with ZnI 2 as the cocatalyst, promotes, under atmospheric oxygen at room temperature, dehydrogenation of secondary amines and Nheterocycles. 36 Q 6 exhibits a bifunctional character resulting from the o-quinone moiety and the distal nitrogen atoms prone to coordination with metals. 37 The ZnI 2 co-catalyst not only enhances the amine oxidation activity, but also provides a source of iodide, which plays a critical redox role in mediating aerobic reoxidation of the reduced catalyst as shown in Scheme 15. However, the ZnI 2 /Q 6 catalytic system had some limitations as the reactions often required up to 48h to reach completion and certain product classes were not easily accessible. For example, tetrahydroquinoline underwent dehydrogenation to quinoline in only 18%. Thus, improved Q 6 -based catalytic systems were further elaborated to expand the amine substrate scope to tetrahydroquinolines, at room temperature with ambient air, as the terminal oxidant. Using an octahedral [Ru(Q 6 ) 3 ] 2+ catalyst, in combination with [Co-(salophen)] as a co-catalyst, resulted in a marked improvement of the reaction rate and led to variously substituted quinolines in high yields (Scheme 16). 38 Finally, Oh and co-workers have described a cooperative catalytic system which utilizes the synthesized 4-phenyl-onaphthoquinone Q 7 whose efficiency can be modulated through the nature of the co-catalyst (Scheme 17). 39 Using Cu(OAc) 2 as the co-catalyst, the resulting system resembles the Cu(OAc) 2 /IMQ system and allows the selective aerobic oxidation of primary benzylic amines to imines. However, in contrast to the Cu(OAc) 2 /IMQ system, it failed to oxidize nonactivated primary amines. Replacing Cu(OAc) 2 by 20 mol% TFA facilitated the formation of cross-coupled imines in high yields.

The mild aerobic oxidation protocol could be further applied to the dehydrogenation of N-heterocycles by changing Cu(OAc) 2 to Ag 2 CO 3 .

Conclusions

The development of biomimetic methods that utilize environmentally benign oxidants such as molecular oxygen or, much better, ambient air at room temperature, and avoid deleterious side reactions, is one of the most promising goals in oxidation chemistry today.

Natural CuAO enzymes have revealed their efficiency as catalysts to perform controlled aerobic oxidation of amines under mild conditions. These enzymes couple the oxidation of primary amines to aldehydes with the reduction of O 2 to H 2 O 2 , through the synergistic action of a quinone-based cofactor TPQ and a copper ion.

Recently, there has been a boost in the development of various catalytic methods for the aerobic oxidation of amines to imines given the widespread importance of imines as Please do not adjust margins Please do not adjust margins pivotal synthetic intermediates in a plethora of reactions such as reductions, additions, condensations and cycloadditions. Imines also serve as essential pharmacophores in numerous biologically active compounds.

During the last five years, researchers have begun to realize that CuAOs could constitute a rich source of inspiration for the rational design of small-molecules catalysts for the oxidation of amines to imines. Two approaches have been then envisaged.

The first approach consists of the design of biomimetic quinone-based catalytic processes, allowing to reproduce the enzymatic reactivity and selectivity for primary amines. These sytems generally function under ambient air, at room temperature and follow a transamination mechanism reminiscent of that reported for natural CuAOs. However, organocatalysts are exclusively active on benzylic amines and the discovery of more reactive quinone species able to oxidize non-activated primary aliphatic amines, which are substrates for CuAOs, remains a challenge. Through the cooperative action of a metal ion as a redox mediator, the sole Cu II /IMQ system was sufficiently reactive to oxidize non-activated primary amines because it closely resembles the enzymatic system.

In a second approach organic chemists have sought to surpass the activity of CuAO enzymes by increasing the scope of amine substrates. They have designed organocatalysts and cooperative catalytic systems for the oxidation of -branchedprimary amines and secondary amines, two reaction types that natural CuAOs are not able to accomplish. In the case of the oxidation of secondary amines, a shift from the transamination path to the addition-elimination mechanism was clearly demonstrated through the characterization of an hemiaminal intermediate. Finally, the utilization of biocompatible rather than rare and precious metals as co-catalyst should allow the development of new improved sustainable catalytic systems.

4 |

 4 Scheme 6Proposed ionic transamination mechanism for the Cu II /IMQ-mediated aerobic oxidation of primary amines to imines.

29

 29

6 |

 6 J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx

Scheme 15

 15 Scheme 15 Proposed addition-elimination mechanism for the ZnI 2 /Q 6 -mediated aerobic dehydrogenation of secondary amines and N-heterocycles; observation of the hemiaminal intermediate by NMR spectroscopy.36

Scheme 16

 16 Scheme 16 Dehydrogenation of tetrahydroquinolines to quinolines with the [Ru(Q 6 ) 3 ] 2+ /[Co(salophen)] cooperative catalytic system under ambient air.

  . Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx

  Bioinspired CuBr 2 /IMQ-mediated cascade reaction sequence leading to 1,2-disubstituted benzimidazole derivatives.

1,2-disubstituted benzimidazoles, provided slightly elevated temperatures of 45-60°C are applied (Scheme 7). 27 Scheme 7

Organic & Biomolecular Chemistry Accepted ManuscriptPublished on25 April 2017. Downloaded by Universite Paris Descartes on 26/04/2017 14:21:22. View Article Online DOI: 10.1039/C7OB00507E

This journal is © The Royal Society of Chemistry 20xx J. Name ., 2013, 00, 1 -3 | 7

Organic & Biomolecular Chemistry Organic & Biomolecular Chemistry Accepted Manuscript Published on 25 April 2017. Downloaded by Universite Paris Descartes on 26/04/2017 14:21:22. View Article Online DOI: 10.1039/C7OB00507E

Acknowledgements

The author would like to thank CNRS and Paris Descartes University for financial support. Co-workers and students listed in references 13, 20, 22-24 and 27 are gratefully acknowledged for their research contributions.


Victor Rosi

Olivier Houix

Nicolas Misdariis

Patrick Susini

Uncovering the meaning of four semantic

published or not. The documents may come   L'archive ouverte pluridisciplinaire

Uncovering the meaning of four semantic attributes of sound : Bright, Warm, Round and Rough victor.rosi@ircam.fr Victor Rosi 1 , Olivier Houix 1 , Nicolas Misdariis 1 , Patrick Susini 1

Interviews with sound experts [START_REF] Carron | Speaking about sounds: a tool for communication on sound sound features[END_REF] Sound perception and sound design group, STMS Lab (IRCAM-CNRS-SU), Paris, France

The present study aims to understand the use and the definition of four terms selected from the sound lexicon developed by Carron et al. [START_REF] Porcello | Speaking of sound: language and the professionalization of sound-recording engineers[END_REF] . Bright (brillant), round (rond), warm (chaud) and rough (rugueux) are four terms vastly used in the French language for sound description in sound creation processes such as music performance, orchestration, sound engineering or sound design. Yet, they lack formal, standardized definitions. The goal is to get definitions, or semantic portraits, for each word with corresponding sound samples from a musical instrument dataset. Metaphoric -extracted from literature [START_REF] Carron | Speaking about sounds: a tool for communication on sound sound features[END_REF] [3] [4] [START_REF] Wallmark | A corpus analysis of timbre semantics in orchestration treatises[END_REF] Crossmodal correspondance (CMC) warm (chaud), harsh (dur), clear (clair) Matter (shape, density, material) round (rond), full (plein), organic (organique) Effect enveloping (enveloppant), scratching (qui gratte) Affect pleasant (agréable), aggressive (agressif), straightforward (franc)

Semantic Analysis Methods

Acoustic

Definitions & Sound samples

Context

• A bright sound has most of the spectral energy in the high frequencies. It is often a high-pitched sound that can be composed with a sharp attack.

• A warm sound tends to be a low-pitched or mid-low-pitched sound. It gives a feeling of spectral richness in the mid-low frequencies. It has a rather soft attack and it is a fairly pleasant sound that gives a sensation of envelopment.

• A round sound has a soft attack and is temporally stable. It tends to also have a soft release or a long resonance. A round sound is spectrally perceived as full with a spectral balance located in the mid-low frequencies.

• A rough sound is temporally unstable ; it presents fast temporal variations that can bring some sort of noise. It gives a rubbing/scratching sensation. • Lemmatization [START_REF] Sagot | The Lefff, a freely available and large-coverage morphological and syntactic lexicon for French[END_REF] Lemma/Interviewee frequency for each term Perspectives

Glockenspiel hard stick

•

  Participants : 32 French-fluent sound experts (musicians, composers, sound engineers, sound designers, acousticians …) • Sound dataset : Studio online Library & Vienna Symphonic Library (~600 musical instruments sound samples) • Duration : ~2h10 • Structure : Divided in four parts (for each term) • Questionnaire : Q1 : Frequency and context of use of the studied term Q2 : Definition of the studied term Q3 : Sound samples for the studied term Q4 : Sound samples for the opposite of the studied term Q5 : Definition of the opposite of the studied term Q6 : Investigation of the affect aspect of the studied term

  Trumpet brassy Bass clarinet ordinario Cello ordinario Doublebass pizzicato Marimba soft stick Tuba ordinario Winds flatterzunge Bassoon multiphonics Strings sul ponticello • 10 categories of sound description with verbal examples translated in English along with the original verbatims in French. • Categories were validated with the top 50 lemmas by 4 experts -Fleiss' kappa : 𝜅 = 0.69 (p< 0.001) Online survey (in progress) Goal : Reduce/Hierarchize the quantity of relevant information in order to build more robust definitions Corpus : Phrases extracted from Q2 and Q5 for each term, based on the most occuring lemmas Populations : French-fluent sound experts Questions (example) : -According to you, the meaning of the concept "high-pitched sound" is : accurate/ vague / incomprehensible -In your opinion, is a bright sound a high-pitched sound ? Strongly agree … Strongly disagree / Non relevant • Tokenization


Victor Rosi
email: victor.rosi@ircam.fr

Olivier Houix

Nicolas Misdariis

Patrick Susini

UNCOVERING THE MEANING OF FOUR SEMANTIC ATTRIBUTES OF SOUND : BRIGHT, ROUGH, ROUND AND WARM

Bright (brillant), round (rond), warm (chaud) and rough (rugueux) are four terms vastly used in the French language for sound description in sound creation processes such as music performance, orchestration, sound engineering or sound design, yet they lack formal, standardised definitions. Therefore, the intent of the present study is to obtain definitions and matching sound samples of these four terms as they are interpreted by different sound professionals. This work was organized around individual interviews with 32 sound professionals (musicians, composers, sound designers, acousticians. . . ), during which they were asked to give definitions of the four terms and to discuss their opposite concepts. The analysis of the interview verbatims through qualitative analysis and standard NLP (Natural Language Processing) methods allows us to unravel the various sound description strategies. Based on literature review on timbre semantics we reveal relevant categories for the clustering of the descriptions across the four terms. These categories mainly group acoustic, source-related and metaphorical descriptions produced by the sound professionals. The experts were also asked to choose sound samples from a musical instrument database to complete the definition of each word. By analyzing the descriptions and comparing them to the selected sound samples, we formulate definitions of the four terms along with a few hypotheses on the acoustic correlates involved, thus assessing the potential plurality of perception among the experts.

INTRODUCTION

As suggested by Lemaitre et al. [START_REF] Lemaitre | Listener expertise and sound identification influence the categorization of environmental sounds[END_REF], environmental sound identification is mostly related to listeners' expertise in the field of sound, and to their capacity to identify the sounds. In other words, experts use acoustic characteristics more than non-experts, and more so for sounds that are not easily identifiable. Apart from pitch, duration, and intensity, sounds can be described via their timbral aspects. Warm, sharp, smooth, round, bright, rough, nasal are all frequently used in many languages. It is often considered in western cultures that the trumpet produces arguably one of the brightest sounds among the instruments of an orchestra, and that a bright sound has a high spectral centroid. While this affirmation about brightness seems to be generally assumed by the entire community of sound professionals when describing different kind of sounds [START_REF] Peeters | The timbre toolbox: Extracting audio descriptors from musical signals[END_REF] [START_REF] Misdariis | Environmental sound perception: Metadescription and modeling based on independent primary studies[END_REF], there are timbre-related terms that do not have an obvious semantic nor acoustic definition which would enable clear intersubjective comprehension and usage. Revealing the meaning of timbre-related terms would facilitate communication in numerous fields [START_REF] Carron | Speaking about sounds: a tool for communication on sound features[END_REF]. It is therefore crucial to assess the richness of perception of this vocabulary from a population of users.

Several studies discuss the semantic of words used by sound professionals or musicians to describe timbre in particular situations. Disley [START_REF] Disley | Spectral correlates of timbral semantics relating to the pipe organ[END_REF], gave account of seven terms often shared among a panel of musicians for the description of the pipe organ's timbre clear, thin, warm, bright, flutey, full and balanced. In a study on piano, Bernays and Traube [START_REF] Bernays | Verbal expression of piano timbre: multidimensional semantic space of adjectival descriptors[END_REF] elaborate the most relevant terms for sound description that seem to rely on two dimensions: percussion and resonance. Finally, their results included five words, bright, dry, dark, round and velvety. With different methods, many other studies show similar results related to how experts speak about timbre for specific sound sources such as the classical guitar [START_REF] Traube | An interdisciplinary study of the timbre of the classical guitar[END_REF], the violin [START_REF] Saitis | Perceptual evaluation of violins: A quantitative analysis of preference judgments by experienced players[END_REF], or the piano [START_REF] Cheminée | Analyses des verbalisations libres sur le son du piano versus analyses acoustiques[END_REF]. Several papers argue that semantic description of timbre seem to be associated to specific perceptual dimensions of timbre. Von Bismarck [START_REF] Bismarck | Timbre of steady sounds: A factorial investigation of its verbal attributes[END_REF], in his study on timbre semantics, identified four great structures of timbre as dull-sharp, full-empty, colorful-colorless and compactdiffused. In the 1960s, in his Traité des objets sonores, Schaeffer [START_REF] Schaeffer | Traité des objets sonores[END_REF] proposed similar dimensions that describes only sound features called mass, harmonic timbre and grain. More recently, Zacharakis [START_REF] Zacharakis | An interlanguage study of musical timbre semantic dimensions and their acoustic correlates[END_REF], as a result of a VAME1 procedure determined three principal dimensions providing a good general structure for timbre, luminance, texture and mass. In spite of the fact that many of the perceptual dimensions identified across the studies are similar, these dimensions don't clearly include a metaphorical description employed by experts. In an anthropological research on sound professions, Porcello [START_REF] Porcello | Speaking of sound: language and the professionalization of sound-recording engineers[END_REF] noted five strategies for timbre description used by producers and sound engineers with some being metaphorical, related to affect or imitations. Faure [START_REF] Faure | Des sons aux mots, comment parle-t-on du timbre musical?[END_REF], in her thesis work assessed the semantic categories in a population of musicians and naive listeners and found nine semantic categories, some related to sound's physical aspects and others more metaphorical. In his thesis, Carron [START_REF] Carron | Définir une identité sonore de marque: méthodologie et outils[END_REF], parsed the literature on timbre semantics and identified three kinds of descriptions : The causal description, related to the source and the excitation mode, the contextual description corresponding to metaphorical and emotional aspects of sounds and the reduced description that deals with sound physical properties. In a semantic analysis of an orchestra treatises corpus, Wallmarck [START_REF] Wallmark | A corpus analysis of timbre semantics in orchestration treatises[END_REF] identified seven semantic categories used by the authors while describing the instruments' timbre. The semantic categorisations of the description of timbre of the presented research show similar results such as the affect-emotion-judgement category, the crossmodal correspondance (CMC) category, the imitation category, and the "reduced listening" category.

The present study aims to understand the use and the definition of four terms selected from the sound lexicon developed by Carron [START_REF] Carron | Speaking about sounds: a tool for communication on sound features[END_REF] as they are cited in numerous studies for sound description. Brightness (brillance) is defined in several surveys, and seems to be well understood semantically and acoustically. It would therefore make a great point of reference for our study. Besides, some works point out that brightness doesn't only rely on high spectral energy but also on other spectral details, and that it also has a certain correlation with sharpness ( [START_REF] Ilkowska | Sharpness versus brightness: A comparison of magnitude estimates[END_REF]). Warm (chaud) and round (rond) are two concepts often used in the French language for timbre description that have several similarities of use as observed by [START_REF] Carron | Définir une identité sonore de marque: méthodologie et outils[END_REF] and [START_REF] Traube | An interdisciplinary study of the timbre of the classical guitar[END_REF]. They are difficult to interpret because there is no clear opposite term to warm nor round, thus there is no apparently clear dimension for those terms. Roughness (rugosité) is defined psychoacoustically as the proximity of frequencies in critical bands of the inner ear [START_REF] Terhardt | On the perception of periodic sound fluctuations (roughness)[END_REF] producing the sensation of a modulation of sound. In addition, the concept of graininess (granulosité) in French language is used for sound description, and seems to interfere with the definition of Roughness. This work will be based on interviews with sound professionals from different fields. Bright, warm, round and rough are the four terms studied during the interviews. The goal is to give definitions, or semantic portraits, for each term, illustrated with sound samples from a musical instrument database that enable speculation about the acoustic features involved in the perception of each word.

METHODS

Expert Panel

32 French-fluent sound experts participated in the interviews, 23 males and 9 females with an average age of 38 years ranging from 27 years to 69 years. Among the 32 participants, 3 are not French natives but have been working in France for more than 10 years. The choice of the panel was led by the idea of acquiring a potential diversity of perception based on the diversity of professional experiences, and by the idea that experts have a more coherent speech about sound than non-expert listeners. Hence, they are led to communicate about sound as part of their professional practice. We tried to obtain close to equal proportions of composer, sound engineer, musicians and sound designers. Many of these experts have multiple hybrid profiles, for example two of the experts are both sound engineers and sound designers.

Sound dataset & Apparatus

Choosing a sound dataset for the interview was crucial as the extracted sound samples should represent the perception of the studied terms. An environmental sound library would be a good type of sound dataset, although this kind of sound promotes everyday listening ( [START_REF] Gaver | What in the world do we hear?: An ecological approach to auditory event perception[END_REF]) which produces a sound description strongly related to the nature of the sound source. A dataset of synthetic sounds could not be an option either, since the purpose of the subsequent study is to obtain the acoustic features involved in our perception of the four terms. Therefore we chose to use a dataset composed of 26 musical instrument sounds with different playing techniques. We arbitrarily discarded playing techniques that seemed redundant with the standard playing style (called ordinario for this dataset), or that were not relevant with regards to timbre description. The purpose of the selection was to have a proportion of sounds easy to manage for both the interviewer and the interviewee through a shared interface. Therefore, we used the sound library recorded at IRCAM from the project Studio-Online Library (SOL) [START_REF] Ballet | Studio online 3.0: An internet" killer application" for remote access to ircam sounds and processing tools[END_REF] mixed with parts of the Vienna Symphonic Library (VSL2 ) for some instruments that we judged to be valuable but missing in the SOL. To enlarge the dataset composed of strings, woodwinds and brass, we added tonal keyboards as percussive instruments. The rule was to always have a distinctive pitch for each sound sample (except for the multiphonic playing technique). The complete dataset of instruments is reported in Tab. 1. Each instrument has a set of playing technique options, at different pitches and different intensities, in the ranges specific to each instrument. So there were standard playing techniques, with others more contemporary, depending on the instruments, like multiphonics and flatterzunge for the wind instruments, or Bartók pizzicato for the string instruments. We selected only octaves of C 3 in order to reduce the amount of sound samples. We motivate the diversity of pitch both with the fact that instrument timbre varies with register, and that pitch information for timbre-related terms was mentioned in Carron's interview. [START_REF] Carron | Speaking about sounds: a tool for communication on sound features[END_REF] with sound experts. For comfort reasons, we equalized the loudness of each sound sample following the EBU norm on loudness (R-128), setting all the sounds to -23 LUFS. One of the participants felt strained by this normalization as they felt the sounds were subsequently de-naturalized. The 32 interviews lasted approximately two hours and took place in quiet environments such as in a studio at IRCAM, at the expert's home, or at the expert's workplace. The setup was composed of an interface coded in Max/MSP giving easy access for listening to the sounds as they were sorted by instrument families, instruments and playing techniques. Interviewer and interviewee listened to the sounds through open headphones Sennheiser HD 650 allowing to listen to sound samples and to discuss them without having to take on and off the headphones, making the interview more comfortable. Every interview was recorded via the Max/MSP interface by using a SHURE MV5 microphone.

Interview procedure

Global process

The four terms were discussed sequentially with each of the participants. The order of presentation of the terms followed a Klein Four group permutation. Hence, one interview presented the term in the order of the first line, while the next expert interview would follow a permutation. This interview was designed as a semi structured qualitative interview, while some questions expect a specific type of answers (sound samples), other questions expect free verbalisations.

Questionnaire

There are six main questions composing the body of the interview:

• Q1 : What is the context and frequency of use of the studied term ?

• Q2 : Can you give a definition of the studied term ?

• Q3 : Considering your definition, can you try to find at least three sound samples that correspond to the studied term ?

• Q4 : Can you try to find at least three sound samples that correspond to the opposite of the studied term ?

• Q5 : Can you define the opposite of the studied term ?

• Q6 : Is there any affect related to the perception of this term and its opposite ?

The interview would start after a presentation of the questionnaire along with quick overview of the sound dataset. The purpose of Q1 was to give a contextual framework to the expert so that they can more easily relate to each term. It also gives valuable quantitative information about the frequency of use of the term. In Q2, the interviewee was invited to define the term. We try to obtain information on more acoustical aspects and we avoid mentioning any affect-related description of sound, as it is treated in Q6. For Q2 and Q5, the researcher would participate by facilitating the expression of the interviewee with follow-up questions and probes. Q3 was the opportunity for the expert to find sounds related to the terms in the database. If needed, the researcher helped the expert to spot related sounds, based on elements from the definition previously established. The interviewee had to select at least three different sounds if possible. In the second part of the questionnaire, we investigated the opposite concept of the studied Term. The purpose is to refine the answers from Q2 and Q3 and to evaluate a potential semantic polarity between two terms. Q4 has the same process as Q3, only this time we selected sounds for the opposite term naming it yet. Q5 is focused on the definition of the opposite concept of the term. Finally Q6 interrogates the presence of affect elements in the definition of the term and the opposite concept. At the end of Q3 and Q4, the interviewer asked the interviewee if there were a sound missing for the sound description of the term. Q1, Q4, Q5 and Q6 will be addressed in a subsequent work, as we only focused our analysis on Q2 and Q3 for this paper.

Analysis

As evoked by Saitis [START_REF] Saitis | Perceptual evaluation of violins: A quantitative analysis of preference judgments by experienced players[END_REF] in their study on perception of violin timbre, there are two opposed points of view regarding qualitative analysis. Some believe that the researcher should analyse all data without any assumptions, while others think the researcher should enter the field with their hypotheses in mind [START_REF] Strauss | Grounded theory in practice[END_REF]. We followed a hypotheticodeductive method and considered prior knowledge and assumptions of semantic timbre literature to create categories of description strategies structuring the following analysis of the interview transcripts. Some categories emerged after analysis of the verbatims. For example, one of these categories is related to the dataset of musical instrument sounds and their features. After transcribing the interviews, we extracted the definitions of the investigated terms. To this purpose, we focused on the analysis of Q2. Answers got through basic steps of natural language processing (NLP) : First we tokenized (i.e. slicing sentences into words) the transcripts of the text with the nltk toolbox. Secondly we discarded the stop words. Thirdly we lemmatized the tokenized text, based on an adapted version of Sagot's lexicon [START_REF] Sagot | The lefff, a freely available and largecoverage morphological and syntactic lexicon for french[END_REF], lemmatization is the process of putting a word into its canonical form so it can be grouped with other words.

Finally, We were able to assess the lemma/interviewee frequency (i.e. the number of interviewees using one lemma for each definition).

Manual filtering

In order to only keep relevant units of verbal description in their investigation of timbral attribute queries for sound effect libraries, Pearce et al. [START_REF] Pearce | Timbral attributes for sound effect library searching[END_REF] followed several steps of manual filtering. We propose a similar process that was run and reviewed by the four authors. Each ambiguous verbal unit was thus inspected in terms of its context. One lemma was removed if its meaning was inconsistent more than 50% of the time. For instance, there was confusion about whether the term "aspect" was to be used to describe the aspect of the sound, or the fact that the sound had multiple aspects. "Aspect" was thus removed. If a lemma possesses multiple meanings and one of them is substantially present in the corpus, we would keep it and only discard the number of occurrences of the word in irrelevant contexts. One example is the term "variation" which, in most cases, metaphorically defines the sound's temporal shape but is sometimes employed as a syntactic tool. Finally, if lemmas shared the same concept and the same root, they were grouped together under the most frequent lemma of the two. For instance, "bright" and "brightness" were grouped together under the lemma "bright". Moreover, in order to drastically reduce the corpus, we did not consider the hapaxes 4 for analysis.

Interpretation of the results

The information presented in the the lists of lemmas corresponds to the vocabulary used for the definition of the four terms. We were able to give semantic portraits of the four terms, through a manual excavation of the syntactic context of those words. There were metaphorical adjectives like "high", "big", "sharp" or "generous" and sometimes dimensions of sounds such has "frequency", "harmonics" or "attack". A substantial part of the definitions given by the experts were phrased negatively (e.g. "not loud", "not sharp"...). In those cases, it was crucial to check the context of each lemma. For example if the term "high" (pitch or frequency) is cited by a great amount of experts for bright, round and warm, it doesn't mean that they all have high fundamental frequencies or high spectral centroid. Sometimes some words were used with quantifiers like "a little", "few", "not too much" etc. We did not employ these because of their diversity and the fact that we do not have a fully automatic approach towards text mining.

The sound samples collected in Q3 had four features: Instrument, playing technique, pitch and intensity. For the results, we focused on the instrument and the playing technique. If an instrument/playing-technique combination were to be selected by more than a third of the 4 verbal units that appears only in one source (one interviewee) in the raw data population of experts, then it was considered as a good example for the studied term. Pitch and intensity were also considered if they were obviously related to some of the relevant verbal descriptions.

RESULTS

Here are the 50 most frequently used terms for defining the four words (Q2) after manual filtering in Tab. 2 The top 50 words used for the definition are ranked according to the word/interviewee frequency. For instance, 100% of the experts employed the term "warm", which is not surprising as it is one of the four investigated words. We can find acoustic information in the 50 most-used terms on spectral, temporal or loudness aspects. It is worth noting that there are many ways to indicate spectral or pitch information in French. For instance aigu, and haut, will both describe high pitch or high frequencies. The same is true for grave, bas. Basse is more ambiguous as it can describe the bass clarinet or low frequencies. The fact that experts mentioned instruments like clarinette or percussion is vastly influenced by the sound dataset, which is only composed of musical instruments. Many words imply a metaphorical description such as pur, plein, and agressif, among others.

Description strategies

Informed by the literature on semantic analysis of timbre [START_REF] Porcello | Speaking of sound: language and the professionalization of sound-recording engineers[END_REF][START_REF] Faure | Des sons aux mots, comment parle-t-on du timbre musical?[END_REF][START_REF] Carron | Définir une identité sonore de marque: méthodologie et outils[END_REF][START_REF] Wallmark | A corpus analysis of timbre semantics in orchestration treatises[END_REF], and our assumptions, we proposed 10 description strategies in order to analyse the definitions. Coding and re-coding a corpus is a common step present in many qualitative studies like Weston's study [START_REF] Weston | Analyzing interview data: The development and evolution of a coding system[END_REF] or in Saitis's study [START_REF] Saitis | Perceptual evaluation of violins: A quantitative analysis of preference judgments by experienced players[END_REF] in the field of semantic timbre. In order to test the validity of the description strategies, an inter-rater analysis was performed. The four authors sorted the 50 top lemmas present in Tab. 2 into the 10 categories. Then, we computed Fleiss' kappa, an index that evaluates the inter-rater agreement in the sorting task. Since a big part of the timbre language is metaphorical and can be interpreted through different modalities, there was some disagreement but we suggested to always consider the context of the word and the definition from Trésor de la langue franc ¸aise database5 to make a decision. Nonetheless, Kappa got a score of κ = .69, which reflects a substantial agreement according to Landis and Koch's interpretation on Kappa values. We then refined the categories and their definitions by collectively sorting the top 50 words one more time.

The 10 categories of description strategy were grouped in three greater classes:

The first class gathers all acoustic aspects of sounds like the discourse related to reduced listening proposed by Carron [START_REF] Carron | Speaking about sounds: a tool for communication on sound features[END_REF]. There are temporal and spectral descriptions, but also dynamic and intensity aspects of sound, along with all of the lexical fields that are explicitly related to the sound domain such as "resonant", "noisy", or "nasal".

The second class groups all of the metaphorical aspects of sound. Hence, there is the crossmodal correspondance (CMC) category that you can find in other works [START_REF] Faure | Des sons aux mots, comment parle-t-on du timbre musical?[END_REF][START_REF] Carron | Définir une identité sonore de marque: méthodologie et outils[END_REF][START_REF] Wallmark | A corpus analysis of timbre semantics in orchestration treatises[END_REF] that contains lexical fields related to other senses, such as sight, touch and taste. For example, "soft", "harsh", "clear"... A second metaphorical sub-category group of lemmas related to matter's characteristics is another category present in Wallmark's work [START_REF] Wallmark | A corpus analysis of timbre semantics in orchestration treatises[END_REF] that discusses the material, shape and density of sound as matter or as an object. For example, "round", "full", "organic"... The third category is the one related to affect, emotional value and judgement vocabulary employed for sound description, present in all the studies cited above. Although Q6 was supposed to concentrate all descriptions on affect, experts would still use this dimension to give the definitions in Q2. For example, "aggressive", "warm"* (see Tab. 2), "rich", "pleasant"... The last metaphorical category groups all the vocabulary that evokes sound's action having an effect on the listener, the surroundings, or its behaviour. For example, "enveloping", "scratching". The third class collects the references to the sound source. It corresponds to the causal listening evoked by Carron [START_REF] Carron | Speaking about sounds: a tool for communication on sound features[END_REF] and Gaver [START_REF] Gaver | What in the world do we hear?: An ecological approach to auditory event perception[END_REF]. There were information on the source mainly represented by naming the instruments present in the dataset. For example, "clarinet", "percussion", "voice". There were also characterisations of the excitation mode or the playing technique. For example, "bow", "rub", "impact" ...

Definitions and sound samples

Figure 1 presents how the experts spoke about the terms. We observe that the acoustic aspects of Bright, were al-

Acoustic

Sound vocabulary, Dynamic, Spectrum, Temporality Source Source, Excitation mode/Playing technique Metaphore CMC, Matter (Material, shape, density), Effect, Affect In order to orient the definitions toward acoustic features of sound, we started by describing the acoustic semantic categories first and then joined the related metaphorical description (e.g. "a soft attack" -"harmonic richness"...). Then, considering its relevance, we proceeded to purely metaphoric descriptions, references to the source or the excitation mode. All percentage values in the definitions correspond to the proportion of experts among the total number of experts that evoked a semantic category or concept. We also reported the relevant sound samples for each term, in order to relate them to the descriptions from Q2. At the end of the description, we tried to summarize the relevant information for each term.

Bright

When defining brightness, a large part of the expert population (97%) gave spectral information. 90% of the population indicated that a bright sound has substantial spectral content located in the high frequencies. More generally, it means that a bright sound gives a sensation of richness in high frequencies. There was sometimes confusion between whether the fundamental frequency or the spectral content was high. Some experts would say that a low pitched sound is difficult to identify as bright (38%). Even though the temporal aspects don't seem to be very important to the majority of the population (see Fig. 1, 25% of the experts considered that the presence of a rather "sharp/fast" attack adds a feeling of brightness. That can be related to an excitation mode cited by 22% of the experts such as "articulated", "impact sound", or "tongued". For the mentioned sound sources, 31% of the experts referred to metallic sources (glockenspiel, brass instruments, metal, concert flute...). On a metaphorical level, 69% of the experts defined sound through the CMC category mostly in the lexical field of light. Examples: "clear", "halo", "shine", "luminous".

As for the sound samples, coherently to the verbal description, most of the sounds chosen were played by high pitched instruments (trumpet, glockenspiel, piccolo, violin) on high register. If an instrument played louder, more harmonics are perceived, which seemed to influence the selection of sounds. 90% of the experts estimated that the sound of the glockenspiel played with hard sticks was a bright sound. The fact that they explicitly chose glockenspiel sound with the hard stick corroborates the fact that brightness is related to the attack of sound. The second kind of sound most selected was the trumpet (75%) played ordinario 6 mostly in the high register (C5-C6) and in loud dynamics (forte-fortissimo).

To summarize: A bright sound has most of the spectral energy in the high frequencies. It is often a high-pitched sound. It can be composed with a sharp attack.

Warm

When investigating the term warm, we first notice the fact that it is semantically comparable to round. The two terms were compared either in the definition of warm or in the definition of round by the entire panel of experts. Some of the experts would even accidentally use one in the place of the other during the interviews. As for bright, a large part of the experts (94%) described warm through spectral aspects. 34% of the population evaluated a warm sound as "low-pitched". Since rich timbre is correlated with spectral variation by some studies in the English language ( [25]), we chose to compare the term "rich" to spectral information. The harmonic content was therefore sometimes described as "rich" (28%), with spectral energy mainly located in the "low" and "medium" frequencies and less information in the high frequencies (87%). When referring to the temporal aspects (66%), the experts mostly qualified the attack as being "not sharp", or "soft". Considering the sound sources, they would give examples in the low string instruments like the cello or the double bass and some of them would evoke a "breathed" component in the sound (22%). As for the excitation mode, the idea of a "vibrated" sound is sometimes evoked as enhancing a warm aspect in sounds (22%). Warm is strongly related to affect and behavioral dimensions (by more than 80% of the population) in a very metaphorical way. Hence it is described as enveloping (30%), lively (13%) and compared to a human behavior or the human voice (13%). A warm sound is also positively described by 34% of the experts as "comfortable", "pleasant", "reassuring", "generous", "giving happiness"... 6

ordinario: standard playing technique

The most cited warm sound is the bass clarinet (69%), played ordinario, medium or low pitched (C2-C3), in small dynamics (pianissimo-mezzoforte). These sounds appear to have most of the spectral content close to the fundamental harmonic, with a breathing noise on the notes played pianissimo. 56% of the experts indicated that for the cello played on a C3 or C4 ordinario (i.e. with a vibrato for the strings) mezzoforte or piano was a warm sound. It is low to medium pitched with a certain timbral or harmonic richness, the vibrato enhancing the perceived expressive aspects in the sound. We could imagine that both the breathy sound of the bass clarinet and the vibrato of the cello might add a feeling of richness that amplifies the warm quality of a sound. Finally, the sound of a French horn played ordinario between C2 and C5 in a mezzoforte or pianissimo dynamic was elected as warm by 34% of the experts.

To summarize: A warm sound seems to be a lowpitched or mid-low-pitched sound. It gives a feeling of spectral richness in the mid-low frequencies. It has a rather soft attack and it is a fairly pleasant sound for the listener, giving a sensation of envelopment.

Round

Round, as previously stated, was always compared to warm. 91% of experts gave a spectral description of round. While most of the experts said that the spectral content of a round sound is located in the mid-low frequencies, others said that it could also have energy in the high frequencies. The idea of richness is evoked by fewer experts than for warm (16%) and it is both used positively and negatively. Nonetheless 38% of the experts preferred the idea of a round sound in the mid-low frequencies with little spectral energy in the high frequencies, 16% using the term "balanced" to this end. 32% of experts described a round sound or its spectrum as "full", which can be correlated to the fundamental frequency or the number of overtones ( [START_REF] Zacharakis | An interlanguage study of musical timbre semantic dimensions and their acoustic correlates[END_REF]). Round was also described through temporal aspects by 84% of the panel. More specifically, 70% of the experts focused on the nature of the attack, or the transient. Some experts would say that a round sound has no or little attack, some others would describe it metaphorically (CMC, Affect) like "soft, "not sharp", "not harsh" or "not aggressive". It was physically described as "slow" or "long". Some experts described the release of a round sound as being "long" or "soft" explaining that a round sound are quite resonant. Another temporal aspect cited by some experts (28%) was temporal stability. Experts would describe a round sound as stable, with an absence of "parasitic noise". It can be related to metaphorical description of a round sound such as "perfect", "soft", "pure" or "homogeneous" (25%). Hence a round sound seems to carry little noise or variations over time. Dynamic was discussed by 50% of experts, and 19% of experts identified a round sound as not being very loud. As for warm, there were many positive descriptions in the domain of affect, but to a lesser extent than warm. 34% of the experts thought a round sound to be "pleasant", "reassuring", "expressive", "ideal", "generous" and "not aggressive".

The first sound to be selected by 60% of the experts was a pizzicato of doublebass, played C2 or C3 with an intensity ranging from pianissimo to mezzoforte. It is a low pitched and resonant sound with a majority of spectral energy around the fundamental frequency, and a soft attack. It doesn't have any special harmonic or dynamic variation. Even though it is one of the shortest sounds of the dataset, it matches the temporal and spectral definition. The marimba played pianissimo with soft sticks in a pitch interval from C2 to C5 was mentioned by 56% of the population as a round sound. It has similar spectral and temporal properties as the pizzicato of the double bass. 53% of the experts found the sound of the high register (C3-C4) of a bass tuba played piano to be round. It is also a long and stable sound, with a soft attack. The French horn, playing in the same register and in the same dynamic, is cited by 34% of the population. Here we have two kinds of sounds, one is damped, resonant and low pitched, the other is sustained and stable. They all have a soft attack that could be related to the attack time and a spectral energy located in the mid-low frequencies.

To summarize: A round sound has a soft attack, and is temporally stable. It tends to also have a soft release or a long resonance. A round sound is spectrally perceived as full with a spectral balance located in the mid-low frequencies.

Rough

From Figure 1, rough didn't have as clear a path of expression on the acoustic dimensions as the other terms. Nonetheless, it is possible to relate temporal aspects (62%) to elements from metaphorical categories such as Excitation mode (56%), CMC (72%) and Matter (62%). Starting with the temporal and timbral aspects, a rough sound was defined as "unstable", "irregular", "with variations", "noisy" (34%), "with parasitic noise" (38%), or with a sensation of a pulse (28%). It can be linked to more metaphorical descriptions: via the Action/Behavior category, "scratching", "shredding", or "random" (34%), via the CMC category, "asperities", "texture", "resistance" or "graininess" (32%) and via the Matter or affect category, "not pure", "not homogeneous", "raw", or "not clean" (32%). Graininess was a concept mentioned by some experts (16%) as a different kind of roughness. However, the difference of perception between those terms remains unclear. Roughness was also expressed through the excitation mode of the source, like "rubbing" or "friction" (41%).

Unlike the three other terms, it seemed that the discriminant feature for rough sound sample selection wasn't the instrument but rather the playing technique. As it is not really related to the spectrum nor the pitch, several instruments with the same playing technique would produce a comparable sensation of roughness. Hence, 81% of the population evaluated a wind instrument playing a flatterzunge to be rough. The trumpet playing a flatterzunge, selected by 32% of the experts, might present a rougher flatterzunge than other instruments. The contrabassoon is interesting as its lowest note produced a similar effect of rapid pulses as the flatterzunge. It was mentioned by 41% of the experts as either being played ordinario, or flatterzunge. The second most frequently occurring type of rough sound was the multiphonics produced by the woodwinds (66%). The instrument producing the most rough multiphonics according to the panel were mainly the bassoon (56%) and the clarinet (25%). As there is a variety of multiphonics, it is notable that those mentioned presented the same pulsing effect as the flatterzunge paired with an inharmonicity, due to the multiple notes played at the same time. Finally, 41% of the experts chose string instruments playing sul ponticello, echoing the "rubbing" excitation mode that was cited above. When playing sul ponticello a string instrument player rubs the string with the bow very close to the bridge, thus producing a friction sensation of instability of the harmonics and a noisy sound. It is unclear how the psychoacoustical definition of roughness relates to the sul ponticello sound, while it seems to match the sounds of flatterzunge and multiphonics.

To summarize: A rough sound is temporally unstable, it presents fast temporal variations that can bring some sort of noise. It gives a rubbing/scratching sensation.

GENERAL DISCUSSION

The goal of this study was to obtain definition and related sound samples for four terms frequently used for timbre description through the process of several expert interviews. The definitions of the terms were close to those obtained by Carron [START_REF] Carron | Définir une identité sonore de marque: méthodologie et outils[END_REF] in his sound lexicon. With the definitions, we get new clues on the acoustic features involved in the definition of the terms. They also display the variety of description strategies employed by sound experts in the French language. As we wanted to follow a methodology with few assumptions, we started with free verbalization (Q2, Q5). It allowed us to have new insights on the underlying acoustic features. In future work, Q5 will be investigated in order to reinforce the definition obtained in Q2, through an online survey presenting both verbalisations from Q2 and Q5. While bright got a clear definition, warm and round seem to share similarities in their definitions, but they were better differentiated with the selection of sound samples, an observation that begs for further investigations. The same goes for rough that was mainly defined through CMC aspects but with very eloquent corresponding sound samples. This point suggests that verbal descriptions might not be a good way of defining certain sound attributes, and that giving a definition through sound samples is a better approach.

Finally the next step of this study will be to reveal the underlying acoustic features of these definitions.

Figure 1 :

 1 Figure 1: Proportion of experts that expressed information in each of the 10 categories for the four terms. Normal : Acoustic ; single stripe : Source ; double stripe : Metaphoric

Table 1 :

 1 Instruments from the SOL and VSL which compose the dataset. In italic : sound samples from the VSL

	Strings	Woodwinds	Brass	Percussions	Other
	Violin	Concert flute	Trumpet	Glockenspiel Guitar
	Viola	Piccolo flute	Trombone	Xylophone	Harp
	Cello	Alto flute	French horn Vibraphone	Accordion
	Double bass Oboe	Bass tuba	Marimba	Piano
		English horn
		Bb Clarinet
		Bass clarinet
		Alto Saxophone
		Bassoon
		Contrabassoon

Table 2 :

 2 Top 50 relevant words used for defining the four words.

	Term	Rank W/I (%) Term	Rank W/I (%)
	warm* chaud	1	100	blow souffle	15	34
	bright brillant	2	97	rub frotter	16	31
	round rond	2	97	warm* chaleureux	16	31
	high aigu	3	88	aggressive agressif	17	28
	harmonic harmonique	4	84	voice voix	17	28
	rough rugueux	5	81	harsh dur	18	28
	attack attaque	5	81	music musique	18	28
	low** grave	6	69	percussion percussion	19	25
	spectrum spectre	7	66	resonant résonant	19	25
	medium médium	8	56	clarinet clarinette	19	25
	timbre timbre	9	53	musical musical	19	25
	frequency fréquence	9	53	hertz hertz	19	25
	string corde	9	53	pur pur	19	25
	loud fort	9	53	dynamic dynamique	19	25
	soft doux	10	50	bow archet	20	22
	full plein	11	47	homogeneous homogène	20	22
	rich riche	12	41	nuance nuance	20	22
	low** bas	12	41	sustained entretenu	20	22
	matter matière	13	38	color couleur	20	22
	noise bruit	13	38	balanced équilibré	20	22
	low** basse	13	38	temporal temporel	20	22
	smooth lisse	14	34	enveloping enveloppant	20	22
	high haut	15	34	variation variation	20	22
	piano piano (Musical term)	15	34	vibrer vibrating	20	22
	clear clair	15	34	stable stable	20	22

W/I : Word/Interviewee frequency. * words that communicate different concepts in French language but have the same translation in English.

Table 3 :

 3 Categories of description strategies built for the coding of the transcripts. most exclusively described through spectral features, while round is defined both spectrally and temporally.

		100	bright
			warm
	% in population	40 60 80	round rough
		20
		0	categories Sound Dyn Spec Temp Ex Source CMC Matter Effect Affect

VAME : Verbal Attribute Magnitude Estimation

http://www.vsl.co.at

http://atilf.atilf.fr/