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Compact Disc Digital Audio

Compact Disc Digital Audio (CDDA or CD-DA), also known as Digital Audio Compact Disc or simply as Audio CD, is the standard format for audio compact discs. The standard is defined in the Red Book, one of a series of Rainbow Books (named for their binding colors) that contain the technical specifications for all CD formats. CDDA utilizes pulse-code modulation (PCM) and uses a 44,100 Hz sampling frequency and 16-bit resolution, and was originally specified to store up to 74 minutes of stereo audio per disc.

The first commercially available audio CD player, the Sony CDP-101, was released in October 1982 in Japan. The format gained worldwide acceptance in 1983–84, selling more than a million CD players in those two years, to play 22.5 million discs. In the music industry, audio CDs have been generally sold as either a CD single (now largely dormant), or as full-length albums, the latter of which has been more commonplace since the 2000s.

Beginning in the 2000s, CDs were increasingly being replaced by other forms of digital storage and distribution, with the result that by 2010 the number of audio CDs being sold in the U.S. had dropped about 50% from their peak; however, they remained one of the primary distribution methods for the music industry. In the 2010s, revenues from digital music services, such as iTunes, Spotify, and YouTube, matched those from physical format sales for the first time. According to the RIAA's midyear report in 2020, phonograph record revenues surpassed those of CDs in the U.S. for the first time since the 1980s, whereas in Japan the CD remains the premier music format and revenues have grown in 2022, and in Germany it outsold other physical formats at least fourfold in 2022.

History
The optophone, first presented in 1931, was an early device that used light for both recording and playback of sound signals on a transparent photograph. More than thirty years later, American inventor James T. Russell has been credited with inventing the first system to record digital media on a photosensitive plate. Russell's patent application was filed in 1966, and he was granted a patent in 1970. Following litigation, Sony and Philips licensed Russell's patents for recording in 1988. It is debatable whether Russell's concepts, patents, and prototypes instigated and in some measure influenced the compact disc's design.

The compact disc is an evolution of LaserDisc technology, where a focused laser beam is used that enables the high information density required for high-quality digital audio signals. Unlike the prior art by Optophonie and James Russell, the information on the disc is read from a reflective layer using a laser as a light source through a protective substrate. Prototypes were developed by Philips and Sony independently in the late 1970s. Although originally dismissed by Philips Research management as a trivial pursuit, the CD became the primary focus for Philips as the LaserDisc format struggled. In 1979, Sony and Philips set up a joint task force of engineers to design a new digital audio disc. After a year of experimentation and discussion, the Red Book CD-DA standard was published in 1980. After their commercial release in 1982, compact discs and their players were extremely popular. Despite costing up to $1,000, over 400,000 CD players were sold in the United States between 1983 and 1984. By 1988, CD sales in the United States surpassed those of vinyl LPs, and by 1992 CD sales surpassed those of prerecorded music cassette tapes. The success of the compact disc has been credited to the cooperation between Philips and Sony, which together agreed upon and developed compatible hardware. The unified design of the compact disc allowed consumers to purchase any disc or player from any company and allowed the CD to dominate the at-home music market unchallenged.

Digital audio laser-disc prototypes
In 1974, Lou Ottens, director of the audio division of Philips, started a small group to develop an analog optical audio disc with a diameter of 20 cm and a sound quality superior to that of the vinyl record. However, due to the unsatisfactory performance of the analog format, two Philips research engineers recommended a digital format in March 1974. In 1977, Philips then established a laboratory with the mission of creating a digital audio disc. The diameter of Philips's prototype compact disc was set at 11.5 cm, the diagonal of an audio cassette.

Heitaro Nakajima, who developed an early digital audio recorder within Japan's national public broadcasting organization, NHK, in 1970, became general manager of Sony's audio department in 1971. In 1973, his team developed a digital PCM adaptor that made audio recordings using a Betamax video recorder. After this, in 1974 the leap to storing digital audio on an optical disc was easily made. Sony first publicly demonstrated an optical digital audio disc in September 1976. A year later, in September 1977, Sony showed the press a 30 cm disc that could play an hour of digital audio (44,100 Hz sampling rate and 16-bit resolution) using modified frequency modulation encoding. In September 1978, the company demonstrated an optical digital audio disc with a 150-minute playing time, 44,056 Hz sampling rate, 16-bit linear resolution, and cross-interleaved error correction code—specifications similar to those later settled upon for the standard compact disc format in 1980. Technical details of Sony's digital audio disc were presented during the 62nd AES Convention, held on 13–16 March 1979, in Brussels. Sony's AES technical paper was published on 1 March 1979. A week later, on 8 March, Philips publicly demonstrated a prototype of an optical digital audio disc at a press conference called "Philips Introduce Compact Disc" in Eindhoven, Netherlands. Sony executive Norio Ohga, later CEO and chairman of Sony, and Heitaro Nakajima were convinced of the format's commercial potential and pushed further development despite widespread skepticism.

Collaboration and standardization
In 1979, Sony and Philips set up a joint task force of engineers to design a new digital audio disc. Led by engineers Kees Schouhamer Immink and Toshitada Doi, the research pushed forward laser and optical disc technology. After a year of experimentation and discussion, the task force produced the Red Book CD-DA standard. First published in 1980, the standard was formally adopted by the IEC as an international standard in 1987, with various amendments becoming part of the standard in 1996.

Philips coined the term compact disc in line with another audio product, the Compact Cassette, and contributed the general manufacturing process, based on video LaserDisc technology. Philips also contributed eight-to-fourteen modulation (EFM), while Sony contributed the error-correction method, CIRC, which offers resilience to defects such as scratches and fingerprints.

The Compact Disc Story, told by a former member of the task force, gives background information on the many technical decisions made, including the choice of the sampling frequency, playing time, and disc diameter. The task force consisted of around 6 persons, though according to Philips, the compact disc was "invented collectively by a large group of people working as a team".

Initial launch and adoption
Early milestones in the launch and adoption of the format included:
 * The first test pressing was of a recording of Richard Strauss's An Alpine Symphony, recorded December 1–3, 1980 and played by the Berlin Philharmonic and conducted by Herbert von Karajan, who had been enlisted as an ambassador for the format in 1979.
 * The world presentation took place during the Salzburg Easter Festival on 15 April 1981, at a press conference of Akio Morita and Norio Ohga (Sony), Joop van Tilburg (Philips), and Richard Busch (PolyGram), in the presence of Karajan who praised the new format.
 * The first public demonstration was on the BBC television programme Tomorrow's World in 1981, when the Bee Gees' album Living Eyes (1981) was played.
 * The first commercial compact disc was produced on 17 August 1982, a 1979 recording of Chopin waltzes performed by Claudio Arrau.
 * The first 50 titles were released in Japan on 1 October 1982, the first of which was a re-release of the Billy Joel album 52nd Street.
 * The first CD played on BBC Radio was in October 1982 on BBC Radio Scotland (Jimmy Mack programme, Followed by Ken Bruce and Eddie Mair all BBC Scotland), with the first CD played on UK independent radio station shortly after (Radio Forth, Jay Crawford Show). The CD was the Dire Straits album Love Over Gold.
 * The Japanese launch was followed on 14 March 1983 by the introduction of CD players and discs to Europe and North America where CBS Records released sixteen titles.

The first artist to sell a million copies on CD was Dire Straits, with their 1985 album Brothers in Arms. One of the first CD markets was devoted to reissuing popular music whose commercial potential was already proven. The first major artist to have their entire catalog converted to CD was David Bowie, whose first fourteen studio albums of (then) sixteen were made available by RCA Records in February 1985, along with four greatest hits albums; his fifteenth and sixteenth albums had already been issued on CD by EMI Records in 1983 and 1984, respectively. On 26 February 1987, the first four UK albums by the Beatles were released in mono on compact disc.

The growing acceptance of the CD in 1983 marks the beginning of the popular digital audio revolution. It was enthusiastically received, especially in the early-adopting classical music and audiophile communities, and its handling quality received particular praise. As the price of players gradually came down, and with the introduction of the portable Discman, the CD began to gain popularity in the larger popular and rock music markets. With the rise in CD sales, pre-recorded cassette tape sales began to decline in the late 1980s; CD sales overtook cassette sales in the early 1990s. In 1988, 400 million CDs were manufactured by 50 pressing plants around the world.

Further development

Early CD players employed binary-weighted digital-to-analog converters (DAC), which contained individual electrical components for each bit of the DAC. Even when using high-precision components, this approach was prone to decoding errors. Another issue was jitter, a time-related defect. Confronted with the instability of DACs, manufacturers initially turned to increasing the number of bits in the DAC and using several DACs per audio channel, averaging their output. This increased the cost of CD players but did not solve the core problem.

A breakthrough in the late 1980s culminated in development of the 1-bit DAC, which converts high-resolution low-frequency digital input signal into a lower-resolution high-frequency signal that is mapped to voltages and then smoothed with an analog filter. The temporary use of a lower-resolution signal simplified circuit design and improved efficiency, which is why it became dominant in CD players starting from the early 1990s. Philips used a variation of this technique called pulse-density modulation (PDM), while Matsushita (now Panasonic) chose pulse-width modulation (PWM), advertising it as MASH, which is an acronym derived from their patented Multi-stAge noiSe-sHaping PWM topology.

The CD was primarily planned as the successor to the vinyl record for playing music, rather than as a data storage medium. However, CDs have grown to encompass other applications. In 1983, following the CD's introduction, Immink and Joseph Braat presented the first experiments with erasable compact discs during the 73rd AES Convention. In June 1985, the computer-readable CD-ROM (read-only memory) and, in 1990, recordable CD-R discs were introduced. Recordable CDs became an alternative to tape for recording and distributing music and could be duplicated without degradation in sound quality.

Other newer video formats such as DVD and Blu-ray use the same physical geometry as CD, and most DVD and Blu-ray players are backward compatible with audio CDs.

Peak
CD sales in the United States peaked by 2000. By the early 2000s, the CD player had largely replaced the audio cassette player as standard equipment in new automobiles, with 2010 being the final model year for any car in the United States to have a factory-equipped cassette player.

Two new formats were marketed in the 2000s designed as successors to the CD: the Super Audio CD (SACD) and DVD-Audio. However neither of these were adopted partly due to increased relevance of digital (virtual) music and the apparent lack of audible improvements in audio quality to most human ears. These effectively extended the CD's longetivity in the music market.

Decline
With the advent and popularity of Internet-based distribution of files in lossy-compressed audio formats such as MP3, sales of CDs began to decline in the 2000s. For example, between 2000 and 2008, despite overall growth in music sales and one anomalous year of increase, major-label CD sales declined overall by 20%. Despite rapidly declining sales year-over-year, the pervasiveness of the technology lingered for a time, with companies placing CDs in pharmacies, supermarkets, and filling station convenience stores to target buyers less likely to be able to use Internet-based distribution. In 2012, CDs and DVDs made up only 34% of music sales in the United States. By 2015, only 24% of music in the United States was purchased on physical media, two thirds of this consisting of CDs; however, in the same year in Japan, over 80% of music was bought on CDs and other physical formats. In 2018, U.S. CD sales were 52 million units—less than 6% of the peak sales volume in 2000. In the UK, 32 million units were sold, almost 100 million fewer than in 2008. In 2018, Best Buy announced plans to decrease their focus on CD sales, however, while continuing to sell records, sales of which are growing during the vinyl revival.

During the 2010s, the increasing popularity of solid-state media and music streaming services caused automakers to remove automotive CD players in favor of minijack auxiliary inputs, wired connections to USB devices and wireless Bluetooth connections. Automakers viewed CD players as using up valuable space and taking up weight which could be reallocated to more popular features, like large touchscreens. By 2021, only Lexus and General Motors were still including CD players as standard equipment with certain vehicles.

Current status
CDs continued to be strong in some markets such as Japan where 132 million units were produced in 2019.

The decline in CD sales has slowed in recent years; in 2021, CD sales increased in the US for the first time since 2004, with Axios citing its rise to "young people who are finding they like hard copies of music in the digital age". It came at the same time as both vinyl and cassette reached sales levels not seen in 30 years. The RIAA reported that CD revenue made a dip in 2022, before increasing again in 2023 and overtook downloading for the first time in over a decade.

In the US, 33.4 million CD albums were sold in the year 2022. In France in 2023, 10.5 million CDs were sold, almost double that of vinyl, but both of them represented generated 12% each of the French music industry revenues.

Awards and accolades
Sony and Philips received praise for the development of the compact disc from professional organizations. These awards include:
 * Technical Grammy Award for Sony and Philips, 1998.
 * IEEE Milestone award, 2009, for Philips alone with the citation: "On 8 March 1979, N.V. Philips' Gloeilampenfabrieken demonstrated for the international press a Compact Disc Audio Player. The demonstration showed that it is possible by using digital optical recording and playback to reproduce audio signals with superb stereo quality. This research at Philips established the technical standard for digital optical recording systems."

Standard
The Red Book specifies the physical parameters and properties of the CD, the optical parameters, deviations and error rate, modulation system (eight-to-fourteen modulation, EFM) and error correction facility (cross-interleaved Reed–Solomon coding, CIRC), and the eight subcode channels. These parameters are common to all compact discs and used by all logical formats: audio CD, CD-ROM, etc. The standard also specifies the form of digital audio encoding.

The first edition of the Red Book was released in 1980 by Philips and Sony; it was adopted by the Digital Audio Disc Committee and ratified by the International Electrotechnical Commission (IEC) Technical Committee 100 as an international standard in 1987 with the reference IEC 60908. The second edition of IEC 60908 was published in 1999 and it replaces the first edition, amendment 1 (1992) and the corrigendum to amendment 1. The IEC 60908 however does not contain all the information for extensions that is available in the Red Book, such as the details for CD-Text, CD+G and CD+EG.

The standard is not freely available and must be licensed. It is available from Philips and the IEC. , Philips outsources licensing of the standard to Adminius, which charges US$100 for the Red Book, plus US$50 each for the Subcode Channels R-W and CD Text Mode annexes.

Audio format
The audio contained in a CD-DA consists of two-channel signed 16-bit LPCM sampled at 44,100 Hz and written as a little-endian interleaved stream with left channel coming first.

The sampling rate is adapted from that attained when recording digital audio on videotape with a PCM adaptor, an earlier way of storing digital audio. An audio CD can represent frequencies up to 22.05 kHz, the Nyquist frequency of the 44.1 kHz sample rate.

There was a long debate over the use of 16-bit (Sony) or 14-bit (Philips) quantization, and 44,056 or 44,100 samples/s (Sony) or approximately 44,000 samples/s (Philips). When the Sony/Philips task force designed the Compact Disc, Philips had already developed a 14-bit D/A converter (DAC), but Sony insisted on 16-bit. In the end Sony won, so 16 bits and 44.1 kilosamples per second prevailed. Philips found a way to produce 16-bit quality using its 14-bit DAC by using four times oversampling.

Some early CDs were mastered with pre-emphasis, an artificial boost of high audio frequencies. The pre-emphasis improves the apparent signal-to-noise ratio by making better use of the channel's dynamic range. On playback, the player applies a de-emphasis filter to restore the frequency response curve to an overall flat one. Pre-emphasis time constants are 50 μs and 15 μs (9.49 dB boost at 20 kHz), and a binary flag in the disc subcode instructs the player to apply de-emphasis filtering if appropriate. Playback of such discs in a computer or ripping to WAV files typically does not take into account the pre-emphasis, so such files play back with an incorrect frequency response. FFmpeg has a filter to remove (or apply) the pre-emphasis in order to create standard WAV files, or to create CDs with pre-emphasis.

Four-channel, or quadraphonic, supported was originally intended to be included in CD-DA. The Red Book specification briefly mentioned a four-channel mode in its June 1980, September 1983, and November 1991 editions. On the first page, it lays out the "Main parameters" of the CD system, including: "Number of channels: 2 and/or 4 simultaneously[*] sampled." The footnote says, "In the case of more than two channels the encoder and decoder diagrams have to be adapted."

In reality, however, the underspecified "four-channel" mode was dropped from the CD standard when it was adopted by the International Electrotechnical Commission and became IEC 908:1987, and later IEC 60908:1999. Since the behavior of the "four-channel" or "Broadcasting use" bit was never specified by either CD standard, no mass-marketed discs have attempted to use the Red Book's four-channel mode, and no players have purported to implement it.

Storage capacity and playing time
The creators of the CD originally aimed at a playing time of 60 minutes with a disc diameter of 100 mm (Sony) or 115 mm (Philips). Sony vice-president Norio Ohga suggested extending the capacity to 74 minutes to accommodate the recording of Wilhelm Furtwängler conducting Ludwig van Beethoven's Ninth Symphony at the 1951 Bayreuth Festival. The additional 14-minute playing time required increasing disc diameter. Kees Schouhamer Immink, Philips' chief engineer, however, denies this, claiming that the increase was motivated by technical considerations and that even after the increase in size, the Furtwängler recording would not have fit onto one of the earliest CDs.

According to a Sunday Tribune interview, the story is slightly more involved. In 1979, Philips owned PolyGram, one of the world's largest music distributors. PolyGram had set up a large experimental CD plant in Hannover, Germany, which could produce huge numbers of CDs having a diameter of 115 mm. Sony did not yet have such a facility. If Sony had agreed on the 115-mm disc, Philips would have had a significant competitive edge in the market. The long playing time of Beethoven's Ninth Symphony imposed by Ohga was used to push Philips to accept 120 mm, so that Philips' PolyGram lost its edge on disc fabrication.

The 74-minute playing time of a CD, which is longer than the 22 minutes per side typical of long-playing (LP) vinyl albums, was often used to the CD's advantage during the early years when CDs and LPs vied for commercial sales. CDs would often be released with one or more bonus tracks, enticing consumers to buy the CD for the extra material. However, attempts to combine double LPs onto one CD occasionally resulted in the opposite situation in which the CD would instead offer less audio than the LP. One such example was with DJ Jazzy Jeff & The Fresh Prince's double album He's the DJ, I'm the Rapper, in which initial CD releases of the album had multiple tracks edited down for length to fit on a single disc; recent CD reissues package the album across two discs as a result. The emergence of 80-minute CDs allowed for some double albums that were previously edited for length, e.g. 1999 by Prince, or packaged as double CDs, e.g. Tommy by the Who, to be re-released on a single disc.

Playing times beyond 74 minutes are achieved by decreasing track pitch (the distance separating the track as it spirals the disc). However, most players can still accommodate the more closely spaced data if it is still within Red Book tolerances. Manufacturing processes used in the final years of CD technology allowed an audio CD to contain up to 82 minutes (variable from one replication plant to another) without requiring the content creator to sign a waiver releasing the plant owner from responsibility if the CD produced is marginally or entirely unreadable by some playback equipment. In this final practice, maximum CD playing time crept higher by reducing minimum engineering tolerances.

Data encoding
Each audio sample is a signed 16-bit two's complement integer, with sample values ranging from −32768 to +32767. The source audio data is divided into frames, containing twelve samples each (six left and six right samples, alternating), for a total of 192 bits (24 bytes) of audio data per frame.

This stream of audio frames, as a whole, is then subjected to CIRC encoding, which segments and rearranges the data and expands it with error correction codes in a way that allows occasional read errors to be detected and corrected. CIRC encoding interleaves the audio frames throughout the disc over several consecutive frames so that the information will be more resistant to burst errors. Therefore, a physical frame on the disc will actually contain information from multiple logical audio frames. This process adds 64 bits of error correction data to each frame. After this, 8 bits of subcode or subchannel data are added to each of these encoded frames, which is used for control and addressing when playing the CD.

CIRC encoding plus the subcode byte generate 33-bytes long frames, called "channel-data" frames. These frames are then modulated through eight-to-fourteen modulation (EFM), where each 8-bit word is replaced with a corresponding 14-bit word designed to reduce the number of transitions between 0 and 1. This reduces the density of physical pits on the disc and provides an additional degree of error tolerance. Three "merging" bits are added before each 14-bit word for disambiguation and synchronization. In total there are 33 × (14 + 3) = 561 bits. A 27-bit word (a 24-bit pattern plus 3 merging bits) is added to the beginning of each frame to assist with synchronization, so the reading device can locate frames easily. With this, a frame ends up containing 588 bits of "channel data" (which are decoded to only 192 bits of music).

The frames of channel data are finally written to disc physically in the form of pits and lands, with each pit or land representing a series of zeroes, and with the transition points—the edge of each pit—representing a 1. A Red Book-compatible CD-R has pit-and-land-shaped spots on a layer of organic dye instead of actual pits and lands; a laser creates the spots by altering the reflective properties of the dye.

Due to the weaker error correction sector structure used on audio CDs and video CDs (Mode 2 Form 2) than on data discs (Mode 1 or Mode 2 Form 1), C2 errors are not correctable and signify data loss. Even with uncorrectable errors, a compact disc player interpolates the data loss with the aim of making the damage unhearable.

Data structure
The audio data stream in an audio CD is continuous, but has three parts. The main portion, which is further divided into playable audio tracks, is the program area. This section is preceded by a lead-in track and followed by a lead-out track. The lead-in and lead-out tracks encode only silent audio, but all three sections contain subcode data streams.

The lead-in's subcode contains repeated copies of the disc's Table of Contents (TOC), which provides an index of the start positions of the tracks in the program area and lead-out. The track positions are referenced by absolute timecode, relative to the start of the program area, in MSF format: minutes, seconds, and fractional seconds called frames. Each timecode frame is one seventy-fifth of a second, and corresponds to a block of 98 channel-data frames—ultimately, a block of 588 pairs of left and right audio samples. Timecode contained in the subchannel data allows the reading device to locate the region of the disc that corresponds to the timecode in the TOC. The TOC on discs is analogous to the partition table on hard drives. Nonstandard or corrupted TOC records are abused as a form of CD/DVD copy protection, in e.g. the key2Audio scheme.

Tracks
The largest entity on a CD is called a track. A CD can contain up to 99 tracks (including a data track for mixed mode discs). Each track can in turn have up to 100 indexes, though players which still support this feature have become rarer over time. The vast majority of songs are recorded under index 1, with the pregap being index 0. Sometimes hidden tracks are placed at the end of the last track of the disc, often using index 2 or 3, or using the pregap as index 0 (this latter usage will result in the track playing as the time counter counts down to time 0:00 at the start of the track, index 1.) This is also the case with some discs offering "101 sound effects", with 100 and 101 being indexed as two and three on track 99. The index, if used, is occasionally put on the track listing as a decimal part of the track number, such as 99.2 or 99.3. (Information Society's Hack was one of very few CD releases to do this, following a release with an equally obscure CD+G feature.) The track and index structure of the CD were carried forward to the DVD format as title and chapter, respectively.

Tracks, in turn, are divided into timecode frames (or sectors), which are further subdivided into channel-data frames.

Frames and timecode frames
The smallest entity in a CD is a channel-data frame, which consists of 33 bytes and contains six complete 16-bit stereo samples: 24 bytes for the audio (two bytes × two channels × six samples = 24 bytes), eight CIRC error-correction bytes, and one subcode byte. As described in the "Data encoding" section, after the EFM modulation the number of bits in a frame totals 588.

On a Red Book audio CD, data is addressed using the MSF scheme, with timecodes expressed in minutes, seconds and another type of frames (mm:ss:ff), where one frame corresponds to 1/75 of a second of audio: 588 pairs of left and right samples. This timecode frame is distinct from the 33-byte channel-data frame described above, and is used for time display and positioning the reading laser. When editing and extracting CD audio, this timecode frame is the smallest addressable time interval for an audio CD; thus, track boundaries only occur on these frame boundaries. Each of these structures contains 98 channel-data frames, totaling 98 × 24 = 2,352 bytes of music. The CD is played at a speed of 75 frames (or sectors) per second, thus 44,100 samples or 176,400 bytes per second.

In the 1990s, CD-ROM and related Digital Audio Extraction (DAE) technology introduced the term sector to refer to each timecode frame, with each sector being identified by a sequential integer number starting at zero, and with tracks aligned on sector boundaries. An audio CD sector corresponds to 2,352 bytes of decoded data. The Red Book does not refer to sectors, nor does it distinguish the corresponding sections of the disc's data stream except as "frames" in the MSF addressing scheme.

The following table shows the relation between tracks, timecode frames (sectors) and channel-data frames:

Bit rate
The audio bit rate for a Red Book audio CD is 1,411,200 bits per second (1,411 kbit/s) or 176,400 bytes per second; 2 channels × 44,100 samples per second per channel × 16 bits per sample. Audio data coming in from a CD is contained in sectors, each sector being 2,352 bytes, and with 75 sectors containing 1 second of audio. For comparison, the bit rate of a "1×" CD-ROM is defined as 2,048 bytes per sector × 75 sectors per second = 153,600 bytes per second. The remaining 304 bytes in a sector are used for additional data error correction.

Data access from computers
Unlike on a DVD or CD-ROM, there are no "files" on a Red Book audio CD; there is only one continuous stream of LPCM audio data, and a parallel, smaller set of 8 subcode data streams. Computer operating systems, however, may provide access to an audio CD as if it contains files. For example, Windows represents the CD's Table of Contents as a set of Compact Disc Audio track (CDA) files, each file containing indexing information, not audio data. By contrast however, Finder on macOS presents the CD's content as an actual set of files, with the AIFF-extension, which can be copied directly, randomly and individually by track as if it were actual files. In reality, macOS performs its own as-needed-rips in the background completely transparent to the user. The copied tracks are fully playable and editable on the user's computer.

In a process called ripping, digital audio extraction software can be used to read CD-DA audio data and store it in files. Common audio file formats for this purpose include WAV and AIFF, which simply preface the LPCM data with a short header; FLAC, ALAC, and Windows Media Audio Lossless, which compress the LPCM data in ways that conserve space yet allow it to be restored without any changes; and various lossy, perceptual coding formats like MP3, AAC, and Opus, which modify and compress the audio data in ways that irreversibly change the audio, but that exploit features of human hearing to make the changes difficult to discern.

Format variations
Recording publishers have created CDs that violate the Red Book standard. Some do so for the purpose of copy prevention, using systems like Copy Control. Some do so for extra features such as DualDisc, which includes both a CD layer and a DVD layer whereby the CD layer is much thinner, 0.9 mm, than required by the Red Book, which stipulates a nominal 1.2 mm, but at least 1.1 mm. Philips and many other companies have stated that including the Compact Disc Digital Audio logo on such non-conforming discs may constitute trademark infringement.

Super Audio CD was a standard published in 1999 that aimed to provide better audio quality than CDs. DVD-Audio emerged at around the same time. Both formats were designed to feature audio of higher fidelity by using a higher sampling rate and DVD media. Neither format was widely accepted.

Copyright issues
There have been moves by the recording industry to make audio CDs (Compact Disc Digital Audio) unplayable on computer CD-ROM drives, to prevent the copying of music. This is done by intentionally introducing errors onto the disc that the embedded circuits on most stand-alone audio players can automatically compensate for, but which may confuse CD-ROM drives. Consumer rights advocates as of October 2001 pushed to require warning labels on compact discs that do not conform to the official Compact Disc Digital Audio standard (often called the Red Book) to inform consumers which discs do not permit full fair use of their content.

In 2005, Sony BMG Music Entertainment was criticized when a copy protection mechanism known as Extended Copy Protection (XCP) used on some of their audio CDs automatically and surreptitiously installed copy-prevention software on computers (see Sony BMG copy protection rootkit scandal). Such discs are not legally allowed to be called CDs or Compact Discs because they break the Red Book standard governing CDs, and Amazon.com for example describes them as "copy protected discs" rather than "compact discs" or "CDs".

title: Compact Disc Digital Audio


text:
Talk:Acre, Israel

Image
The image for 'Acre' used to be massive. I attempted to minimize it, but have accidentally effaced it altogether somehow (although the code remains in the source). For the time being, no picture is better than a gargantuan one, but I'd appreciate someone sorting this out.

CharlieRCD (talk) —Preceding comment was added at 21:58, 25 March 2008 (UTC)

old talk (may be unsigned, undated and un-organized

 * (still predominantly a 1911 text - needs lots of revisions; this land is currently held by Israel in violation of United Nations resolutions.

How come, Akko is well inside the Green Line (242 does not apply), its inhabitants (Jewish and Arab alike) are Israeli citizens, what's the issue here? --Uriyan

Uriyan is right here. There is no question that Acre, a coastal town in the Western Galilee, is within the boundaries of pre-1967 Israel. Danny

I worked through the page and did major copy edits and divided into topics and sub-topics. I also replaced the information about Akko's wall with a correct one and added some links with the history of Akko, as well as the official site of the Old Acre Developmemt Company.

Currently, the part of history is need more works since its laking many details. Also, we need to relate to the modern city of Akko (outside the walls). MathKnight 15:18, 30 Jul 2004 (UTC)

City of Acre
A google search on English pages returns: Restricting the search to Palistine and Israel
 * about 5,090,000 English pages for City of Acre
 * about 23,400 English pages for City of Akko
 * about 27,900 English pages for Akko palestine
 * about 27,000 English pages for Akko Israel
 * about 739,000 English pages for Acre palestine
 * about 413,000 English pages for Acre Israel.

It is not archaic to us it in English eg: Original Author which was not a stub starts: "Acre, Akka, or St Jean D'Acre",
 * http://whc.unesco.org/pg.cfm?cid=31&id_site=1042

So why is this article not under "Acre (city)" or some other title? PBS 11:47, 19 May 2005 (UTC)

 * This one is a little sticky, because while there is plenty of precedent for using the "English translation" of a local name, that "English translation" is ambiguous with a very common word. All of the options are unpalatable, "Akko" seems simplest. Google results are not very meaningful, because hard to exclude uses of "acre" the unit of measurement. Stan 19:20, 19 May 2005 (UTC)

Even if the page is not moved, the first name in the introduction should be "Acre" as that is the common English name. It should also be used throughout the rest of the article. PBS 13:52, 20 May 2005 (UTC)

Ok...so why is it now at "City of Acre"? "Acre (city)" is the most appropriately disambiguated title. "City of Acre" makes no sense. I notice, Philip, that you are even changing links to the "city" link, which redirects here... Adam Bishop 04:06, 25 July 2005 (UTC)

 * Because I thought it was a better name and then changed my mind but messed up the page move to "Acre (city)" locking the page. But on reflection I am not sure that "Acre (city)" is better than City of Acre. I am agnostic on either name as a disambiguation name for the city of Acre.  PBS 21:50, 29 July 2005 (UTC)

 * Anyone still interested in this page move? I would propose simply "Acre", unless it's inappropriate or would cause a disambiguation problem. IMO this reflects the city's historical importance best, notwithstanding the above page numbers. Wally 16:03, 17 January 2006 (UTC)

Which Herod?
The article says:
 * Here Herod built a gymnasium

Which Herod is meant? Gdr 21:12, 11 July 2005 (UTC) I was just wondering if anyone could add anything About Bahaullah. He is believed by the Bahais to be a prophet of God and I believe sent out various messages to the various leaders of countries at the time in Akka. Sorry Im not that informed on the subject but if anyone has any information, I think it may be a welcome addition to the cities history.

Jezzar Pasha
There appears to be an article about this fellow, as Cezzar Ahmet. It looks like there should just be a redirect or something to the unwritten Jezzar Pasha Mdanziger 21:48, 1 March 2006 (UTC)

Knights of Templar
There is too much written here about the Hospitaller's and their role in Acre, which is significantly dwarfed in reality by the role of the Knights Templar. —The preceding unsigned comment was added by 67.4.139.79 (talk • contribs) 19:46, 5 March 2006 (UTC)

Bahá'u'lláh
I can't belive he's not mentioned in this article..... COME ON.....

Pure inuyasha 01:28, 27 May 2006 (UTC)
 * done. Thanks for suggesting it. -- Jeff3000 03:19, 5 June 2006 (UTC)

Location of "infobox"
I moved the infobox out of the lead section because 1) it is ugly 2) the purpose of the lead section (see Lead section) is to draw reader attention into the article and a picture is much more stylistically pleasing and inviting than a bland wall of statistics and 3) there is no rule that says infoboxes have to be in the lead section. In fact, many infoboxen have incorporated pictures into them -- with the picture coming first! It doesn't matter where the infobox goes in the article but it shouldn't be in the lead section when there are perfectly good pictures that can go there. In addition, per the MoS on image placement, don't stack images (or boxes) one on top of each other, they should be "laddered" left/right, there are even "nag tamplates" for articles that do that.  -- Stbalbach 05:17, 25 July 2006 (UTC)
 * Regardless of that, it absolutely does not belong in the section "The Greek and Roman periods". If there were a demographics section you could probably put it there, but for now I think we should put it below the image of the city. --PiMaster3 12:35, 26 July 2006 (UTC)
 * I'm willing to compromise with that but the template won't position correctly so I put it as the first thing in the first section. -- Stbalbach 13:42, 26 July 2006 (UTC)
 * I really believe that the infobox should be at the top, like all the country pages. If there is no picture option in the infobox template, that's a problem with the template, and not with this page.  I'll move the infobox back to the top. -- Jeff3000 16:25, 26 July 2006 (UTC)
 * Why don't you stick one of those pictures into the infobox? There are two pics right at the top... Adam Bishop 19:57, 26 July 2006 (UTC)
 * That would be too easy. Ok so now the only remaining problem is the template has no "image description" field so the image has lost some context. I'll post on the template page for a mod unless someone else has another idea. -- Stbalbach 20:11, 26 July 2006 (UTC)

Ongoign war incidents
Regarding this entry:
 * During the 2006 Israel-Lebanon conflict, Hezbollah launched rocket attacks on Acre, with two rockets landing. The rocket attacks led to Israel's Home Front Command to order the residents of Acre to stay in protective spaces.

See Talk:Tiberias for reason for removal from the article. -- Stbalbach 13:24, 15 August 2006 (UTC)

Modern pronounciation?
I noticed it's not mentioned in the first line.--NEMT 13:38, 29 January 2007 (UTC)

We might want to get a recording of a pronunciation. I've heard it pronounced (and by "heard", what I really mean is "played Assassin's Creed - that's DEFINITELY a good source) as basically "Ak", and then just a hint of a second syllable with a "Kuh". 82.19.71.40 (talk) 23:15, 13 August 2008 (UTC)

 * I've seen earlier English spellings where it's quite obvious the pronunciation is something like 'Akk-ker' - the modern 'Ache-er' mispronunciation (as in the unit of land area measure, the acre}, is, I think, relatively recent, and certainly wouldn't have been use by anyone familiar with the region. Ian Dunster (talk) 10:53, 7 September 2008 (UTC)
 * It is not Akker but Akko.--Gilabrand (talk) 05:31, 8 September 2008 (UTC)

Lieutenant Petit
Do we want to keep the paragraph on Lieutenant Petit? It is unsubstantiated hearsay that has obvious credibility problems on a number of fronts - also the person who originally added it to this article mis-represented what the source said - I had to find the source and re-write the paragraph so it was accurate. What does it add to this article, all it shows is a Palestinian made un-proven claims against the Israeli army of atrocities - we could write an entire Encyclopedia of people who make claims like that. -- Stbalbach 15:56, 19 February 2007 (UTC)
 * Makes sense; go ahead and remove it. -- Jeff3000 16:31, 19 February 2007 (UTC)

Requested move

 * The following discussion is an archived discussion of the . Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

NO CONSENSUS to move page, per discussion below. I think good cases can be made for both sides, but without a compelling reason, we try to avoid names from one controversial name to another. The consensus over thousands of geographic articles is to use the name most commonly used in English-language sources. Searches for "Acre Israel" and "Akko Israel are neck and neck, but when you omit the quotation marks, the difference is marked: Acre vs Akko, with not a false positive in the first 50 hits. It may be the case that "Akko" is supplanting "Acre" in modern usage, and that English language sources will shift towards the more historically accurate spelling. At that time, if we've got the same naming conventions, we'll move the article. -GTBacchus(talk) 03:47, 23 March 2007 (UTC)
 * Which spelling is "historically more accurate" is another question; "Acre" has been used in English for quite some time; probably since the 13th century. Septentrionalis PMAnderson 21:55, 23 March 2007 (UTC)

Acre, Israel → Akko — this wikipedia article, by the name of acre, is reffering to the Israeli city of Akko - this city has been by the name Akko since even before the days of the Kingdom of Israel (i.e. pre-2000BC) and it is belived that Abraham went past it on his way from nowdays southern syria to Shchem (his path is illustrated by a mosaic in a beit knesset there) - the city only had it's name changed to acre after the muslim invasion (post-7th century AD) and the current international name is Akko - therefore i believe the correct name for the article is by the international Israeli name. Jaakobou 17:39, 17 March 2007 (UTC)

Survey

 * Add  # Support   or   # Oppose   on a new line in the appropriate section followed by a brief explanation, then sign your opinion using ~ .  Please remember that this survey is not a vote, and please provide an explanation for your recommendation.

Survey - in support of the move

 * 1) Support - ask an israeli about "acre" and he wouldn't have a clue to what you're talking about - "akko" is the current national and international name for the city. city of akko - on hebrew wiki - also, there are the notes i've given at the into to the reasoning which includes Abraham day name of city.akko, old city last note: just because some people are confused, doesn't change the current name of the city... for your pleasure: interactive touring map of israel - akko is up north, above haifa. Jaakobou 17:54, 17 March 2007 (UTC)
 * 2) Very Strongly Support - Akko is the official Israeli state name of the city. It is recognized internationally on web sites such as the US Dept of State and United Nations and in many published books in English, there does not appear to be any controversy or lack of recognition of the name Akko. Of course some of those same web sites also have Acre, and Acre is certainly widely known, so the question is, use the historical name Acre or the present-day name Akko (current since the 1950s?). The opening sentence should be: "Akko (historically Acre) is a city.." which is precise and accurate, but would necessitate renaming the article to Akko .. it also seems common to refer to the historical city as "Old city of Acre" which can be done within the article, along with a history of the name changes. Finally, since we have re-directs, there is no problem with users finding the right article, although when linking from other Wikipedia article, the historical name Acre is used when discussing in a historical context (such as in articles about the Crusades). This situation is similar to St. Petersburg and Leningrad. The city was founded originally as St. Petersburg. It then was changed to Leningrad. Then later changed back to St. Petersburg (with a Petrograd in there for a time). -- Stbalbach 13:38, 18 March 2007 (UTC)
 * 3) Support - I read all the arguments, and Akko is also the old name and the new name. Seems Acre is something left as a nickname from the British mandate and times, they are a changin'. -MouseWarrior

Survey - in opposition to the move

 * 1) Oppose - Ask anyone except an Israeli about "Akko" and s/he wouldn't have a clue what you were talking about. Acre is the widely understood, internationally accepted name for the city. Wikipedia has pages on Jerusalem, not Yerushalayim, Jaffa not Yafo, Safed not Tzfat, Tiberias not Tverya and many other examples. Similarly, articles are about Hebron, not Al-Khalil, Jericho not Ariha and others.
 * This does not only apply to contentious Middle East issues. There is an article on Rome, not Roma; Moscow not Moskva; Prague, not Praha.
 * Jaakobou's reasoning is spurious, and would merely serve to confuse readers of English Wikipedia. The article should remain under the common internationally-used name, with redirects from Akko, Akka and anywhere else some readers may look. RolandR 22:41, 17 March 2007 (UTC)
 * (1)RolandR, please refrain from personal attacks.
 * (2)the historical name of Jafo (hebrew sound) is Jaffa (accepted in israel), and the international name for Jerusalem is based on the name it has had since it's creation "yeru-shalem", the conversion between the "yud" and the "J" is standardized. however, Akko, has the historical name of Akka, the name "acre" was a brief name-tag in the sequence of time.. if anything, acre should redirect to akko and not vice-versa. Jaakobou 00:19, 18 March 2007 (UTC)
 * What personal attacks?
 * I repeat, most readers will want to find Acre, not Akko, and that is the name that the article should have. Even the Firefox spell-checker recognises Acre, but not Akko! RolandR 00:44, 18 March 2007 (UTC)
 * Acre is a plot of land, to be expected in a spell checker :) -- Stbalbach 12:57, 18 March 2007 (UTC)
 * 1) Very Strongly Oppose We are here to communicate with English-speaking readers; there is a Hebrew wikipedia for those who speak it. Using "official names" when English usage usage is clear is a violation of Wikipedia policy. "Acre" is not a "survival from the Mandate"; it is common English usage, both older and more recent than the British Mandate. Septentrionalis PMAnderson 23:37, 20 March 2007 (UTC)
 * English speakers also use Akko. Akko is recognized internationally on web sites such as the US Dept of State and United Nations and in many published books in English, there does not appear to be any controversy or lack of recognition of the name Akko by English speakers. Acre may be more commonly known/used because most English speakers discuss or know it in a historical context. It is appropriate to refer to it as Acre when used in a historical context, but this article is not just about the historical city (like Constantinople for example), it is like Leningrad which points to the more modern name of St. Petersburg. -- Stbalbach 01:56, 21 March 2007 (UTC)
 * This is disingenuous. I can only assume Stbalbach has not bothered to make comparisons; in all three cases, the same sources use Acre more frequently.
 * Stbalbach finds two isolated pages at the State Dept. using Akko; the top three results for Acre and Israel all refer to the city ; there may well be more.
 * For the UN, four of the first five.
 * For google.books, all the first page.
 * Furthermore, the Library of Congress country study on Israel, whose usage is recommended by WP:NCGN, uses Acre for the city, both historic and in the most recent Israeli census; it indentifies Akko, rightly, as the Hebrew translation. The Hebrew Wikipedia should, and doubtless does, use it; the English should not. Septentrionalis PMAnderson 21:54, 21 March 2007 (UTC)
 * This is disingenuous. No need for personal attacks. I said in my comment above that these sites make mention of both Acre and Akko. Your implication was only Hebrew speakers use Akko, which is not accurate. Please recognize that English speakers use both Akko and Acre. The "quantity" of name hits on Google is not relevant, the official state name of the city is Akko, just like Leningrad is now called [St. Petersburg]], you can still find people who call it Leningrad (and Constantinope/Instanbul, they even made a song about it). -- Stbalbach 00:44, 22 March 2007 (UTC)
 * This resembles,rather, the recurrent efforts to rename the relevant articles Firenze, İstanbul and Moskva, instead of the English Florence, Istanbul and Moscow; in all these cases, the local spelling is not unknown in English, but it is not common usage. Our policy remains to use the name customary in English: in this case Acre. The nominator appears to be a local booster, unaware of how we do things; but Stbalbach has no such excuse. I will write an RfC if anyone will cosign one. Septentrionalis PMAnderson 13:02, 22 March 2007 (UTC)
 * The three examples you gave are just translations differences, they mean the same thing in both languages, Moskva is the same name as Moscow. In the case of Acre and Akko, they are entirely different names. It is not a translation difference. I think this is where the confusion is: Acre/Akko is like Instanbul/Constantinople or Lengingrad/St. Petersburg. They are entirely different names with different origins and different meanings. Also "Stbalbach has no such excuse" and "nominator appears to be a local booster" -- you need to stick to the issue and stop make personal attacks. This is the second request. -- Stbalbach 23:46, 22 March 2007 (UTC)

Discussion

 * Add any additional comments:

a few extra "akko" refrences:

(1) www.akko.org.il/ (2) www.jewishvirtuallibrary.org/jsource/vie/Acco.html (3) www.stateofisrael.com/tourism/akko/

wiki-related: http://wikitravel.org/en/Akko

Jaakobou 00:53, 18 March 2007 (UTC)

 * Comment. Before I vote, can anyone provide a history of the city name, when it was named, when it changed names? I suppose this could have happened multiple times, like Constantinople/Istanbul. Also would it make sense to have two articles, one for the historical city, and one for the modern, like Constantinople and Istanbul? Thanks. -- Stbalbach 01:46, 18 March 2007 (UTC)

 * ancient history:
 * location is on "tel-aphocar", and it's possible that abraham went by it on his trip from syria to schem (nablus). acording to that version of history, his trip is etched on a mosaic in the ancient city. city in mentioned allready (in writings) in the days of the pharoh "tchotmas" (sp?) the third (roughly 1500BC). as "akka" it is mentioned in the letters of "tel-al amarna". akko is mentioned as "akko" in the bible book of "judges" (chapter 1, verse 31) as a place not taken from the cnaanites by the israelis hebrewenglish.

 * in the days of the second great jewish temple (approx. 400BC-170AD):
 * under roman empire occupation, the city became a helenistic city under the name of "ptulmais" (given by the egyptian occupation of the 2nd century BC, a name that stuck until the muslim occupation of the 7th century) and numereous attacks on the galilee and other places were launched from there... in general, since the times of the greek/romans the city was not considered a fully jewish city... after the great roman destructions (ended approx. 170AD), jews returned to the city and a number of known scholars came out of it. (also mentioned in the talmud)

 * arab/muslim occupation+crusades:
 * around 640AD was occupied by arabs who returned the old name akko, egypt ruler rebuilt the port at 780AD, 1104 the crusader "boldwin the first"(sp?) captured the city and made it the main harbor location for the crusaders. in 1187, it was reoccupied by muslims - the famous salach-a-din. the city withheld siege until recaptured by richard lion-heart in 1191, then it became "capital of the state of jerusalem". in 1229, hosptlar knights came but eventually it was occupied by the mamluchians under the egyptian malik-al-ashraf in 1291.

 * you can identify the cities quarters by an illustration map from 1250 here "acre" - drawn during the british mandate at 1944 <- in the map itself, the name is "ptulmiya"... which is probably a mistake evolving from both the 1500BC pharoh having the name ptulmias and also the egyptian king of the 2nd century BC... who captured it from the greeks and renamed it).

 * starting at 1165 important jewish scholars arrive at the city and by the 13th century, the jewish community in akko is considered one of the more important and central jewish communities in the world.

 * the mamluchi muslim occupation brought an end to the jewish community (another forgotten muslim ethnic cleansing in "palestine") and akko lost it's status.

 * ottoman period:
 * occupied by the muslim ottomans at the early days of the 16th century - controlled by a druze leader - phachar a-din (sp?) up to the early days of the 17th century.

 * in 1741, the jewish community was re-established by rabbi haim ben attar.. the location is currently occupied by the muslim mosque of "dahr al-omar" (violent occurances expunged from history)... rabbi moved to jerusalem and "died suddenly" at the age of 47.

 * in the 18th century, the city was "renovated" under the beduin rule of "dahr al omar" who "confiscated" the jewish temple and turned it into a mosque with his name on it. jews were allowed later to pray in the small ally next to the muslim occupied temple... erm.. mosque.

 * in 1750, a friend of dahr was nominated ruler of egypt and that ruler (ali byyi) and the turkish and damascus rule (this is pre-syria) became somewhat antagonist... in 1969 ali was ordered to amass an army and after he had done so the sultan sent messengers to egypt to kill ali who just declared independance of egypt - dahr helped ali by stopping forces sent from damascus towards ali.

 * in 1771 ali sent an egyptian commander to attack damascus - he was successful, but then returned to egypt to kill ali.. ali ran away to akko. russia helped ali and dahr protect akko with the reinforcement of 3000 albanian soldiers and russian ships... in 1773 ali tried a return to egypt but lost the war and was killed.

 * in 1775, after the russian support for akko stopped (the russia-turky war was over) - the turkish army besieged akko. old man dahr left town with all his wives except for the young pretty one. he returned to akko for her.. and according to the notes his horse trippe and he fell.. head decapiteated and given on a platter to the new ruler.

 * achmad al jazar, the turkish occupiers' officer newly in charge of akko and damascus kicked out the french people from the twon in 1780 as a response to napoleons attempt to use the city as a base for creating mutanywithin'/fighting the ottoman rule... the son of al-jazar, suliman rules the city between 1804-1819.. after him it was tulred by pacha(sp?) abdallah who had a jewish advisor (also the advisor of al-jazar) who was later murdered.

 * in the 1830s the city was reoccupied by egyptian muslims... and in 1840 was attacked by british and reoccupied by ottoman muslims.

 * at the start of the british mandate the city was appox. 6500 in populace - a small fraction of them jews. starting at about 1924 jews came back to resettle the city.

 * during the israeli war of independance (1948), approx. 10000 arabs escaped from the old city and it was left with a minority of arabs. as of now the city is culturally mixed in full, jews and arabs... all calling the city "akko", "acco".

 * "tel akko":
 * has many names - called "tel-aphocar" by arabs since they found many pottery on it. "tel richard lion-heart" in praise of the crusader who fought salach-a-din, "tulon" by crusaders" and also "mount napoleon - after the known frenchmen who tried to take it in 1800 from al-jazar.

 * i hope this historical account makes clear my request for the rename to akko.

 * a fairly reliable version recalls The Crusaders calling the city "Saint-Jean d'Acre" ("Acre" for short) since they mistakenly identified it with the Philistine city of Ekron, in southern Israel (Tel Miqne-Ekron).--

 * i think there should be a better account on who is this "saint jean d'acre" to prevent a confusion about the origin of the name acre - in any event, the name of the city is akko.Jaakobou 11:03, 18 March 2007 (UTC)
 * The above discussion is preserved as an archive of the debate. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

World Heritage Site
Since when has Acre been in the 'region of Europe and North America'? (see infobox). Is this PoV pushing? Imc (talk) 14:25, 21 November 2007 (UTC)

 * For UNESCO purposes, Israel is a European country. The alternative would be "Arab States," so you can see why :) <eleland/talkedits> 18:05, 27 May 2008 (UTC)

 * It looks like this hasn't yet been resolved. UNESCO lists Israel under "Europe and North America" Change it? Toropop (talk) 10:43, 23 December 2012 (UTC)

Unsourced statement removed
I have removed the following statement as it has been marked "citation needed" for several months:
 * According to the first census after the British rule over Acre, the province's population was 100,000 inhabitants, most of whom were Shiite Turks, Turkomans, Azeris, Persians, Bosnians, Albanians, and Circassians as well as a small community of Greeks.

If anyone can find a source, feel free to re-add it. —Angr If you've written a quality article... 16:28, 25 December 2007 (UTC)

Acre, Israel
In the city details on the right, there is no mention that Acre is in Israel, although on the page for Tripoli, it is explicitly stated that it's Tripoli, Lybia. This should be corrected. —Preceding unsigned comment added by Toxvaerd (talk • contribs) 09:33, 13 October 2008 (UTC)

sorry not sure how to properly add to this discussion, but if there is a note in the article concerning how many current arab israelis descended from pre-1948 demographics why not a similar note about the jewish population? it would only be fair for a historical article to address the sources and origins of both communities rather than just the one. 213.181.227.100 (talk) 11:29, 14 October 2008 (UTC)josh

Demogrphics
The section I removed is a claim about general Israeli policy, which does not mention the demographics of Acre. In fact, it does not mention Acre at all. How is this relevant to the section and/or article? Canadian Monkey (talk) 19:26, 12 December 2008 (UTC)
 * I completely agree that the paragraph is not relevant to the article, and while it does mention Acre briefly, it definitely constitutes undue weight. Why does a 1990 statistic have to be talked about so in-depth, not to mention with a POV tone, for example by using the phrase 'Palestinian citizens of Israel'? Unless someone can convince me that this meaningless statistic, which might have some place in Education in Israel if and when that article is expanded, is relevant to the demographics of Acre, I don't think it should go into the article. -- Ynhockey (Talk) 20:30, 12 December 2008 (UTC)
 * I've trimmed the section so as to leave only the part relevant to Acre. -- Nudve (talk) 06:05, 13 December 2008 (UTC)

The typhoid fever of 1948
I wonder, what is the point, beside defamation, to bring the allegations that proved to be unfounded in the history of a 3,000 years old city? Did you know that in 1812/1813 at least half the Muslim population of Acre perished due to plague outbreak? (Thomas Phillip: Acre the rise and fall of a Palestinian city page 176). This was a much larger calamity then the typhoid fever of 1948, but considering the long history of the city I do not believe that even that should be mentioned in the article. Taking a anecdote and making it an important part of the history of Acre (about tenth of the history section in the article is dedicated to that) is wrong. Avihu (talk) 08:01, 15 August 2009 (UTC)
 * If you say it wiped out half of the population, then it's certainly notable. These are exactly the kinds of research-based facts that city articles are lacking. I say add it, if you have access to the source. —Ynhockey (Talk) 23:05, 30 August 2009 (UTC)
 * That's not what I said. I said "half the Muslim population". There was a very large Christian minority and a small Jewish minority (yes, there were Jews in Acre before 1948). But you have missed the point completely. Either you write a very detailed history on the city which might include the fact about the plague outbreak and might include the unfounded suspicions about Jews poisoning wells, or you write a short history about it and give the major events (which the article does, sort of, the sentence "Suleiman Pasha, under whose milder rule the town advanced in prosperity till 1831" is totally wrong), but you can not have both. Avihu (talk) 07:54, 5 September 2009 (UTC)
 * If you don't like the current history section that much, work on a rewrite. Nobody said you couldn't. I am personally not interested enough in the history of Acre to contribute content to it, but would like the article to be improved, so if you can do it, please go ahead. —Ynhockey (Talk) 06:17, 6 September 2009 (UTC)
 * Sorry, but I have enough work in the Hebrew Wikipedia (where the article about Acre is much better). If you prefer the current situation with the Incongruous paragraph about the typhoid fever of 1948, so be it. Avihu (talk) 19:30, 15 September 2009 (UTC)

Suleiman Pasha
The article places Suleiman Pasha as the ruler between Jezzar Pasha and the conquer by Ibrahim Pasha of Egypt. The Israeli wiki claims this is Abdalla Pasha, and has a very detailed article on him. . Can anyone explain? Are they the same person? --Muhandes (talk) 07:58, 19 July 2010 (UTC)
 * OK, I'll sort it out. Suleiman Pasha died in 1819 and was replaced by Abdalla Pasha. --Muhandes (talk) 08:06, 19 July 2010 (UTC)

Popular culture?
Is this section needed? (WP:TRIVIA)? Chesdovi (talk) 11:45, 19 October 2010 (UTC)
 * Oh, its gone! Chesdovi (talk) 11:47, 19 October 2010 (UTC)
 * Good work, Chesdovi! The article looks much better now. But I do think the Knights Hall photo was nice, and think it should be restored.--Geewhiz (talk) 12:05, 19 October 2010 (UTC)
 * If you can make it fit in nicely, go ahead! Chesdovi (talk) 12:34, 19 October 2010 (UTC)

"Sharon" references?
There are a lot of citations to "Sharon, 1997" in the article, but really if that's the author of a book I couldn't find it. Anyone can verify or knows what that book is? 89.141.116.9 (talk) 22:37, 12 January 2014 (UTC)

2008 riots
Can someone add further to the statement that "Ethnic tensions erupted in the city on 8 October 2008 after an Arab citizen drove through a predominantly Jewish neighbourhood". Surely rioting did not break out simply because an Arab drove through a predominantly (but therefore not exclusively) Jewish neighbourhood?Royalcourtier (talk) 23:57, 17 May 2016 (UTC)
 * Yes, it did. "Riots have broken out in the mixed city of Acre, reportedly triggered when an Israeli Arab man drove his car during the Yom Kippur religious holiday. ... The Arab man is reported to have said he was simply driving to a property he owned in the eastern part of the city."

Housekeeping
Per and, this edit established the usages of the page as  and British English. Kindly maintain both consistently, pending a new consensus to the contrary. — Llywelyn II   08:22, 23 November 2018 (UTC)

Semi-protected edit request on 1 February 2021
Please add a link to the orphaned page Saint Jawarjius Church and Monastery, an Oriental Orthodox church located in the city of Acre. https://en.wikipedia.org/wiki/Saint_Jawarjius_Church_and_Monastery Sideriver84 (talk) 07:22, 1 February 2021 (UTC)
 * ❌. Page needs significant improvement and may not be notable. ◢  Ganbaruby!   (Say hi!) 08:57, 2 February 2021 (UTC)

Semi-protected edit request on 10 July 2021
The name Acre most likely derives from the Greek 'Akra' meaning "end, point or extremity" which befits the geography of Acre's natural harbour. 110.22.48.169 (talk) 22:53, 10 July 2021 (UTC)
 * Red information icon with gradient background.svg Not done: please provide reliable sources that support the change you want to be made. ScottishFinnishRadish (talk) 01:00, 11 July 2021 (UTC)

British memorial plaque in Acre
Adding this picture to the Acre (Israel) page is recommended. https://he.wikipedia.org/wiki/%D7%A7%D7%95%D7%91%D7%A5:British_Memorial_Plaque_in_Acre_(Israel)-1.jpg 109.66.117.91 (talk) 11:49, 17 March 2022 (UTC)

Semi-protected edit request on 11 September 2023
In this phrase:

thirty-two per cent of the city's population is Arab

Please change to:

32% of the city's population is Arab

One sentence later, there's a comment about the mayor last being elected with 85% of the vote, not eighty-five per cent of the vote; it helps to use the same format consistently. 123.51.107.94 (talk) 02:41, 11 September 2023 (UTC)
 * ✅ Tollens (talk) 03:42, 11 September 2023 (UTC)

Semi-protected edit request on 30 December 2023
I suggest you remove the "and perhaps diphtheria" section from your section under the 1948 Palestine War section, as that is quite literally impossible. Diphtheria cannot be transferred through water, it is an airborne virus.

It should simply then read "...pouring flasks of typhoid bacteria into the aqueduct," RaccoonLover21 (talk) 03:06, 30 December 2023 (UTC)
 * ✅ The source does mention dysentery, so I added that in the place of diphtheria. Perhaps the original editor mixed up the two. Liu1126 (talk) 14:00, 30 December 2023 (UTC)

Sources for future article expansion
These were previously being (mis)applied in the etym section (they don't source the Egyptian text as being "Akka" at all) but the first isn't bad itself and the second is fantastic. Both could be used for extensive citation or additions of points in the history section. — Llywelyn II   17:38, 14 February 2024 (UTC)

could be used to further source some of the name points or to find areas where the current content might need adjustment.

ditto for the early history and trade networks. — Llywelyn II   10:12, 15 February 2024 (UTC)

Semi-protected edit request on 9 June 2024
A.bulushi85 (talk) 21:01, 9 June 2024 (UTC)
 * Red question icon with gradient background.svg Not done: it's not clear what changes you want to be made. Please mention the specific changes in a "change X to Y" format and provide a reliable source if appropriate.	House Blaster  (talk · he/they) 21:30, 9 June 2024 (UTC)

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Talk:Acre, Israel


text:
Mnemonic major system

The major system (also called the phonetic number system, phonetic mnemonic system, or Herigone's mnemonic system) is a mnemonic technique used to help in memorizing numbers.

The system works by converting numbers into consonants, then into words by adding vowels. The system works on the principle that images can be remembered more easily than numbers.

One notable explanation of this system was given in Martin Gardner's book The First Scientific American Book of Mathematical Puzzles and Diversions (just Mathematical Puzzles and Diversions in the UK edition), which has since been republished in The New Martin Gardner Mathematical Library as Hexaflexagons, Probability Paradoxes, and the Tower of Hanoi. In this, Gardner traces the history of the system back to similar systems of Pierre Hérigone and Richard Grey with uses by Lewis Carroll and Gottfried Wilhelm Leibniz.

The system
Each numeral is associated with one or more consonants. (In other words, the link is to the sound, not the letter. For example, the letters C in "cat", "Cynthia", and "cello" each have different values in the system – 7, 0, and 6, respectively.) Vowels, semivowels and the consonant /h/ are ignored. These can be used as "fillers" to make sensible words from the resulting consonant sequences. A standard mapping is:

The groups of similar sounds and the rules for applying the mappings are almost always fixed, but other hooks and mappings can be used as long as the person using the system can remember them and apply them consistently.

Each numeral maps to a set of similar sounds with similar mouth and tongue positions. The link is phonetic, that is to say, it is the consonant sounds that matter, not the spelling. Therefore, a word like action would encode the number 762 (/k/-/ʃ/-/n/), not 712 (k-t-n). Double letters are disregarded when not pronounced separately, e.g. muddy encodes 31 (/m/-/d/), not 311, but midday encodes 311 (/m/-/d/-/d/) while accept encodes 7091 (/k/-/s/-/p/-/t/) since the ds and cs are pronounced separately. x encodes 70 when pronounced as /ks/ or /gz/ (e.g. in fax and exam) and 76 when pronounced /kʃ/ or /gʒ/ (e.g. in anxious or luxury); z encodes 10 when pronounced /ts/ (e.g. in pizza). In ghost (701, /ɡ/-/s/-/t/) and enough (28, /n/-/f/), gh is being encoded by different numerals. Usually, a rhotic accent is assumed, e.g. fear would encode 84 (/f/-/r/) rather than 8 (/f/).

Often the mapping is compact. Hindquarters, for example, translates unambiguously to 2174140 (/n/-/d/-/k/-/r/-/t/-/r/-/z/), which amounts to a twelve-letter word encoded by seven digits in seven letters, and can be easily visualized.

Each numeral maps to a set of similar sounds with similar mouth and tongue positions. For most people it would be easier to remember 3.1415927 (an approximation of the mathematical constant pi) as:
 * meteor (314, /m/-/t/-/r/)
 * tail (15, /t/-/l/)
 * pink (927, /p/-/ŋ/-/k/, and taking /ŋ/ to be 2)

Short term visual memory of imagined scenes allows large numbers of digits to be memorized with ease. Longer-term memory may require the formulation of more object-related mnemonics with greater logical connection, perhaps forming grammatical sentences that apply to the matter rather than just strings of images.

The system can be employed with phone numbers. One would typically make up multiple words, preferably a sentence, or an ordered sequence of images featuring the owner of the number.

The Major System can be combined with a peg system for remembering lists, and is sometimes used also as a method of generating the pegs. It can also be combined with other memory techniques such as rhyming, substitute words, or the method of loci. Repetition and concentration using the ordinary memory is still required.

An advantage of the major system is that it is possible to use a computer to automatically translate the number into a set of words. One can then pick the best of several alternatives. Such programs include "Numzi" "Rememberg" "Fonbee", the freeware "2Know", and the website "pinfruit".

Example words
Some of these example words may belong to more than one word category.

 * Assumes a rhotic accent
 * nanny (verb): to be overprotective towards
 * mum (adjective): silent; not saying a word
 * agape (adjective): with the mouth wide open, as in wonder, surprise, or eagerness
 * fife (noun): a high-pitched transverse flute used commonly in military and marching musical groups
 * viva (verb): to examine orally
 * fob (verb), archaic: to cheat; deceive

History
A different memory system, the method of loci, was taught to schoolchildren for centuries, at least until 1584, "when Puritan reformers declared it unholy for encouraging bizarre and irreverent images." The same objection can be made over the major system, with or without the method of loci. Mental images may be easier to remember if they are insulting, violent, or obscene (see Von Restorff effect).

Pierre Hérigone (1580–1643) devised the earliest version of the major system. The system was further developed by Stanislaus Mink von Wennsshein in the 17th century. It was later elaborated upon by other users. In 1730, Richard Grey set forth a complicated system that used both consonants and vowels to represent the digits. In 1808 Gregor von Feinaigle introduced the improvement of representing the digits by consonants (but reversed the values of 8 and 9 compared to those listed above).

In 1825 Aimé Paris published the first known version of the major system in its modern form.

In 1843, Carl Otto Reventlow (1817–1873) published a mnemonics textbook on a method similar to Paris' and traveled throughout Germany promoting it.

In 1844 Francis Fauvel Gouraud (1808–1847) delivered a series of lectures introducing his mnemonic system which was based on Aimé Paris' version. The lectures drew some of the largest crowds ever assembled to hear lectures of a "scientific" nature up to that time. This series of lectures was later published as Phreno-Mnemotechny or The Art of Memory in 1845 and his system received wide acclaim. According to Gouraud, Richard Grey indicated that a discussion on Hebrew linguistics in William Beveridge's Institutionum chronotogicarum libri duo, una cum totidem arithmetices chronologicæ libellis (London, 1669) inspired him  to create his system of mnemotechniques which later evolved in to the major system.

In the 1880s Marcus Dwight Larrowe, alias Silas Holmes, was teaching memory courses in the United States based on the Major System using a third alias Dr. Antoine Loisette. Because he was charging inordinate sums of money for a system which had obviously existed before, George S. Fellows published "Loisette" exposed (1888) and included all the material of Larrowe's course which he determined not to be under copyright. The incident was notable enough to gain coverage by way of a book review in the journal Science. A well-known student of Loisette's included Mark Twain whose endorsement Loisette used regularly to sell his course. Following the revelation that he had not originated the system, Larrowe self-published his material under the pseudonym Dr. Antoine Loisette in 1895 and 1896 and it was later re-published by Funk & Wagnalls in 1899.

In the late 1800s Christof Ludwig Poehlmann (aka Christopher Louis Pelman), a German who had emigrated to the United States, and William Joseph Ennever created and ran a series of booklets and memory courses using the system which resulted in The Pelman Schools, The Pelman Institute, and were generally known as Pelmanism.

Poehlmann eventually moved back to Germany around 1910 where he continued offering his memory courses and training apparently with a focus on language learning. indicated that he studied under him for a year in 1911. Fürst later practiced criminal law in Frankfort in pre-Hitler Germany before fleeing, as a Jew, to Prague where he taught at Masaryk University until emigrating to New York in 1939. In 1939, Fürst published Use your Head followed by How to Remember (1944), which was later reprinted as The Practical Way to Better Memory, and followed up with a series of 12 booklets entitled ''You Can Remember! A Home Study Course in Memory and Concentration'' (1946) which all extolled the system, which he called the "Basic List" and the "Number System" along with other mnemonic systems. In a 1946 profile in The New Yorker, Bruno indicates that German scholar Conradus Celtes originated the system.

The system described in this article would be re-popularized after 1957 and through the 1980s in several books by Harry Lorayne, a magician and best selling contemporary author on memory. The most popular of the titles featuring the system is The Memory Book: The Classic Guide to Improving Your Memory at Work, at School, and at Play (1974, with Jerry Lucas).

This phonetic system had another resurgence in the 1990s thanks to the late night infomercials of Kevin Trudeau who sold a series of tapes called Mega Memory. He also published a similar book Kevin Trudeau's Mega Memory which used this same system with some slight modifications.

The name "Major System" may refer to Major Bartlomiej Beniowski, who published a version of the system in his book, The Anti-Absurd or Phrenotypic English Pronouncing and Orthographical Dictionary.

There is a reasonable historical possibility that the roots of the Major System are entangled with older systems of shorthand. It is certainly the case that the underlying structure of the Major System has a direct overlap with Gregg shorthand, which was a popular shorthand system in the late 1800s and early 1900s.

Phonetic number memorization systems also occur in other parts of the world, such as the Katapayadi system going back to at least the 7th Century in India.

Practice
Memory feats centered around numbers can be performed by experts who have learned a 'vocabulary' of at least one image for each 1 and 2-digit number, as these can then be combined to form narratives. Learning a vocabulary of 3-digit numbers is harder, because ten times more images need to be learned for each extra digit. Many mnemonists, however, can use a set of over 1000 images.

The combination of images into a narrative is easier to do rapidly than forming a coherent grammatical sentence. This pre-memorisation and practice at forming images reduces the time required to think up a good imaginary object while creating a strong memorable impression of it. The best words for this purpose are usually nouns, especially those for distinctive objects such as those which make strong impressions on a variety of senses (e.g. "Lime" for 53, as its taste, smell, colour, and even texture are distinctive) or which move (e.g. "arrow" for 4). For basic proficiency, a large vocabulary of image words is not really necessary, since when the table above is reliably learned, it is easy to form your own words ad hoc.

Indexing sequences
Mnemonics often center around learning a complete sequence where all objects in that sequence that come before the one you are trying to recall must be recalled first. For instance, using the mnemonic "Richard of York gave battle in vain" to learn the colours of the rainbow; (red, orange, yellow, green, blue, indigo and violet) to remember what colour comes after indigo, one would have to recall the whole sequence. For a short sequence this may be trivial; for longer lists, it can become complicated and error-prone.

A good example would be in recalling the 53rd element of the periodic table. It might be possible for some people to construct and then learn a string of 53 or more items which you have substituted for the elements and then to recall them one by one, counting them off as you go, but it would be a great deal easier and less laborious/tedious to directly associate element 53 with, for example, a lime (a suitable mnemonic for 53) recalling some prior imagining of yours regarding a mishap where lime juice gets into one's eye - "eye" sounding like "I", the symbol for Iodine. This allows for random access directly to the item, without the need for recalling any previous items.

If you were remembering element 54 in the process of recalling the periodic table you could then recall an image for 54, for instance thinking of a friend called "Laura" (54) in the lotus position looking very Zen-like in order to remind yourself that element 54 is Xenon.

This is an example of combining the Major System with the peg system.

Software

 * iOS app to learn and practice the major system
 * Numzi - free web application for converting numbers to words/phrases and vice versa using the Major System. Covers the English language with over 220,000 words.  Numzi also has an iOS app which is a portable Major System number-word converter.
 * 2Know is free Windows software for converting numbers to words (English, German, French).
 * Mnemisis Another free mnemonic program - runs on Linux, Mac OS X, and Windows
 * Memagine iPhone app that uses the system to teach how to recall a list of up to 100 items in any order
 * Major System iPhone app that helps you to create your own list of words and practice it
 * pinfruit.com Web application for the mnemonic major system
 * Major System Trainer Free personalisable web application for learning the digit mappings, and encodings for all 1 and 2 digit words
 * Major System Tool Free web application for converting numbers to words using Derren Brown's encoding.
 * Mnemonic Major System Module A free module for the drupal content management system by rolf vreijdenberger - web based
 * dingn.com Training and recall of 1 digit to 4 digits numbers, vocabulary cards and a deck of shuffled playing cards with personalized favorite word selection for each number.
 * LOC Serendipity A quiz to learn the sound/number correspondences of the Major system by rote. Also available are quizzes to learn the top 100 adjective and noun representations from 00 to 99.

Other

 * Mammoth Memory's system for memorising decimal numbers 0-999
 * Online mnemonic directory for remembering numbers with the major system
 * Memory Improvement and Learning Information
 * MEMORIAD - Official Website of World Memory Olympiad
 * Homepage of World Memory Championships
 * Numzi Peg Words for 0 - 100, with Peg Word Story
 * Andi Bell's system for the decimal numbers 00-99
 * Collection of Mnemonic Devices

title: Mnemonic major system


text:
Nearest neighbour algorithm

The nearest neighbor algorithm was one of the first algorithms used to solve the travelling salesman problem approximately. In that problem, the salesman starts at a random city and repeatedly visits the nearest city until all have been visited. The algorithm quickly yields a short tour, but usually not the optimal one.

Algorithm
These are the steps of the algorithm:
 * 1) Initialize all vertices as unvisited.
 * 2) Select an arbitrary vertex, set it as the current vertex u. Mark u as visited.
 * 3) Find out the shortest edge connecting the current vertex u and an unvisited vertex v.
 * 4) Set v as the current vertex u. Mark v as visited.
 * 5) If all the vertices in the domain are visited, then terminate. Else, go to step 3.

The sequence of the visited vertices is the output of the algorithm.

The nearest neighbour algorithm is easy to implement and executes quickly, but it can sometimes miss shorter routes which are easily noticed with human insight, due to its "greedy" nature. As a general guide, if the last few stages of the tour are comparable in length to the first stages, then the tour is reasonable; if they are much greater, then it is likely that much better tours exist. Another check is to use an algorithm such as the lower bound algorithm to estimate if this tour is good enough.

In the worst case, the algorithm results in a tour that is much longer than the optimal tour. To be precise, for every constant r there is an instance of the traveling salesman problem such that the length of the tour computed by the nearest neighbour algorithm is greater than r times the length of the optimal tour. Moreover, for each number of cities there is an assignment of distances between the cities for which the nearest neighbor heuristic produces the unique worst possible tour. (If the algorithm is applied on every vertex as the starting vertex, the best path found will be better than at least N/2-1 other tours, where N is the number of vertices.)

The nearest neighbour algorithm may not find a feasible tour at all, even when one exists.

title: Nearest neighbour algorithm


text:
Signal generator

A signal generator is one of a class of electronic devices that generates electrical signals with set properties of amplitude, frequency, and wave shape. These generated signals are used as a stimulus for electronic measurements, typically used in designing, testing, troubleshooting, and repairing electronic or electroacoustic devices, though it often has artistic uses as well.

There are many different types of signal generators with different purposes and applications and at varying levels of expense. These types include function generators, RF and microwave signal generators, pitch generators, arbitrary waveform generators, digital pattern generators, and frequency generators. In general, no device is suitable for all possible applications.

A signal generator may be as simple as an oscillator with calibrated frequency and amplitude. More general-purpose signal generators allow control of all the characteristics of a signal. Modern general-purpose signal generators will have a microprocessor control and may also permit control from a personal computer. Signal generators may be free-standing self-contained instruments, or may be incorporated into more complex automatic test systems.

History
In June 1928, the General Radio 403 was the first commercial signal generator ever marketed. It supported a frequency range of 500 Hz to 1.5 MHz. Also, in April 1929, the first commercial frequency standard was marketed by General Radio with a frequency of 50 KHz.

Function generator

A function generator is a device which produces simple repetitive waveforms. Such devices contain an electronic oscillator, a circuit that is capable of creating a repetitive waveform. (Modern devices may use digital signal processing to synthesize waveforms, followed by a digital-to-analog converter, or DAC, to produce an analog output.) The most common waveform is a sine wave, but sawtooth, step (pulse), square, and triangular waveform oscillators are commonly available as are arbitrary waveform generators (AWGs). If the oscillator operates above the human hearing range (>20 kHz), the generator will often include some sort of modulation function such as amplitude modulation (AM), frequency modulation (FM), or phase modulation (PM) as well as a second oscillator that provides an audio frequency modulation waveform.

Arbitrary waveform generator
An arbitrary waveform generator (AWG or ARB) is a sophisticated signal generator that generates arbitrary waveforms within published limits of frequency range, accuracy, and output level. Unlike a function generator that produces a small set of specific waveforms, an AWG allows the user to specify a source waveform in a variety of different ways. An AWG is generally more expensive than a function generator and often has less bandwidth. An AWG is used in higher-end design and test applications.

RF and microwave signal generators
RF (radio frequency) and microwave signal generators are used for testing components, receivers and test systems in a wide variety of applications including cellular communications, WiFi, WiMAX, GPS, audio and video broadcasting, satellite communications, radar and electronic warfare. RF and microwave signal generators normally have similar features and capabilities, but are differentiated by frequency range. RF signal generators typically range from a few kHz to 6 GHz, while microwave signal generators cover a much wider frequency range, from less than 1 MHz to at least 20 GHz. Some models go as high as 70 GHz with a direct coaxial output, and up to hundreds of GHz when used with external waveguide multiplier modules. RF and microwave signal generators can be classified further as analog or vector signal generators.

Analog signal generators
Analog signal generators based on a sine-wave oscillator were common before the inception of digital electronics, and are still used. There was a sharp distinction in purpose and design of radio-frequency and audio-frequency signal generators.

RF signal generators produce continuous wave radio frequency signals of defined, adjustable, amplitude and frequency. Many models offer various types of analog modulation, either as standard equipment or as an optional capability to the base unit. This could include AM, FM, ΦM (phase modulation) and pulse modulation. A common feature is an attenuator to vary the signal’s output power. Depending on the manufacturer and model, output powers can range from −135 to +30 dBm. A wide range of output power is desirable, since different applications require different amounts of signal power. For example, if a signal has to travel through a very long cable out to an antenna, a high output signal may be needed to overcome the losses through the cable and still have sufficient power at the antenna. But when testing receiver sensitivity, a low signal level is required to see how the receiver behaves under low signal-to-noise conditions.
 * RF

RF signal generators are available as benchtop instruments, rackmount instruments, embeddable modules and in card-level formats. Mobile, field-testing and airborne applications benefit from lighter, battery-operated platforms. In automated and production testing, web-browser access, which allows multi-source control, and faster frequency switching speeds improve test times and throughput.

RF signal generators are required for servicing and setting up radio receivers, and are used for professional RF applications.

RF signal generators are characterized by their frequency bands, power capabilities (−100 to +25 dBc), single side band phase noise at various carrier frequencies, spurs and harmonics, frequency and amplitude switching speeds and modulation capabilities.

Audio-frequency signal generators generate signals in the audio-frequency range and above. An early example was the HP200A audio oscillator, the first product sold by the Hewlett-Packard Company in 1939. Applications include checking frequency response of audio equipment, and many uses in the electronic laboratory.
 * AF

Equipment distortion can be measured using a very-low-distortion audio generator as the signal source, with appropriate equipment to measure output distortion harmonic-by-harmonic with a wave analyser, or simply total harmonic distortion. A distortion of 0.0001% can be achieved by an audio signal generator with a relatively simple circuit.

Vector signal generator
With the advent of digital communications systems, it is no longer possible to adequately test these systems with traditional analog signal generators. This has led to the development of the vector signal generator, which is also known as a digital signal generator. These signal generators are capable of generating digitally-modulated radio signals that may use any of a large number of digital modulation formats such as QAM, QPSK, FSK, BPSK, and OFDM. In addition, since modern commercial digital communication systems are almost all based on well-defined industry standards, many vector signal generators can generate signals based on these standards. Examples include GSM, W-CDMA (UMTS), CDMA2000, LTE, Wi-Fi (IEEE 802.11), and WiMAX (IEEE 802.16). In contrast, military communication systems such as JTRS, which place a great deal of importance on robustness and information security, typically use very proprietary methods. To test these types of communication systems, users will often create their own custom waveforms and download them into the vector signal generator to create the desired test signal.

Digital pattern generator
A logic signal generator or data pattern generator or digital pattern generator produces logic signals—that is, logical 1s and 0s in the form of conventional voltage levels. The usual voltage standards are LVTTL and LVCMOS. It is different from a "pulse/pattern generator", which refers to signal generators able to generate logic pulses with different analog characteristics (such as pulse rise/fall time, high level length, ...).

A digital pattern generator is used as stimulus source for digital integrated circuits and embedded systems - for functional validation and testing.

Special purpose signal generators

In addition to the above general-purpose devices, there are several classes of signal generators designed for specific applications.

Pitch generators and audio generators
A pitch generator is a type of signal generator optimized for use in audio and acoustics applications. Pitch generators typically include sine waves over the human hearing range (20 Hz to 20 kHz). Sophisticated pitch generators will also include sweep generators (a function which varies the output frequency over a range, in order to make frequency-domain measurements), multipitch generators (which output several pitches simultaneously, and are used to check for intermodulation distortion and other non-linear effects), and tone bursts (used to measure response to transients). Pitch generators are typically used in conjunction with sound level meters, when measuring the acoustics of a room or a sound reproduction system, and/or with oscilloscopes or specialized audio analyzers.

Many pitch generators operate in the digital domain, producing output in various digital audio formats such as AES3, or SPDIF. Such generators may include special signals to stimulate various digital effects and problems, such as clipping, jitter, bit errors; they also often provide ways to manipulate the metadata associated with digital audio formats.

The term synthesizer is used for a device that generates audio signals for music, or that uses slightly more intricate methods.

Computer programs
Computer programs can be used to generate arbitrary waveforms on a general-purpose computer and output the waveform via an output interface. Such programs may be provided commercially or be freeware. Simple systems use a standard computer sound card as output device, limiting the accuracy of the output waveform and limiting frequency to lie within the audio-frequency band.

Video signal generator
A video signal generator is a device which outputs predetermined video and/or television waveforms, and other signals used to stimulate faults in, or aid in parametric measurements of, television and video systems. There are several different types of video signal generators in widespread use. Regardless of the specific type, the output of a video generator will generally contain synchronization signals appropriate for television, including horizontal and vertical sync pulses (in analog) or sync words (in digital). Generators of composite video signals (such as NTSC and PAL) will also include a colorburst signal as part of the output. Video signal generators are available for a wide variety of applications and for a wide variety of digital formats; many of these also include audio generation capability (as the audio track is an important part of any video or television program or motion picture).

title: Signal generator