|MadSci Network: Computer Science|
OneOff Media http://www.oneoffcd.com/info/historycd.cfm says that the decision was an agreement between Sony and Philips, with this timeline: 1969 Sony introduces it's 13-bit PCM digital recorder at a 47.25 kHz (47,250 time per second) sampling rate. The digital recording is sent to a 2" video tape. Klass Compaan, a Dutch physicist comes up with the idea for the Compact Disc. 1970 At Philips, Compaan and Pete Kramer complete a glass disc prototype and determine that a laser will be needed to read the information. 1978 Philips releases the video disc player Sony sells the PCM-1600 and PCM-1 (digital audio processors) "Digital Audio Disc Convention" Held in Tokyo, Japan with 35 different manufacturers. Philips proposes that a worldwide standard be set. 1979 Prototype CD System demonstrated in Europe and Japan. Sony agrees to join in collaboration. Sony & Philips compromise on the standard sampling rate of a CD -- 44.1 kHz (44,100 samples per second) 1980 Compact Disc standard proposed by Philips & Sony. 1981 Matsushita accepts Compact Disc Standard Digital Audio Disc Committee also accepts Compact Disc Standard. ============= According to this website from Columbia University http://www.cs.columbia.edu/~hgs/audio/44.1.html, the decision was logical giving the desire for compatibility with televisions with two standards consistent with 50 Hz and 60 Hz electricity: Explanation of 44.1 kHz CD sampling rate The CD sampling rate has to be larger than about 40 kHz to fulfill the Nyquist criterion that requires sampling at twice the maximum analog frequency, which is about 20 kHz for audio. The sampling frequency is chosen somewhat higher than the Nyquist rate since practical filters neede to prevent aliasing have a finite slope. Digital audio tapes (DATs) use a sampling rate of 48 kHz. It has been claimed that thier sampling rate differs from that of CDs to make digital copying from one to the other more difficult. 48 kHz is, in principle, a better rate since it is a multiple of the other standard sampling rates, namely 8 and 16 kHz for telephone-quality audio. Sampling rate conversion is simplified if rates are integer multiples of each other. From John Watkinson, The Art of Digital Audio, 2nd edition, pg. 104: "Video recorders... were adapted to store audio samples by creating a pseudo-video waveform which would convey binary as black and white levels. The sampling rate of such a system is constrained to relate simply to the field rate and field structure of the television standard used, so that an integer number of samples can be stored on each usable TV line in the field. Such a recording can be made on a monochrome recorder, and these recording are made in two standards, 525 lines at 60 Hz and 625 lines at 50 Hz. Thus it is possible to find a frequency which is a common multiple of the two and is also suitable for use as a sampling rate. The allowable sampling rates in a pseudo-video system can be deduced by multiplying the field rate by the number of active lines in a field (blanking lines cannot be used) and again by the number of samples in a line. By careful choice of parameters it is possible to use either 525/60 or 625/50 video with a sampling rate of 44.1KHz. In 60 Hz video, there are 35 blanked lines, leaving 490 lines per frame or 245 lines per field, so the sampling rate is given by : 60 X 245 X 3 = 44.1 KHz In 50 Hz video, there are 37 lines of blanking, leaving 588 active lines per frame, or 294 per field, so the same sampling rate is given by 50 X 294 X3 = 44.1 Khz. The sampling rate of 44.1 KHz came to be that of the Compact Disc. Even though CD has no video circuitry, the equipment used to make CD masters is video based and determines the sampling rate. ============= According to Wikipedia at http://en.wikipedia.org/wiki/Compact_disc#Origins_of_44.1_kHz_sampling: Origins of 44.1 kHz sampling The highest frequency that a human ear can detect is approximately 20,000 Hz. The compact disc was designed with the capability to contain the full audible range, and thus overcome the limitations of previous consumer-level audio carriers. The provable Nyquist–Shannon sampling theorem states that when quantizing a signal of a given bandwidth (20 kHz in this case, 0 - 20 kHz), in order to be able to reproduce the original waveform perfectly from the digitized information, the sampling rate used in the quantization has to be more than twice the amount of bandwidth. Thus, the sample rate needed to be over 40 kHz. As real-world components do not adhere to the ideal situation behind the theorem, and CD players designed with even lower-class analogue components might not achieve desired results (producing audible distortion), the sampling rate was raised well over the ideal minimum requirement. The exact sampling rate of 44.1 kHz is inherited from a method of converting digital audio into an analog video signal for storage on video tape, which was the most affordable way to store it at the time the CD specification was being developed. A device that turns an analog audio signal into PCM audio, which in turn is changed into an analog video signal is called a PCM adapter. PCM technology could store six samples (three samples per each stereo channel) in a single horizontal line. A standard NTSC video signal has 245 usable lines per field, and 59.94 fields/s, which works out at 44,056 samples/s. Similarly PAL has 294 lines and 50 fields, which gives 44,100 samples/s. * This system could either store 14-bit samples with some error correction, or 16-bit samples with almost no error correction. * There was a long debate over whether to use 14 or 16 bit samples and/or 44,056 or 44,100 samples/s when the Sony/Philips task force designed the compact disc; 16 bits and 44.1 kilo-samples/s prevailed.
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