PCM adaptor
A PCM adaptor is a device used for recording digital audio
Digital audio
Digital audio is sound reproduction using pulse-code modulation and digital signals. Digital audio systems include analog-to-digital conversion , digital-to-analog conversion , digital storage, processing and transmission components...

 in the PCM
Pulse-code modulation
Pulse-code modulation is a method used to digitally represent sampled analog signals. It is the standard form for digital audio in computers and various Blu-ray, Compact Disc and DVD formats, as well as other uses such as digital telephone systems...

 format, which in turn connects to a video cassette recorder (acting as a transport
Transport (recording)
A transport is a device that handles a particular physical storage medium itself, and extracts or records the information to and from the medium, to an outboard set of processing electronics that the transport is connected to.A transport houses no electronics itself for encoding and decoding the...

) for storage and playback of the digital audio information.

How a PCM adaptor works

High-quality PCM audio requires a significantly larger bandwidth than a regular FM
Frequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...

-modulated analog audio signal. For example, a 16-bit PCM signal requires an analog bandwidth of about 1-1.5 MHz (compared to about 15-20 kHz of analog bandwidth required for an analog audio signal), and, clearly, a standard analog audio recorder could not meet that requirement. One solution arrived at in the early 1980s, was to use a video tape recorder, which is capable of recording signals with this high bandwidth, to store the audio information, but a means of converting the digital audio into pseudo-video was necessary. Such an audio recording system therefore includes two devices, namely the PCM adaptor, which converts audio into pseudo-video, and the video tape recorder itself. A PCM adaptor has the analogue audio (stereo) signal as its input, and translates it into a series of binary digits, which, in turn, is coded and modulated into a monochrome (black and white) video signal, appearing as a vibrating checkerboard pattern, modulated with the audio, which can then be recorded as a video signal.

This video signal can be stored on any ordinary analog video tape recorder, since these were the only widely available devices with sufficient bandwidth. This helps to explain the choice of sampling frequency for the CD, because the number of video lines, frame rate and bits per line end up dictating the sampling frequency one can achieve. The sampling frequency of 44.1 kHz was also adopted in the Compact Disc
Compact Disc
The Compact Disc is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage , write-once audio and data storage , rewritable media , Video Compact Discs , Super Video Compact Discs ,...

, as at that time, there was no other practical way of storing digital sound than by a PCM Converter & video recorder combination. The sampling frequencies of 44.1 and 44.056 kHz were thus the result of a need for compatibility with the 25-frame (PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...

 countries) and 30-frame black and white (NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...

 countries) video formats used for audio storage at the time. (Note that neither PAL nor NTSC was itself used, the black and white version of video storage was used with no color subcarrier.)

Most video-based PCM adaptors record audio at 16 bits quantization, and a sampling frequency of 44.1 for NTSC countries (or 44.056 for PAL countries) kHz. However, some of the earlier models, such as the Sony PCM-100, recorded 16-bits quantization as well, but used only 14 of the bits for the audio, with the remaining 2 bits used for error correction, in case of dropout
Dropout (electronics)
Dropout within the realm of electronics and electrical engineering, has a number of uses.It is the dropping away of a flake of magnetic material from magnetic tape, leading to loss of signal, or a failure to properly read a binary character from data storage...

s or other anomalies being present on the videotape.

A PCM adaptor can only store a single stereo signal, and is not capable of studio multi-track recording.

Models of PCM adaptors

The Sony PCM-1600 was the first commercial video-based 16-bit recorder (using a special U-matic
U-matic is an analog recording videocassette format first shown by Sony in prototype in October 1969, and introduced to the market in September 1971. It was among the first video formats to contain the videotape inside a cassette, as opposed to the various Reel-to-Reel or open-reel formats of the...

 VCR for a transport), and continues in its 1610 and 1630 incarnations. The 1600 was one of the first systems used for mastering audio compact disc
Compact Disc
The Compact Disc is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage , write-once audio and data storage , rewritable media , Video Compact Discs , Super Video Compact Discs ,...

s in the early 1980s by many major record labels.

Several semi-professional/consumer models of PCM adaptor were also released by Sony, including:
  • Sony Digital Audio Processor PCM-F10 (the first consumer-marketed model),
  • Sony Digital Audio Processor PCM-F1 (which was sold with a companion Betamax
    Betamax was a consumer-level analog videocassette magnetic tape recording format developed by Sony, released on May 10, 1975. The cassettes contain -wide videotape in a design similar to the earlier, professional wide, U-matic format...

    -format VCR, the Sony SL-2000 or SL-F1, for recording & playback).
  • Sony Digital Audio Processor PCM-100,
  • SONY Digital Audio Processor PCM-501ES
    SONY Digital Audio Processor PCM-501ES
    The Sony PCM-501ES digital audio processor is a piece of equipment that offers digital sound recording and playback. It was released in 1984 and was sold as a semi-professional product, part of the PCM adaptor family of products. The cost was about 900 USD. It was by far the most popular of all the...

  • Sony Digital Audio Processor PCM-601,
  • Sony Digital Audio Processor PCM-701.

Technics may refer to:* Technics turntables, no longer in production.* Technics , a brand name of the Panasonic Corporation* An anglicization of the Ancient Greek term techne, used primarily in media theory...

 also made a portable PCM adaptor as well, the SV-100, and a version with a built-in VHS
The Video Home System is a consumer-level analog recording videocassette standard developed by Victor Company of Japan ....

 videocassette transport, the SV-P100. Nakamichi
is an historic Japanese high end audio company most famous for its innovative and very high quality audio cassette decks.In 1972, Nakamichi launched its first Nakamichi-brand products, home audio gear that included the world's first three-head cassette deck...

 as well manufactured a PCM adaptor, the DMP-100.

dbx, Inc.
Dbx, Inc.
dbx, Inc. is an American producer of professional audio recording equipment. It was founded by David E. Blackmer in 1971. The original company goal was: "To get closer to the realism of a live performance." Its early products were based on the concept of using decibel expansion which gave the...

 also manufactured a PCM adaptor, the Model 700
Dbx Model 700 Digital Audio Processor
The dbx Model 700 Digital Audio Processor was a professional audio ADC/DAC combination unit, which digitized a stereo analog audio input into a bitstream, which was then encoded and encapsulated in an analog composite video signal, for recording to tape using a VCR as a transport...

. It differed from the above listed models in the fact that it did not use PCM, but rather delta-sigma modulation
Delta-sigma modulation
Delta-sigma modulation is a method for encoding high-resolution or analog signals into lower-resolution digital signals. The conversion is done using error feedback, where the difference between the two signals is measured and used to improve the conversion...

. This resulted in a higher quality digital recording with more dynamic range
Dynamic range
Dynamic range, abbreviated DR or DNR, is the ratio between the largest and smallest possible values of a changeable quantity, such as in sound and light. It is measured as a ratio, or as a base-10 or base-2 logarithmic value.-Dynamic range and human perception:The human senses of sight and...

 than what standard PCM modulation could offer. Like a standard PCM adaptor, the Model 700 also utilized a VCR for a transport.

The obsolescence of the PCM adaptor

A few years after the PCM adaptor's introduction, Sony introduced in 1987 a new cassette-based format for digital audio recording called DAT
Digital Audio Tape
Digital Audio Tape is a signal recording and playback medium developed by Sony and introduced in 1987. In appearance it is similar to a compact audio cassette, using 4 mm magnetic tape enclosed in a protective shell, but is roughly half the size at 73 mm × 54 mm × 10.5 mm. As...

 (Digital Audio Tape). DAT was a much more portable and less-cumbersome format to use than a PCM adaptor-based system, since DAT no longer relied on a separate video cassette recorder. Instead, DAT recorders had their own built-in transport using a small cassette unique to the format. DAT used tape 4 millimeters ( .157 inches) in width loaded into a cassette 73 mm × 54 mm × 10.5 mm (2.87 in. x 2.12 in. x 0.41 in.) in size. The audio data was recorded to the tape in the same fashion that a VCR connected to a PCM adaptor would record to a videotape, by using helical scan
Helical scan
Helical scan is a method of recording high bandwidth signals onto magnetic tape. It is used in reel-to-reel video tape recorders, video cassette recorders, digital audio tape recorders, and some computer tape drives....

 recording. In essence, DAT was a modernized, integrated, and miniaturized version of a PCM adaptor-based system.

DAT could only record 2 tracks of audio for stereo at a time, much like a PCM adaptor, but the smaller size of the equipment and media, as well as being able to accept multiple sampling rates (the standard 44.1 kHz, as well as 48 kHz, and 32 kHz, all at 16 bits per sample, and a special "LP" recording mode using 12 bits per sample at 32 kHz for extended recording time) gave DAT many advantages over PCM adaptor-based systems.

Digital recorders capable of multi-track recording (as opposed to only two tracks for stereo that a PCM adaptor or DAT could record) such as Mitsubishi
The Mitsubishi Group , Mitsubishi Group of Companies, or Mitsubishi Companies is a Japanese multinational conglomerate company that consists of a range of autonomous businesses which share the Mitsubishi brand, trademark and legacy...

's ProDigi
Mitsubishi's ProDigi is a professional audio, reel-to-reel, digital audio tape format with a stationary head position, similar to Sony's Digital Audio Stationary Head, which competed against ProDigi when the format was available in the mid 1980s through the early 1990s...

 format and Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....

Digital Audio Stationary Head
The Digital Audio Stationary Head or DASH standard is a reel-to-reel, digital audio tape format introduced by Sony in early 1982 for high-quality multitrack studio recording and mastering, as an alternative to analog recording methods. DASH is capable of recording two channels of audio on a...

 format also became available on the professional audio market about the same time as the introduction of PCM encoder/decoders made for use with video tape recorders. Machines for these formats had their own transports built-in as well, using reel-to-reel tape in either 1/4", 1/2", or 1" widths, with the audio data being recorded to the tape using a multi-track stationary tape head. ADAT
Alesis Digital Audio Tape or ADAT is a magnetic tape format used for the simultaneous digital recording of eight analog audio or digital audio tracks at once, onto a Super VHS tape that is used by consumer VCRs.- History :...

also became available in the early 1990s, which allowed eight-track 44.1 or 48 kHz recording on S-VHS cassettes.

Formats like ProDigi and DASH were referred to as SDAT (Stationary-head Digital Audio Tape) formats, as opposed to formats like the PCM adaptor-based systems and DAT, which were referred to as RDAT (Rotating-head Digital Audio Tape) formats, due to their helical-scan process of recording.

Like the DAT cassette, ProDigi and DASH machines also accommodated the obligatory 44.1 kHz sampling rate, but also 48 kHz on all machines, and a 96 kHz sampling rate on the last-generation units. They overcame the problems that made typical analog recorders unable to meet the bandwidth (frequency range) demands of digital recording by a combination of higher tape speeds, narrower head gaps used in combination with metal-formulation tapes, and the spreading of data across multiple parallel tracks.
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