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). 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 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's ProDigi format and Sony's DASH 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 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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