Digital Audio Tape
Digital Audio Tape (DAT or R-DAT) is a signal recording and playback medium developed by Sony in the mid 1980s. 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 the name suggests, the recording is digital rather than analog. DAT has the ability to record at higher, equal or lower sampling rates than a CD (48, 44.1 or 32 kHz sampling rate respectively) at 16 bits quantization. If a digital source is copied then the DAT will produce an exact clone, unlike other digital media such as Digital Compact Cassette or non-Hi-MD MiniDisc, both of which use lossy data compression.
Like most formats of videocassette, a DAT cassette may only be recorded on one side, unlike an analog compact audio cassette.
Development
The technology of DAT is closely based on that of video recorders, using a rotating head and helical scan to record data. This prevents DATs from being physically edited in the cut-and-splice manner of analog tapes, or open-reel digital tapes like ProDigi or DASH.
The DAT standard allows for four sampling modes: 32 kHz at 12 bits, and 32 kHz, 44.1 kHz or 48 kHz at 16 bits. Certain recorders operate outside the specification, allowing recording at 96 kHz and 24 bits (HHS). Some machines aimed at the domestic market did not operate at 44.1 kHz when recording from analog sources. Since each recording standard uses the same tape, the quality of the sampling has a direct relation to the duration of the recording – 32 kHz at 12 bits will allow six hours of recording onto a three hour tape while HHS will only give 90 minutes from a three hour tape. Included in the signal data are subcodes to indicate the start and end of tracks or to skip a section entirely; this allows for indexing and fast seeking. Two-channel stereo recording is supported under all sampling rates and bit depths, but the R-DAT standard does support 4-channel recording at 32 kHz.
DAT "tapes" are between 15 and 180 minutes in length, a 120-minute tape being 60 meters in length. DAT "tapes" longer than 60 meters tend to be problematic in DAT recorders due to the thinner media.
Predecessor formats
DAT was not the first digital audio tape; pulse-code modulation (PCM) was used in Japan to produce analogue phonograph records in the early 1970s, using a videotape recorder for its transport, but this was not developed into a consumer product.
Later in 1976, the first commercially successful digital audio tape format was developed by Soundstream, using 1" (2.54 cm) wide reel-to-reel tape loaded on an instrumentation recorder manufactured by Honeywell acting as a transport, which in turn was connected to outboard digital audio encoding and decoding hardware of Soundstream's own design. Several major record labels like RCA and Telarc used Soundstream's system to record some of the first commercially-released digital audio recordings.
Soon after Soundstream, 3M starting in 1978 introduced their own line (and format) of digital audio tape recorders for use in a recording studio, with one of the first prototypes being installed in the studios of Sound 80 in Minneapolis, Minnesota.
Professional systems using a PCM adaptor, 98'7789 /'which digitized an analog audio signal and then encoded this resulting digital stream into an analog video signal so that a conventional VCR could be used as a storage medium, were also common as mastering formats starting in the late 1970s.
dbx, Inc.'s Model 700 system, notable for using high sample-rate delta-sigma modulation (similar to modern Super Audio CDs) rather than PCM, and Decca's PCM system in the 1970s (using a videotape recorder manufactured by IVC for a transport), are two more examples.
Mitsubishi's X-80 digital recorder was another 6.4 mm (¼") open reel digital mastering format that used a very unusual sampling rate of 50.4 kHz.
For high-quality studio recording, effectively all of these formats were made obsolete in the early 1980s by two competing reel-to-reel formats with stationary heads: Sony's DASH format and Mitsubishi's continuation of the X-80 recorder, which was improved upon to become the ProDigi format. (In fact, the first ProDigi-format recorder, the Mitsubishi X-86, was playback-compatible with tapes recorded on an X-80.) Both of these formats remained popular as an analog alternative until the early 1990s, when hard disk recorders rendered them obsolete.
R-DAT and S-DAT
For a while, the DAT format was produced in two physically incompatible formats: one with helical scaning heads, called R-DAT, and one with a stationary head block, called S-DAT. S-DAT failed to gain market share as it required more expensive technlogy in the machine, compared to the relatively simple (and much cheaper) spinning head approach of R-DAT.
Philips later recycled the basic mechanical design of S-DAT into DCC.