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As the name suggests the recording is digital rather than analog, DAT converting and recording at higher, equal or lower sampling rates than a CD (48, 44.1 or 32 kHz sampling rate, and 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.
History
DevelopmentThe 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 formatsDAT 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.
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