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Digital Audio Tape

Abbreviation for Digital Audio Tape. DAT is a signal recording and playback medium introduced by Sony in 1987. It is similar in appearance to a compact audio cassette, using 1/8″ magnetic tape enclosed in a protective shell, but is roughly half the size. DAT tapes are between 15 and 180 minutes in length. As the name suggests, the recording is digital rather than analog, DAT converting and recording is done without data compression, which means that the entire input signal is retained. If a digital source is copied then the DAT will produce an exact clone, unlike other digital media such as Digital Compact Cassette or MiniDisc, both of which use lossy data compression.

There were originally two different formats of DAT: S-DAT and R-DAT. S-DAT refers to machines with a stationary record/play head, while R-DAT refers to the rotating head variety. S-DAT technology never gained wide acceptance and pretty much faded into obscurity (though there are some specialized variants in use today). The “R” distinction of R-DAT became unnecessary and soon it was just known as DAT. The technology of R-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, as DASH (a stationary head digital tape format that was pretty common in its day), or analog tape recordings can be.

The DAT standard allows for four sampling modes: 32kHz at 12 bits, and 32kHz, 44.1kHz or 48 kHz at 16 bits. Certain recorders operate outside the specification, allowing recording at 96 kHz and 24 bits (HHS). 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, which allows for indexing and fast seeking. The tapes themselves are not physically editable, in the cut-and-splice manner of analog tapes. 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.

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