Digital Audio Tape

Digital Audio Tape (DAT or R-DAT) is a discontinued digital recording and playback medium developed by Sony and introduced in 1987. In appearance it is similar to a Compact Cassette, using 3.81 mm / 0.15" (commonly referred to as 4 mm) magnetic tape enclosed in a protective shell, but is roughly half the size at 73 mm × 54 mm × 10.5 mm. The recording is digital rather than analog. DAT can record at sampling rates equal to, as well as higher and lower than a CD (44.1, 48, or 32 kHz sampling rate respectively) at 16 bits quantization. If a comparable digital source is copied without returning to the analogue domain, 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 a lossy data-reduction system.

Similar to most formats of videocassette, a DAT cassette may only be recorded and played in one direction, unlike an analog compact audio cassette. Many DAT recorders had the capability to embed program numbers and IDs into the recording which can be used to select an individual track like on a CD player.

Although intended as a replacement for analog audio compact cassettes, the format was never widely adopted by consumers because of its expense, as well as concerns from the music industry about unauthorized high-quality copies. The format saw moderate success in professional markets and as a computer storage medium, which was developed into the Digital Data Storage format. Sony ceased production of new recorders making it more difficult to play archived recordings in this format. Magnetic tape degradation has been noted by some engineers involved in re-mastering archival recordings on DAT, which presents a threat to audio held exclusively in this medium.

The basic tape mechanism of DAT is closely based on 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. In 1983, a DAT meeting was established to unify the standards for recording digital audio on magnetic tape developed by each company and in 1985, two standards were created: R-DAT (Rotating Digital Audio Tape) using a rotary head and S-DAT (Stationary Digital Audio Tape) using a fixed head. The S-DAT format had a simple mechanism similar to the Compact Cassette format but was difficult to develop a fixed recording head for high-density recording while the rotating head of the R-DAT had a proven track record in VCR formats like VHS & Betamax. As the S-DAT version was never released, R-DAT had been renamed as simply "DAT" by the time of its launch. However, Philips and Matsushita (Panasonic) would later release their own stationary head digital format in the form of the Digital Compact Cassette. Sony would later introduce another rotating head format in the form of NT which was intended to replace the Microcassette and Mini-Cassette.^{[citation needed]}

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 early machines aimed at the consumer market did not operate at 44.1 kHz when recording so they could not be used to 'clone' a compact disc. 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 the same 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.^{[citation needed]}

DATs are between 15 and 180 minutes in length, a 120-minute tape being 60 metres in length. DATs longer than 60 metres tend to be problematic in DAT recorders due to the thinner media. DAT machines running at 48 kHz and 44.1 kHz sample rates transport the tape at 8.15 mm/s. DAT machines running at 32 kHz sample rate transport the tape at 4.075 mm/s.^{[citation needed]}

DAT was not the first digital audio tape; pulse-code modulation (PCM) was used in Japan by Denon in 1972 for the mastering and production of analogue phonograph records, using a 2-inch Quadruplex-format videotape recorder for its transport, but this was not developed into a consumer product. Denon's development dated from its work with Japan's NHK Broadcasting; NHK developed the first high-fidelity PCM audio recorder in the late 1960s. Denon continued development of their PCM recorders that used professional video machines as the storage medium, eventually building 8-track units used for, among other productions, a series of jazz records made in New York in the late 1970s.^{[citation needed]}

In 1976, another digital audio tape format was developed by Soundstream, using one inch (25.4 mm) 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. Soundstream's format was improved through several prototypes and when it was developed to 50 kHz sampling rate at 16 bits, it was deemed good enough for professional classical recording by the company's first client, Telarc Records of Cleveland, Ohio. Telarc's April, 1978 recording of the Holst Suites for Band by Frederick Fennell and the Cleveland Wind Ensemble was a landmark release, and ushered in digital recording for America's classical music labels. Soundstream's system was also used by RCA.^{[citation needed]}