Digital audio tape
The Digital Audio Tape ( DAT ) is a digital audio - magnetic tape ( tape ) for corresponding audio recorder . The recording format and the sound quality are essentially the same as those of the audio CD and, on some devices, go well beyond this. The first devices appeared in the late 1980s. The technology was intended as the successor to the very widespread audio cassette , but could not establish itself on the mass market. Today it is only important in professional niche applications - for example in recording studios or as a backup medium for computer data .
technology
The information is stored on a magnetic tape . However, quality and convenience are significantly increased compared to analog cassette recorders due to the digital recording. With a sampling rate of up to 96 kHz and a maximum resolution of 24 bits, the sound potential is higher than that of the audio CD; however, this was not available in all devices. Most commonly used was the audio CD equivalent format with 44.1 kHz sampling rate and 16 bit.
The R-DAT recorder (R for rotary head) uses an azimuth recording process like the VHS video process, which is similar in its basic structure . Both heads are inclined by 20 °. The tape of the R-DAT is a data-tight metal powder bandage. In addition to the audio signal, subcodes are recorded on it, which can contain manufacturer-specific codes (e.g. recording date) or information on individual tracks (e.g. song title, artist). Similar to the audio CD, a track on a DAT tape can be found reliably using the start markers in a fast search. Jump and end marks can also be set so that certain parts of a recording can simply be skipped or the end of the tape "brought forward".
The tape is well protected in its cassette (73 mm × 54 mm). As with the video recorder , the mechanism pulls it out of the cassette housing and - in the form of an "upside down" omega - transports it around the heads. The wrap angle is usually 90 °. As a result, the sound is recorded and read in finite segments that are significantly longer than the width of the tape. The actual tape transport speed is 0.815 cm per second (as opposed to 4.75 cm / s for the Compact Cassette ). However, the head drum rotating at 2000 rpm (usually with a diameter of 30 mm) achieves a relative belt speed of 313 cm / s.
The recording requires almost half a meter of tape material per minute. At the standard tape speed, depending on the tape length, playing times of 15 to 180 minutes are possible. The manufacturers advise against the use of tapes with a length of more than 60 meters as well as the use of DDS tapes ( Digital Data Storage ) for audio purposes, even if this would result in up to 11.5 hours of uninterrupted recording in the DDS-5 tapes Longplay mode are possible. Recordings with double the sampling frequency (96 kHz), however, cut the playing time in half. The cassette is only recorded in one direction.
Playback and recording devices (“DAT recorders”) were originally designed for three sampling rates of 32, 44.1 and 48 kHz , but with 44.1 kHz they could only record analog (artificially limited). After the US and European music companies and the Japanese electronics manufacturers agreed at the end of 1989 to loosen the copy protection of DAT, second generation devices were offered in Germany at the end of 1990 that also record digitally at a sampling rate of 44.1 kHz made it possible to make a digital 1: 1 copy of a CD . In Europe and the USA, however, such devices had to be equipped with the Serial Copy Management System (SCMS) copy protection and only allowed a single transfer from CD to DAT. Copying one DAT to another DAT was still excluded. Other sampling frequencies are 32 kHz, depending on the equipment, with which long-play recordings are also possible (doubling of the playing time when the bit resolution is reduced from 16 to 12 bits with non-equidistant quantization) and 96 kHz for high-quality home and studio equipment. Longplay- and "high resolution" recordings are not using any device compatible . The introduction and subsequent multiple changes to copy protection were justified by fears in the music industry that the possibility of digital lossless copies would collapse the market for CDs.
The uncertainty about whether other, less copy-restricted DAT recorders would come onto the market shortly, made many potential buyers wait and see, given the initially high prices. However, this also did not result in high quantities that could have reduced the price. This is seen as one of the reasons DAT never got beyond a niche existence.
At the end of 1990 there was also a portable DAT recorder, the DATman . It weighed 450 g and had a battery life of up to 2 hours. In 1991 it was offered in Germany for around 1500 DM (corresponds to around 1,234 euros today).
In the studio area there are also devices that work with a resolution of 24 bits. They usually have editing capabilities , timecode and professional XLR connections instead of the RCA connections common with home hi-fi connections (also known as cinch ), which means that they can only be integrated into systems away from a studio to a limited extent. Also there are AES / EBU used -Digitalverbindungen. Many studio devices allow the SCMS bits to be set and deleted and read errors to be displayed. These are typically in the range of 0–50 errors per second; According to a manual from Panasonic, values below 300 are normal. With higher values, either the head is dirty, worn or the tape guide is misaligned. For the related DDS devices, a head drum service life of 100,000 to 200,000 hours (10 to 20 years in continuous operation) is specified, so the head drum should last the entire life of the device.
history
The international DAT conference in 1983 discussed a digital recording system with the aim of a long-term replacement of the compact cassette . The concepts for S-DAT (stationary multi-track tape head) and R-DAT (rotating tape head, as with video recorders ) were developed in two competing working groups . In 1985 the DAT conference recommended R-DAT as the system that could be implemented immediately, despite its complicated mechanics. S-DAT was an interesting alternative, but the production of the multi-track tape heads was not yet technologically controllable. After all, the customer was spared a system war of formats. It was not until 1993 that the S-DAT system DCC ( Digital Compact Cassette ) developed by Philips was ready for the market.
For a time, a small selection of pre-recorded DAT cartridges were offered in retail stores. A selection of the commercially published DAT cassettes, used as sound carriers for music by current artists from this period, can now be researched in the discogs.com database. However, due to the complex duplication and the integrated copy protection, pre-recorded DAT tapes did not achieve any market significance. The format was opposed by the International Federation of the Phonographic Industry for fear of piracy. The potential DAT importers in the USA were threatened with lawsuits worth millions. The DAT conference therefore stipulated the use of double copy protection (blocking copy bit when attempting digital transfer and complete blocking of recording at the CD sampling rate of 44.1 kHz), although this had already been recognized as the reason for a possible setback for the format introduction had been. Ready for series production as early as 1986, the DAT devices remained in the drawer for the time being under pressure from the music industry. In Germany, the first devices could not be purchased in stores until the end of 1987 - limited by the possibility of digital recording from CD. The agreement on the SCMS copy protection system in 1989, which allowed the one-time digital copy, marked a turning point and finally made DAT functional, but in the summer of 1989 the devices still cost around DM 3,500 and a DAT cassette DM 50 Manufacturer DAT recorder on the market. Shortly afterwards, in 1992, DAT devices fell below the DM 1,000 limit in Germany. The format had established itself in the professional sector, where B. was used by broadcasters and the record industry for program exchange and archiving.
With the Profi-DAT devices used there, the audio signal is also output digitally via AES / EBU ; the SCMS is not included there and direct digital copies are possible. The purchase of a CD player with AES / EBU output and a DAT recorder with AES / EBU input, however, were far above the purchase prices of numerous pre-recorded CDs, so that it was simply not worth taking this route for numerous pure digital copies.
DAT received competition in 1991 from the Japanese MD ( MiniDisc ) and soon afterwards from the DCC format, the digital compact cassette . This led to uncertainty among potential buyers. The introduction of the CD recorder for home users in 1995, the serial equipping of personal computers with CD burners , as well as the relatively high purchase price of DAT recorders heralded the end of DAT in the consumer sector. In studios and in the professional sector, however, DAT was able to establish itself well, so it still offers the advantages of a long playing time (of up to 11.5 hours when using a DDS-5 (DAT72) cassette in long play mode), a uncompressed and lossless, high-quality recording and, last but not least, the possibility of building compact mobile DAT recorders.
Thanks to its reliability, DAT was also used by HP as the basis for the DDS format for data backup . DDS quickly found its place as a PC data backup system with a storage capacity of up to 160 GB per tape. DDS cassettes up to and including DDS-5 (DAT72) can usually also be used in conventional DAT audio recorders. No new drives are developed or produced today.
literature
- Helmut Hofmüller: Handbook of home recording. 1st edition, Elektor-Verlag, Aachen, 1998, ISBN 3-89576-044-7
- Thomas Görne: Sound engineering. 1st edition, Carl Hanser Verlag, Leipzig, 2006, ISBN 3-446-40198-9
- Hubert Henle: The recording studio manual. 5th edition, GC Carstensen Verlag, Munich, 2001, ISBN 3-910098-19-3
See also
- Alesis Digital Audio Tape (ADAT)
- Digital Tape Recording System (DTRS)
- Digital data storage
- List of audio terms
