German Broadcasting Union
Damns DAT Machines

   According to the New Scientist (15 April 1989), the Institute for Broadcasting Technology, the central research center of the German Broadcasting Union, has published a report that is critical of the digital audio tape (DAT) medium for professional applications. DAT was developed in Japan as a consumer medium. In response to threats from record companies, however, the DAT medium has been marketed worldwide as professional recording format. Before doing so, many companies crippled the format by disabling their capability to record at 
44.1 KHz, the standard sampling rate of compact disks. Hence, tapes recorded at the DAT's standard recording frequency of 48 KHz must pass through a sampling rate converter before they can be mastered for a CD.

    DAT uses a magnetic tape that is 3.81mm wide on which a rotating head lays down closely packed tracks. Each track is 13.6µm wide - about one quarter the width of a human hair.

    Tests conducted by the Institute for Broadcasting Technology showed that DAT machines do not meet minimal professional requirements for digital audio recording systems. In order to pass the IBT test, a recording system must be able to copy a tape ten times without any audible defect.
Also, a tape recorded on one machine must be perfectly playable on another.

    The institute's researchers bought eight DAT machines and made a half-
hour recording on each machine. Then each tape was played back on the same machine three times. No machine was capable of playing back a tape three times in a row without an audible problem. Some machines generated loud clicks on playback that were not present in the original recording.

    To check compatibility between different machines, the institute compared eight professional DAT machines, six domestic DAT machines and five portable DAT machines. Tapes made on one machine would not always play back reliably on another machine.

    The researchers also noticed significant degradation in the tapes when they were subjected to repeated plays. Thus, DAT tapes could not be used reliably as replacements for the cartridge machines used by broadcasters or for any continuous-play application (such as an installation at a museum).

    The only way to make DAT in a reliable, professional format would be to increase the track width to over 20µm. This would mean that the tape speed would have to be increased, which would reduce the playing time of the DAT cassette. Better still, the institute said, DAT manufacturers should scrap the DAT format although and replace the 3.81mm tapewith a larger cassette containing tape that is 6.3mm wide.