A new tape to record your favorite numbers - digital audio tape

INVENTION A NEW TAPE TO RECORD YOUR FAVORITE NUMBERS

It has been just four years since the playback-only compact disc (CD) introduced the music lovers of America to digitally recorded sound, but already a new kind of magnetic tape is rivaling the audio quality of CDs -- and it can record as well as play back. This system, called DAT, for digital audio tape, blends the latest advances in CD, VCR, and computer technology. Like a CD, it provides sound of master-tape quality. Like a VCR, it employs a rotating drum, containing twin re- cording/playback heads, that spins rapidly to permit an extraordinary amount of information to be packed onto a tiny tape 4 mm wide. This keeps speed down to a mere 8.15 mm per second, thus reducing wear on the tape.

In conventional video and audio tape recorders, the heads place an electromagnetic representation of light and sound waves directly onto the tape. In DAT machines, a processing chip designed specifically for the task converts sound into binary digits (bits). This is done by slicing the sound into tiny periods of time. Each of these periods, or samples, is translated into binary digits that represent volume, or amplitude, and pitch, or frequency. The samples are then encoded onto the tape. When it's time to play them back, the system translates each sample into sound, and strings the samples together to re-create the music. You don't hear the seams between them for much the same reason you can't see the gaps between movie frames: both forms of re-creation occur so fast that the senses can't perceive the interruptions. The DAT does its sampling 48,000 times a second -- and each sample is represented by 32 bits (16 per channel).

One reason DATs need so many bits is that they don't record sounds qua sounds, as standard audio cassettes do. Thus extraneous noise is a different and bigger issue for DATs. Tape damage that would be heard as just an annoying hiss or pop on a standard analog machine would be inter- preted as a number on a DAT system, which could translate that number into, say, unwanted forte in the middle of a delicate pianissimo.

For this reason extra information amounting to almost 40 per cent of the original signal is devoted to error correction. The information is used by elaborate microchip-based Reed-Solomon algorithms, devised in the 1960s by Irving Reed and Gustave Solomon, both then at MIT, that check bit patterns for accuracy and interpolate between true ones to re-create those bits obliterated by dust, tape-stretching, and other noise-producing phenomena. If all else fails, the system can mute the sound for a fleeting moment.

Despite its nearly flawless reproduction, DAT isn't music to record companies' ears. The $4 billion-a-year recording industry has grudgingly come to accept home copying with magnetic tape recorders -- which it estimates costs it $1.5 billion annually in lost sales. DATs would permit duplications of unparalleled quality, but audio equipment companies claim to have made digital-to-digital duping impossible: the sampling rate at which DATs record isn't the same as those of CDs and pre-recorded DAT tapes. Nonetheless, the music industry says that audiophiles will be quick to get around this.

The duping issue has touched off a major lobbying war in Washington between the mostly U.S. music biz and the mainly Japanese hardware manufacturers. Says Stanley Gortikov, president of the Recording Industry Association of America, ''The creators of music shouldn't be victims of a new technology, especially when that technology's future is dependent on their music.''

Last August more than 80 electronics manufacturers met in Tokyo to nail down common DAT technical standards. In early October Japanese manufacturers unveiled prototypes of DAT player-recorders and minicassettes (each approximately two-thirds the size of a standard audio cas- sette) at the Tokyo Audio Fair. The American unveiling of these prototypes at the Consumer Electronics Show in Las Vegas in January outraged music industry representatives, who argue that some sort of anti-copying device should be installed in the machines before they're sold. Congress has heard the cries of alarm -- and is now considering legislation forbidding DATs without such duping spoilers.

The music companies' stand may not prove all that wise, if history is any guide. Hollywood succeeded in stalling the pay TV boom from the late 1940s until the 1970s (it was aided mightily in this effort by the technological shortcomings of early pay-TV systems). And the VCR was hardly welcomed by film makers. Yet these technologies created enormous new home markets for movies -- for example, ones too stinko to make a buck in theaters. Sales of pre-recorded DAT tapes, which could be cheaper to make than CDs, could also prove profitable enough to offset piracy losses. In any case, says Marc Finer, an electronics industry consultant, ''the format is so good it's bound to succeed.''

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