BACK TO THE FUTURE

Unreal Time

Humans can predict the future in ways no electronic circuit can. A recording engineer, for example, can adjust levels not only to match what the musicians are playing at the moment (electronic circuits can do that too), but also to match what those musicians will be playing, before they play it. Those level predictions can be based on familiarity with the music, a reading of the score, or simply a feel for the music's inherent logic-a sense that the music will get louder at a given point because it ought to.

So far, our circuits cannot guess the future-they either know what's coming or they're at a loss. One way circuitry gets such sure foreknowledge is by reading the present while acting on the past. For instance, record-cutting setups often have two playback heads reading the master tape. First the tape passes a head whose output feeds the computer that adjusts the spacing between grooves; about 1.8 seconds later it passes a head whose output feeds the cutter. The first head tells the computer what's coming up in terms of signal volume-and, by extension, how wide the land (area between grooves) will have to be 1.8 seconds (one revolution) hence.

By the time the signal hits the cutter, it's already history to the first playback head.

That sort of thing is easy to do on music already frozen for posterity, like the master tape in the above example. But how can we time-shift live music so our systems can know what's coming? Digital thinking suggests two ways.

Short time shifts are simple. First, digitize the signal (which we will be doing more and more, anyway). Then, pass it simultaneously into a shift-register memory and into the circuits which compute what's to be done with the signal when it comes out of the memory's other end. Using CD's 16-bit samples and 44.1-kHz sampling rate, the memory in a 640K personal computer would be enough to delay a stereo signal by nearly 4 seconds-a long time, to digital signal-processing circuits.

For longer time shifts, it might be necessary to record our digitized signal on some handy medium. Since the signal is not being permanently stored, computer disks would be ideal, allowing any section that's already been played to be immediately recycled back under the recording head. A 5-megabyte computer disk (about the smallest hard disk now available) would hold nearly half a minute of CD stereo.

That would probably be enough advance warning for a level-adjustment circuit to sense where the music's dynamics were heading-to sense, for instance, whether a given loud note was a peak or the start of a long crescendo, and how loud that crescendo might yet get.

This could be done with analog tape loops too, of course. The catch is that each generation of recording on such loops would degrade the signal noticeably. Digitizing would degrade it a lot less-and once digitized, we can record and re record the signal all we want with no further loss. If that signal is going to be digitized in any case, we're home free.

News & Notes

A home optical-disc recorder which will not be compatible with CD-has been announced for limited production by CompuSonics. The DSP-1000 uses 5-inch optical discs which can be recorded once and played indefinitely, but not erased and reused. A two-sided disc can hold about 37 minutes of high-fidelity stereo per side; a data-compression scheme can double that time, though presumably with some loss of quality.

With maximum data compression, the disc can hold 4 hours and 16 minutes of monophonic sound per side, but with an upper frequency cutoff of 6 kHz. Only 25 units were planned for initial production, to sell for $6,995 each. Double-sided discs will cost $175 apiece, and single-sided discs will be $99 each.

A digital recorder with no moving parts has been announced by a London company, Lyric Data, according to The Sunday Times of London. The IXI stores music on computer memory chips, in cartridges which the Times describes as "slightly smaller than videocassettes." The IXI's capacity is 30 minutes, using three such cartridges, each holding 600 1-megabit memory chips.

Presumably, it uses fewer bits per sample or a lower sampling rate than CD, which would require about 850 megabits of storage for 10 minutes of data alone, not counting the memory required for error-correction bits. The price of each cartridge was quoted at about $4,500; no price was given for the IXI recorder.

Direct digital broadcasting began, on an experimental basis, several months ago in Boston. From August through October, WGBH broadcast digital sound over its UHF TV outlet, WGBX, using a Sony PCM-Fl digital adaptor to encode the signal. Listeners with a PCM adaptor and either a VCR, a separate video tuner, or a monitor receiver could receive the broadcasts; WGBH estimates that 200 to 500 listeners in the Boston area are so equipped. The station hopes that this experiment could lead the FCC, now exploring frequency allocations in the upper UHF band, to allocate some of those frequencies to digital sound broadcasting. A digital station would take up about half the bandwidth of a UHF TV channel.

Digital times may be hard ones for recording studios, reports Studio Sound magazine in England. The efforts of record companies are being partially diverted from new recording sessions to CD reissues of LPs.

Equipping a studio with digital recording gear is a big gamble, not only because of its high price but also because no one is quite sure which of two competing digital studio recorder systems-ProDigi (PD) or DASH-will win out. And for those U.S. studios that wait until the dust settles before deciding, the 1987 tax laws may make investments in new equipment less attractive.

Nonetheless, a Sony executive predicts that within two years digital recording will become more common than analog in studios with 24 tracks or more.

While American record companies seek an electronic lockout that will prevent DAT (and possibly analog) cassette decks from dubbing CDs, Kenwood has announced the development of a computer-controlled recording system that will make such dubbing easier. The system would sample CD signals to find a peak level, then set a recorder to just accommodate that peak. This would allow uncompressed dubbing without overload distortion.

Studer and Philips have formed a partnership to develop CD-related studio equipment, including direct CD recorders.

Several Sony "Pressman" portable recorders now have boundary microphones built in; Sony also has announced, in Japan, a recorder that reverses before the tape ends, so as to lose virtually no sound.

The TCM-1000 monitors the speed of the cassette reels to determine when the tape is about to run out.

Sharp has developed a smaller, lighter semiconductor laser for CD players. The company says that players using this laser can be made 1.2 inches thick, 0.4 inch thinner than the current minimum.

A bilateral agreement between the U.S. and Mexico has opened the door to longer hours for daytime-only AM radio stations in both countries.

Stations which formerly went off the air at sundown or 6:00 P.M., whichever came later, may now stay on the air until two hours past sundown. In addition, 321 clear-channel AM stations that were formerly daytime-only may now operate 24 hours a day.

A patent for a direct digital loudspeaker has been granted to Walter E. Stinger, Jr. of Narberth, Pa.

Like other digital speakers which have been patented here and abroad, it is a cellular array. The patent is #4,515,997.

General Electric, the new owner of RCA Corporation, is selling the RCA/Ariola record division to Bertelsmann AG, of Germany; Bertelsmann already owned 25% of it.

The record division had been part of RCA since that company purchased the Victor Talking Machine Company in 1929. Nipper, the fox terrier listening to the gramophone in the famous painting "His Master's Voice," will now have two masters in the U.S.: RCA's consumer electronics division, and the record company.

A cross between karaoke, jukeboxes, and the old "record-your-voice" booths has opened in Houston. At Music Tracks, customers can record their own voices over instrumental and background vocal tracks custom-recorded for the company. According to Music Tracks, 70 songs were available by mid-1986.

For once, an audio development--the BTSC stereo TV sound system-has won TV's Emmy award.

Honors went to Zenith and dbx for inventing it, to the Electronic Industries Association for work on its adoption, to RCA Labs for research and measurements, and to NBC for being first to use it network-wide.

The White Terror

Bob Carver has suggested an answer to my problem of cats clawing speaker grilles and drivers. Whenever he gets in a new pair of speakers, he cues up some white noise and waits for the cats to check out the new additions. Once the cats get close to the speakers, he gives them a blast of noise. Usually that's all it takes to keep them away from those speakers ever after; only one kitten has needed to get the white-noise treatment twice.

To the cats, I suspect, it sounds like the hostility hiss of the largest cat in the world. If you try it, don't do it loud enough to terrorize your tweeters into permanent silence.

Coda: Jack Trux

John H. Trux, Jr., founder and past president of Bang & Olufsen of America, Inc., passed away in September.

Like many prominent audio figures, Jack was also an amateur musician. A jazz drummer, he often followed sales meetings by playing in jam sessions with his staff. After working for Ampex and Bell & Howell (then a maker of tape decks), Jack began importing and selling Bang & Olufsen phono cartridges. In 1970, he founded B & O of America, serving as its president until his retirement in 1983.

(adapted from Audio magazine, Dec. 1986)

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