Mysteries of the black box revealed - Rolling Stone
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Mysteries of the black box revealed

Stereo System

Stereo System


It all started when someone had the bright idea of providing a circuit-interruption point—referred to as a tape-monitor circuit—in hi-fi amplifiers and receivers. Originally intended to permit you to monitor tape recordings from three-headed tape decks a fraction of a second after the recordings were made, the tape-out and tape-in jacks also serve as the ideal places to interconnect all sorts of inspired gadgets which can and do improve the sound from your hi-fi setup.

Perhaps the first and best known of the add-ons was the Dolby noise-reduction system “black box,” which, because of its two-part record and play encode and decode process, made the cassette tape deck into a hi-fi component. Now that almost every hi-fi cassette deck comes with built-in Dolby, those extra in-and-out jacks are available for a variety of other black boxes.

As long as records continue to be made of relatively soft vinyl and have to be tracked by hard diamond needles, we’re going to have to live with record scratches. Until recently, that meant having to listen to once-per-revolution clicks and pops that were enough to drive you up the wall. Take heart, discophiles—the SAE company has come to the rescue with a bit of electronic wizardry called the Model 5000 Impulse Noise Reducer—a black box (it actually is black) that, when connected to tape-out/tape-in jacks, actually eliminates the pops and clicks. All you do is push a button, listen to the clicks and pops alone, adjust a lever until you begin to hear the peaks of music and then release the first button. Suddenly, only music comes through, with pops and clicks trapped inside–or so it seems. This amazing device sells for around $200 and is apparently the first in a long line of similar products. In fact, the Plessey Company of England (makers of Garrard record players) has already demonstrated another pop-and-click eliminator which is slated for dealers’ shelves sometime this fall and which will cost even less. The people at Garrard also plan to build the gadget right into some of their turntable systems.

It’s no secret to most hi-fi listeners that most program sources (tapes, FM, discs) undergo some pretty heavy compression when recorded. Tapes can’t accommodate the full dynamic range of music (loudest louds and softest softs), which may reach 80 dB or more in a live performance. And because most discs are made from master tapes, compression of this sort carries over into records, too. FM stations play mostly records and tapes, so what you get by radio is also squeezed together. A company called dbx, Inc., reasoned that something that could be compressed could also be expanded, and, after developing a series of signal-processing equipment for professional studio applications, turned its attention to the hi-fi field. First came a series of expanders, the latest of which, Model 3BX ($650), restores the full dynamic range of recorded music so realistically that you can’t tell it’s operating at all. (The trouble with some earlier expanders was that you could hear them “breathing” or “pumping.”) dbx also offers a series of “companders,” which enable the home recordist to first compress live recorded sounds so they will fit onto tape and then, during playback, expand them back to their lifelike dynamic range. In the process, 30 dB of noise reduction is achieved as an additional benefit. In yet another masterstroke, the company came up with its Model 128 ($450), a gadget that combines the expansion and noise-reduction processes and in effect lets you make tape copies of program sources that actually sound better (have less noise and greater dynamic range) than the originals. Another company in this field is MXR Innovations, Inc., which also has introduced a low-cost compander.

Perhaps the biggest hit of the add-on market has been the graphic equalizer, that multi-levered box which deals with all the frequencies we hear by handling them in several segments. With a graphic equalizer you can tailor overall system response to take care of deficiencies in your room acoustics, one or several components (including the loudspeakers) or just alter response to suit your own ears. Equalizers may have as few as five individual tone controls per channel (each covering a portion of the audio range) or as many as 20 controls per channel. Among the better-known equalizer manufacturers are ADC, Altec, Crown, Dynaco, Heath, JVC, Pioneer, SAE, Sound-craftsmen, Spectro-Acoustics and Lux Audio of America. If you are really serious about getting total response, you can buy a handy equalizer from Shure Bros., the MS-615AS Equalizer Analyzer. It includes a calibrated microphone and an instrument with flashing lights that helps you adjust each equalizer band, octave by octave, until your sounds are all within plus or minus 1 dB of flat at your listening chair. The analyzer costs about $400 (more than many equalizers), but does the job a lot better than most ears.

Two companies we know of, Audio Pulse, Inc., and Sound Design, Inc., continue to offer audio time-delay units which, when added to your system with a small amp and a pair of speakers, can “enlarge” your listening room so that it seems to have the dimensions of a huge concert hall. With these time-delay units stereo signals are delayed as they would be if they were bouncing off the walls and surfaces of a concert hall, and the amount of delay is variable so you can duplicate the feeling of anything from a small discotheque to Carnegie Hall, depending on the type of music you’re playing. Just a few years ago such electronic time-delay systems (used primarily in professional recording studios) would have set you back several thousand. Thanks to integrated solid-state circuitry and other advances, the two units now available cost about $600 each.

In This Article: 1970s, Coverwall, Home Audio


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