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dbx CD player with built-in compression and expansion

technofile  by al fasoldt

Columns and commentaries in a life-long dance with technology
 

Simple gray rule


dbx CD player with built-in compression and expansion
 

By Al Fasoldt

Copyright © 1986, The Syracuse Newspapers

There is little doubt that compact discs have brought quality recordings into the home in a big way. As long as they are made properly, compact discs are noiseless, scratch-free and unflappable - even when the music is playing loud enough to melt Three Mile Island.

But that very ability to play loud and clean has hauled the compact disc into troubled waters lately. Many music lovers have discovered that the huge dynamic range on many CDs cannot be enjoyed under normal circumstances.

If the music is played so that the loudest passages seem just right, the quiet sections often become buried in the everyday noise of typical living rooms. And if the volume is turned up so that those quiet passages are audible, the loud ones can threaten to destroy peace of mind - not to speak of piece of speakers, as they rattle under the burden.

Except for those who are lucky or rich enough to have isolated listening environments and super-rugged loudspeakers, there was no way around this dilemma until now. With a new approach to compact disc playback, a New England firm is offering a way of custom-tailoring the dynamic range of any CD.

The company, dbx Inc., is marketing a unique compact disc player - the $600 model DX3 - that includes a variable compressor. The compressor can be adjusted to cut back on the loudest excursions by as much as 26 decibels (a substantial amount), while bringing up the level of the quietest sounds by 10 dB.

The DX3 has two other special circuits. One, called Digital Audio Impact Recovery, is in some ways the opposite of the compressor, since it makes sounds louder instead of quieter. But the only sounds the DAIR circuit works on are transients - ultra short sounds like drumtaps and piano string impacts - so its effect is to liven up the sound of recordings that were issued from older master tapes.

The third special circuit blends the two stereo channels in either a positive or negative fashion; in other words, it sends signals crosswise either in phase or out of phase. This makes the stereo image narrower or wider.

All three special circuits can be switched out with the touch of a button, returning the DX3 to the status of a typical CD player.

I tested the DX3 in both configurations. When the three circuits were switched off, the DX3 operated and sounded just like most of the CD players I have checked in the last year or so.

Because the DX3 is manufactured for dbx by Nippon Gakki, the parent company of Yamaha, I made it a point to check whether the DX3 shared the outstanding immunity to shaking and jarring shown by Yamaha's players. I found that the DX3, like Yamaha's CD-X1 and CD-X2, would play without skipping even when it was turned sideways or even flipped upside down.

But most of my tests were done with the special circuits in use (and the player right-side up, I might add). The results were extraordinary.

With the "dynamics" knob turned only slightly to the left, so that the compressor was just beginning to work, there was no way to tell the music was being altered except by checking a special meter on the DX3's panel. It showed as much as 15 dB total compression (counting the squeezing of both loud and soft sounds) before its action was clearly audible - a sign of very clever design.

One major benefit of the compressor circuit became obvious when I taped a dozen CDs for playback in my car. In general, I have seldom been satisfied when transferring CDs to cassettes for mobile listening, because road noise made playback a now-and-then affair.

But CDs that were compressed about 20 dB could be enjoyed mile after mile, and they proved equally satisfying when I played them on my high-quality Walkman-type player.

Turning the "dynamics" knob the other way brought the DAIR circuit to life. It made many of my CDs snap into a kind of dynamic focus, especially if they had gone through a couple of copying stages in their transition from master tape to compact disc (a common occurrence, unfortunately).

An "ambience" knob controls the other circuit. Common sense says it should have made little difference, except for varying what is called the "sound stage." But in fact the circuit made a subtle improvement whenever it was turned toward the "+" setting.

My own research and that of dbx's engineers suggests that the circuit creates a pleasing spaciousness in its "wide" setting by duplicating the way phono cartridges reproduce music.

Even the best phono pickups mix the phase of one channel with the other, sometimes in difficult-to-measure ways. It is possible that our ears, conditioned as they are to the sound of phonograph reproduction, prefer such sound to the "straight," non-phasey sound of compact discs. The DX3 is clearly a stand-alone CD player. Even if you were not in the market for a compact disc player, you probably would be fascinated by an audition at a dbx dealer. If you cannot find a dealer close by, write or call dbx at 71 Chapel St., Newton, Mass. 02195. The phone number is (617) 964-3210.


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