A Dolby In the House

By the time you read this, in the fall of 1967, the "Dolby system" will probably be old hat to you. Every other audio publication has been describing it, discussing it, and hailing it as the greatest invention since sex.

We've seen that kind of press ballyhoo before, about such significant advances as the Edsel, the 16-rpm LP and the "thin-profile" loudspeaker, so our first inclination was to be a wee bit skeptical of the Dolby. It seemed too good to be true.

Since then, we've learned more about the Dolby system, and we've listened to some Dolby-ized records with a show-me attitude. And we've been shown. Not only is it entirely as good as it's cracked up to be, it may well be the best news audio perfectionists have had in years.

Just in case you haven't been keeping up with your outside reading, here's a brief description of the why and the how of the Dolby.

Traditionally, recording engineers have had such a phobia of background noise that they would blithely ruin the frequency response and dynamic range of any musical recording if this was felt to be necessary to reduce background noise. And it has often been necessary, thanks to the current commercial practice of duplicating an original tape two to four times over before it is finally used to master a disc. Hiss, print-through, and scrape flutter accumulate with each duplicating step, until the final playback may have as much extraneous noise as an original tape made on a not-too-excellent home tape recorder. The disc itself may have the potential of almost 70dB of Signal/Noise Ratio, but this was hardly relevant in view of the 50–55dB of S/N fed to it by the final "master" tape. Now, finally, the Dolby has changed all this.

Basically a volume compressor-expander (compander), the Dolby has no effect on loud signals, but it raises the level of low-volume signals during the initial recording phase. This compressed recording is then duplicated as often as necessary, and the Dolby is reinserted into the final playback circuit, but this time in the expansion mode. Again, the loud passages are unaffected, but the quiet ones are reduced in volume by the same amount as they were originally boosted. The original dynamic range is restored to the music, but all the accumulated background noises are reduced by 10–15dB, leaving a background of silky silence. And if you've never heard a Dolby-ized disc, you'll never believe just how much noise we'd gotten accustomed to accepting from previous discs.

But as far as we're concerned, the commercial version of the Dolby is only a first, small step. Why not, for instance, include a Dolby expander in the home high-fidelity system, where it can work its wonders on the background noises from our own discs and tapes?

Obviously, at least one manufacturer—KLH—has asked the same question, and plans to answer it soon with the first Dolby-equipped tape recorder ever made for home use. It will compress when recording and expand in playback, and if their necessarily simplified Dolby circuit (the original version costs around $2000) works as they hope it will, KLH's debut in the tape recorder field will produce the quietest tapes you've ever heard.

But why not go a step further, and produce commercial discs and tapes embodying the Dolby's compression phase, but possibly to a somewhat lesser degree? This could neatly resolve a dilemma that has been plaguing record manufacturers and audiophiles alike for years: How to produce a single recording that will satisfy both the narrow-dynamic-range requirements of the background-music listener and the wide-dynamic-range require ments of the serious listener.

The average record buyer would hear pretty much what he hears today. but with somewhat less dynamic range, which wouldn't bother him at all. The Dolby owner, on the other hand, could restore the full original dynamic range (and do away with most of the background noise) for serious listening, or he could shut off the Dolby for background listening. With the Dolby turned on, he could hear the closest thing to live sound that commercial discs and tapes have ever provided, and if that isn't an advance in the state of the art, then we don't know what is.—J. Gordon Holt