Dear Editor (Jan. 1972)

Dolbyized FM Broadcasts

Dear Sir: Much has been said in your magazine about the application of Dolby processing to FM broadcasting. The whole basis of Dolby (type B) is to boost treble during low-level passages; the response is then flattened during normal or maximum-level passages.

A complementary device is supposed to be used to de-process the audio. However, should we assume that there will always be level changes sufficient to derive benefit from Dolby processing? In my opinion, the typical rock music FM station will not receive a benefit from Dolby sufficient to justify the expense. How many of you have actually watched modulation meters at a rock station (as I have)? Level changes sufficient to activate the Dolby equipment may represent 1% or less of airtime and on some days they may never happen at all! Many radio stations in this country (rock and otherwise) do not allow drops in audio level; they employ typically 20dB or more of automatic volume-compression and an uncertain degree of manual compression (they "ride the gain"). Such stations pride themselves on being "tight"--which is broadcasting slang for allowing no lapses in audio whatsoever.

Many (if not most) recordings are already highly compressed these days--even many classical recordings. While it is true that Dolby processing may extend the dynamic range of commercial recording, I believe that the final product will always be subjected to compression. This is especially true of rock music where the general rule seems to be to cram in as much subjective loudness as possible.

As a matter of fact, several rock stations on FM in this country are automated and the equipment will automatically reject the very kind of audio which would benefit from Dolby processing! It's called "silence sense" and it's intended to never allow silence on the air because of expired tape or a defective machine. However, this gadget is a troublemaker sometimes because it may reject the occasional soft or slow passage in the music. So, as a matter of self-defense, the tapes for the automation are subjected to lots of automatic and manual compression (and even some clipping) during preparation-then the station compresses it even more on playback. After all this ... it goes to the Dolby. Do you think there will be many level changes on which the Dolby will operate? I think not! Too many of us are guilty of thinking of FM as it used to be. Classical music with wide dynamic range was once FM's specialty. I would like to see a poll taken to determine how true this is today.

I do not believe in the rationalization which says that FM benefits from Dolby even if the complementary receiver circuit is not used. (You could install any kind of "black box" and some people would swear it sounds good.) If the de-processing is not used the response will not be flat at all times.

Isn't a flat response one of the primary objectives of FM in the first place? FCC regulations specify more flatness on FM than on AM. If the FCC rules that Dolby can be used at all times, then they will require that all manufacturers build-in the Dolby circuits in all new receivers. This will render obsolete thousands (perhaps millions) of FM receivers already in use.

Nine out of ten receivers in use cannot easily be converted. Those with separate tuners and preamplifiers could do it easily, but that kind of set is in a very small minority today.

Is all the expense and bother really worthwhile? This change would be made for the sake of a minority of listeners with borderline reception. Let me point out that the FCC (for good reason) limits the range of a station by limiting the power which may be used. It is not logical to use a gadget such as Dolby to extend the range--that's an attempt to bypass the reasons for limiting power.

- Clyde E. Wade, Jr.; Little Rock, Ark.

The basic advantage of the Dolby system is the increased signal-to-noise ratio, and in the recent tests by Chicago's WFMT, a classical music station, listeners in fringe reception areas reported a dramatic decrease in background noise.

Listeners without Dolby decoders were told to adjust their treble controls and the majority of these people said the overall sound quality was improved.

In theory, the service area of a Dolbyized station is increased by a factor of three, and even if we cut this in half, it still leaves quite a sizable minority.

As for distorted program material from many FM stations, Clyde is absolutely right. But if those stations will not derive any benefit from a Dolby system, presumably they will not spend the money!

-Ed.

Pro Playboy

Dear Sir:

Only one word on "Hi-Fi at the Playboy Mansion"--fantastic.

-T. T. Niyaoka Fremont, Calif.

And Con

Dear Sir:

The Playboy article read like a story in a women's (or men's) magazine.

-Bjorn H. Lambrightsen Los Angeles, Calif.

Allison Revisited

Dear Sir:

In his November, 1970, article, "The Loudspeaker/Living Room System." Mr. Allison makes several unwarranted assumptions.

It is true that concert-hall music recordings are closely miked, thereby creating an effect unlike that which the audience normally hears. It is also true, however, that the recording engineers who mix the eight or 16 channels down to two, use monitor speakers to determine the final balance and tone coloration. The result is, in their opinion, a realistic sound. Incidentally, given the combination of different models of monitor speakers and differences in human judgment, the same set of master tracks may come out quite differently when released by two different recording companies.

Another unfair assumption is that all music to which one will listen is concert music. Will all recordings benefit by superimposition of concert-hall acoustic curves? Jazz and chamber music, for instance, are generally heard in intimate surroundings, not concert halls.

Related to these points, however, is the emphasis on natural ambience to allow for derived four-channel sound.

If recordings already possessing concert-hall acoustical characteristics are played back through speakers which duplicate the acoustic response of the concert hall, the response curve is com- pounded. A slope of 5 db at the high end therefore becomes a slope of 10 db, creating an unnaturally dead high-end.

The only reasonable and logical conclusion is that the speakers used in a stereo system should be capable of as nearly flat response as possible. If the speakers themselves are not capable of flat response, use should be made of tone controls or narrow -band equalizer controls to make the net system response as flat as possible. If an imposed effect is called for, concert-hall or otherwise, the controls can be readjusted.

-Philip E. Bond Teaneck, N.J.

Mr. Allison will have an opportunity to reply in the next issue. In the mean- time, I would certainly challenge the assertation that the engineer mixes for the most realistic sound. Not necessarily! He may mix to produce that which, in his opinion, gives the most realistic sound under domestic conditions. Or he may aim for an exaggerated stereo effect, or he may try to achieve an exciting but unrealistic sound It all depends....

-Ed.

(Source: Audio magazine.)

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