by Edward Tatnall Canby
Time delay! It's the latest thing in listening, though it's been around ever since our recording engineers and broadcasters discovered ambience, via the new microphone, back in the earliest 1930s. Now, delay is digital and for home consumption, direct and to choice, which makes things much more interesting and up to date.
Several years back I reacted with great vigor, as they say, to my first all out experience with this new kind of home facility, the Audio Pulse system--not only for what it could do to astonish the ear via perfectly normal recordings of familiar sorts, but because it also so clearly implied an important change in recording (and broadcast) technique, whereby the producer could no longer control the effects of space and size and ambience in which his music was to be heard in the home.
Since Audio Pulse, there has been the ADS 10 system, which supplies you with everything from built-in 100-watt amps to a second pair of speakers. I've been chafing to try this big system for more than a year but meanwhile, that sober and highly innovative firm, Ad vent Corporation, has produced a more basic digital delay unit for home listening, and it is that one which now adorns my living room, if not quite in the manner Advent intended, as you will shortly see.
Maybe you thought that by this time I must have reverted from four channels back to a solid stereo pair, like al most everybody around. Not so, and I wouldn't actually need the extra gear that ADS so conveniently supplies. A while back, in fact, I beefed up my sys tem by setting out pairs of speakers for each channel, matched, right around the room. Now, prompted by Advent, I've brought in even more-six channels. Everything I had before plus Ad vent too. Works like a charm. After all, if Advent and the others require an upgrade from two to four, then why not from four to six? It took me awhile, I'll admit, to reach that staggering conclusion. But it turned out to be a good answer.
Speaker Saver
As a matter of fact, in case you are one of those who hang on to your old speakers instead of trading them in (how I wish I hadn't sold my Model A Ford for $200 about 1935...), I just made a count and discover that I have no less than 17 speaker systems right now in my living room, and 10 of them actually working. Not to mention the tube-type Motorola AM radio on the table. The silent ones are oldies, dead heading, serving out their time as convenient tables and stands here and there. Most of them could be fired up in an emergency if needed. Nothing very fancy here, you understand--but there's safety in numbers. Just look at the high-priced speaker spreads, all full of multiple woofs and tweets in a single expensive package. Same with me, only separate.
The reason I can still walk around is that these units are stacked up in vertical columns a' la AR 9, two active speakers, one above the other, and sit ting on a third, a silent support, old but sturdy. You'd be surprised how easily these tall, thinnish columns blend into the interior landscape, especially the newer active speakers with those inconspicuous black grilles.
Very great economy of space, I can tell you.
In the back corners, wide apart, I have two of these columns, reaching high so they shoot over my head as I listen. Corner placement helps bass.
Up front are two more identical columns in stereo position, these without the deadhead support and lower down. Floor helps bass. That's 10 units, eight of them active and playing four channels. Now I've added channels 5 and 6, an ad hoc arrangement that just might become permanent. At left middle is another slim column of three speakers, only the top one active, and across the room to the right is its mate standing on top of my equipment cabinet at the same height. All in all, this addition has removed about one more square foot of living room space.
All of these speakers, you must note, are either in matched pairs, or fours.
Necessary if you want sonic stability, whether in six channels or two.
Now about these six channels.
When the Advent Sound Space Control arrived I began with the thought of setting it up just as indicated, two stereo speakers in front and two more for the delay somewhere between the sides and the back, for best effect. The unit passes the "front" signal straight through and adds its subtly variable delay processing to the second set of speakers to make a surround effect.
The back (or side) channels, then, contain all the digitized information in two basic parameters, the length of delay, translating into simulated room size, and the "die-away" or reverb time, which simulates the degree of liveness or deadness in the synthesized space. Both, of course, are abundantly and usefully variable via the controls, as is the volume level of the delayed signals in respect to the front.
Since I had my four channels all set up already, my first thought was simply to disconnect my enhance/logic equipment and reconnect my four channels to Advent's specs. What else? So I did. And I was in business, technically speaking.
But here the argument became confused. Now wait-a-minit, I muttered, this isn't right. I am not com paring the sound of a stereo system to the same with Advent added, which is obviously the intention. Instead, I am comparing two quite radically different means for making use of a full four channels already in situ, installed and operable. Interesting, but-. Moreover, there was no way I could figure to make even this comparison in AB form. In order to install Advent I had to remove the other stuff. So it would be a four-way memory comparison at best--how does this new synthesized digital delay ambience compare with the variable decode-with-logic sound I have been hearing through the selfsame amps and the same four channels of speakers?
Distribution Differences
I think it is important to get straight right here the really profound difference between these two approaches to the same thing. The decode/enhance logic system, via any of the various matrices and the differing logic circuits, once or still available, distributes sound differently to each of the four channels with more or less directional sensitivity, according to clues, mostly phasing and volume differences, that are built into the recording itself. Whether these are controlled by deliberate coding or are casual and random--the delayed reflections of actual room sound and placement as captured in stereo- the principle is the same. The decoders, all decoders, tend to separate the delayed ambience reflections from the direct signals and variably to distribute these around your speaker array, both front and back. There are many formulas for this and, as we remember, even more heated arguments as to which is right and best- no matter. (If you have a choice, you are in the clear.) The principle remains good and useful today.
Those random decoded differences between your four channels, or the deliberately coded differences, do in deed provide a very real and natural sense of room or hall space, not at all unrelated to the original.
The digital delay principle also distributes carefully chosen "reflections" and randomized die-away reverb to your surrounding speakers, for a similar effect of room space and liveness.
But here the idea is altogether different. The delays do not occur at the point of recording- they are created in your living room, out of the whole signal in its stereo form. Thanks to the sophistication- and complication--of current digital circuitry you have very sophisticated controls over the effect, changeable at will. Unlike that of the decode/enhance space, this one can be radically altered in an arbitrary manner. But you are leaving the re cording technician out of the picture! Or you can, if you wish to, ignore him.
You can create a grotesque cathedral sound where the producer had thought of a modest concert hall.
Should you? No law against it, of course.
Synthetic Space What I noticed in my earlier experience with Audio Pulse- not in my own living room- was just this extraordinary versatility, fooling the ears into hearing spaces that were totally synthetic. Crazy! Wonderful. Often grotesque. (That system was operating in six channels as I listened.) With the more circumspect Advent machinery, set up in the very familiar circum stances of my home living room, I noticed right away that here you must be careful. This is NOT a natural ambience. Yet it must not sound synthetic--not, at least, for any sort of extended listening. The built-in ambience of the recording, remember, is still a part of the signal. The recording has its own intended space, large or small, near or distant, live or dead. Out of this, we are building something further. It must be done with reasonable thought, unless we want pure stunt sound. I am quite sure that this is Advent's philosophy and, in the long run, it is good.
On the Advent unit there are indeed a brace of well-mannered controls for the synthesizing. A large variation in the delay time, from 0 to 99 milli seconds in bright red display numbers.
You flip a switch and the numbers race forward or back as the apparent room size gets bigger or smaller. Oddly, al ways one millisecond too low (as if that could matter to you and me!): the maximum is 100 milliseconds at 99 on the display. Decay time, i.e. reverberation time, is controlled by a simple volume-type knob, short to long, making your synthesized space either deadish or liveish as though 20 tons of sound padding were being put down or removed with two fingers. You can also set what I might call the degree of obtrusiveness via a back-channels volume control, which I found vital. Too much is too much when it is overly loud. You can get an optimum balance via a "direct" position, no processing, the same signals in front and in the added speakers, and Advent's directions here are excellent in detail. You can monitor at three choices of input sensitivity via flashing level and over load signals for each delayed channel.
(They indicate a considerable and, no doubt, carefully randomized cross-channel digitalization, an important aid to naturalness.) And yet- I floundered. At first I got all sorts of unpleasant and artificial twangs and buzzes and metallic surges out of the delay speakers. And there was that nasty "door-spring" effect, right out of the early and relatively crude spring-actuated mechanical de lay units! I was pushing too hard. (I had at least to try the stunt aspect.) No go. This Advent, emphatically, is not a stunt machine. It was several days be fore I got over this initial discouragement, for even my first comparisons with a more sober approach were not favorable. I missed the solid, if less controllable, ambience of my regular decode/enhance arrangements, minus all door-springs.
Hang on! I'm not finished yet. When you change brands of car, doesn't the new one often seem pretty cranky, until you get the hang of it? What I learned is, I think, fundamental. In this synthesizing business we need not only moderation but respect. We do have an already built-in and intended effect of delayed sound on every record. Advent can profitably enhance that effect, if you will just listen first, and act accordingly.
To convert a dead studio sound into a cathedral roar is fun but silly. It sounds fake. The Advent really won't take it, though it tries. The machine under this provocation goes into twangs and buzzes at the slightest pop or click or sudden transient and the door-spring sound is always just around the corner. Avoid it! When used properly, all this disappears and the Advent is docile as a lamb. In a word, you enhance what is on your record, you do not change it into something it isn't.
Added Ambience As soon as this dawned on me I knew what to do and Advent's instructions backed me up. Switch the delay channels to DIRECT, or to OFF. And listen to the recording as it is. Get the producer's intention. Then flip back and adjust delay and reverb to suit what you have heard, maybe adding just a bit of extra size and ambience.
There is flexibility, if you understand.
Fairly intimate chamber music (or jazz and pop the same) will not take more than 30 or 40 milliseconds on the delay readout. Most concert music does well from 50 to 75. Reverb (decay time) to taste, but usually no more than half way to maximum. And the whole at a lowish, unobtrusive volume- this is room sound, not the main direct message. Some of the more spectacular recordings, big orchestra and chorus, organ recital, will take up to 90 milli seconds and more--not many! Mostly you must cleave to the original, whatever, and interpret it. That's the whole idea.
Six channels? One night I started thinking. Advent doesn't operate on the regular front channels, the normal stereo sound. So why not hook up both systems simultaneously, taking advantage of an Advent tip that the best place for delay speakers is often at the sides rather than in back. Perfect! Feed the Advent delay into a fifth and sixth channel set up just that way, at the sides. Use the stereo feed-through, or the second main output on my versatile preamp control unit, to feed the decode/enhance equipment as before and so on into the original four channels front and back. The rest is merely switching. Next day the whole thing was done in minutes.
Now I have the advantages of both approaches combined. More than that, I can make any "A-B" test com parison you could possibly want at the push of a button or flip of a toggle. For instance- flip off Advent's delay and you have my old four-way system exactly as it was. Then push "2 CH" on the decode/enhance unit and there's straight two-channel stereo in front only. Flip Advent back on again and I have Advent-only sound, exactly as recommended by the manufacturer, via front and side speakers. Finally, push any of the three decode/enhance buttons and I get full six-channel sound, combining both systems, with variables to taste and all over the place. As they said in the sixties, it's a gas.
I find that in the six-way mode Ad vent works just as it does in four, to widen and open out the matrix-decoded ambience already in the recording and so further enhance the recorded message. Same rules apply, and this is as it should be. All in all, this thin black box with the red flashing numbers is a very useful, high-level gadget to have around.
(Audio magazine, Jun 1979; Edward Tatnall Canby )
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