Adventures in Surround Sound, from 7.2 to Quad 
(personal and historical notes, basics, and acoustic realities often forgotten)
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Recording in Surround
5mikes line
Five Microphones in a Straight Line

Okay, let's go through the ways one might record a live surround audio session, as a remote or in the studio. Most surround recordings will probably be created during the mixing process, from multitracked sources. That's the same with most stereophonic recordings, and we'd expect to continue with new surround mixes and remixes of older albums. But live recording in the simplest, truly elegant way, tends to produce the most convincing surround recordings. And the lessons learned from doing it directly will act as the best inspiration for what's needed during those elaborate mixdowns.
The first plan above is what I think most of us might want to try among our earliest attempts to record in surround sound. There are five microphones, one per channel, and they're set in a straight-line row as you see here. The mikes can be of several patterns, omnidirectional work well, while cardiods, even bi-directional microphones can be setup this way with great effect. If you've ever fooled with a decent variable pattern mike you know that there's not a huge difference in the sound quality, but more in the way the ambience and intensity of instruments gets recorded. In a bright room you'll probably want a narrower pattern. But in a warm, rich hall or environment, omni's can be pretty special. I've shown a KM-86 Neumann unit in these diagrams, as it's an excellent switchable pattern microphone.
The row of mikes is situated in front of the performers, near or further away much as you'd do for stereo sessions. There might be another group of mikes set up much closer with larger ensembles, which you'd mix in with these main five to enhance or "sweeten" a few of the sources, if needed. I'd suggest trying the ol' kiss principle (keep it simple stupid) for at least some of your earliest experiments, and adjust the mike heights, distances and separations, even mike type, to do the fine tuning. In a classic way the results ought sound pretty wonderful, if everything else is done properly.


5mikes arc
Five Microphones in a 180o Arc

There's a slightly different approach, which you see here. We can place the same five microphones along a curved path, perhaps a full 180 degree arc. The mikes might all be "aimed" straight ahead (if not omni's), or angled outwards somewhat, if the performance to be captured is from a large ensemble. Note that the spacing, as with the first arrangement, is pretty close to equal spacing between all pairs of adjacent channels. The reason for trying this variation is inspired by the ideal way the speakers will be situated on playback. Since we've seen earlier that a semicircular speaker plan is hard to beat, it would only make sense to try a similar configuration while recording. We'll look at a few of the ramifications down below. Otherwise, what applies for the first plan will be pertinent for this second version. Early Stereophonic film soundtracks for Cinerama, CinemaScope and Todd-AO often used this arrangement, before most stereo films were mixed into stereo, using panpots and the usual bag of studio tricks.


5mikes alt
A Common 5-Channel Microphone Array

Another way those early Stereo film tracks were recorded was more like this third version. In most cases the rear-side "surround" track was finally recorded to a single mono track, so a single microphone placed further away from what the camera was looking at was common. This works pretty well, and seems to be a favorite with many five channel surround recordings of classical music. When the LS and RS channels are thought of as rear ambience channels, which is kinda wasteful, but, hey, it's a common notion, the above microphone positioning seems very logical, indeed.
Then the frontmost three channels record a typical closer-miked stereophony, and that's where all the instruments would be heard. The remaining two channels would be picked up with fairly distant mike positions, and so would be relegated to capturing and reproducing the "hall sound", most of the reverberation and echoes from instruments located up front. The spacing then might be different from the first two plans, with equidistant mikes for LF, C and RF, and a much greater distance to both LS and RS, although they would be about the same distance from C, and fairly widely separated.
I think it's mostly a sad way to throw away most of the intense realism and drama that five channel surround audio can provide. If those two channels that cause the most problems, LS and RS are no longer placed behind the listener, then the matching mikes need not be so distant, some of the instrumental forces can be distributed to favor these channels, and the magic of multichannel can be a lot more exciting. I've drawn the third plan to match closely the way many surround systems will be laid out, and for music use, if not film (where the screen IS up in front, not wrap-around Circarama, fer Pete's sake!), this can be a very effective way to go, indeed.

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Quadraphonic Recording
4mikes line
Four Microphones in a Straight Line

There are many musicians who've recently commented that a front center channel is not that important to their music. They've heard how well two decent channels can create "ghost center" effects, when sounds are directed equally to both LF and RF, so see less reason to add more complications to their music mixes by adding a fifth independent channel. at C. This is just a revisiting of Quadraphonic Sound, of course. I've used such a layout for most of my multichannel music, too, as five channel tape recorders were always rather scarcer than "poultry dentistry." So what to do but enjoy what you have, not mourn what you don't have, and may not even need. Meanwhile the rules are changing again for DVD-A's: many multichannel choices have become available.
Anyway, I LOVE the promise of the added C channel, and will not try to rationalize a four-track maximum here, it's now but one choice. At the same time, four channel masters can be "decoded" to extract the in-phase matching level signals which were placed on LF and RF in the original mix, so that the home listener will have unique signals on their new C channel speakers. Many listeners combine their surround system to serve both music and home theater functions. And perhaps still a majority of these home systems do NOT have a discrete center channel, relying on the good old "ghost center" effect. If the speakers are close together to serve a video screen, there won't be a big difference between having a real C speaker or just one of the virtual kind. In that case we really are back to Quadraphony, but doing it the right way.
The four-microphones in a straight line above is what we will probably want to try for our first four channel surround sessions. We'd probably also try a curved arc variation, too, as in the second plan above. Again the mikes can be of many types and patterns, omni or directional, and the same observations of the first plan will apply here, too. The mike stands are a little further apart, to cover the same overall width as before, but that's about the only difference. And there well be the same observation to make down below, if the speakers are not to be placed in a straight line ahead (I've not gone into this earlier, but it is another option to consider, even if it compromises the "wrap-around effect" on playback), but are located in the optimal semicircle.


Creative Quad Recording -- 2 Spaced Mikes + 1 Coincident Pair

When I first began to make remote recordings with that old Viking four-track recorder you saw earlier (and a simultaneous Ampex two track reduction, to play on the local FM radio station and cut stereo dubs for everyone else), I found myself often considering the compromises of the intrusions you might make on a live performance. You really didn't want to annoy everyone, performers and the audience, with a maze of tall mike stands, and lots of cables trailing all over the floor. So it was reasonable to use the same coincident pair mike setups as we had in our two-track remote sessions. At the time I was unaware of the theoretical reasons coincident microphones produce much better, "tighter" stereo images than spaced pairs can do. Stanley Lipshitz authored several fascinating AES papers with audio demonstrations some years back, the definitive one in September 1986, and makes the case very well for NOT using separate, spaced stereo microphones.
Anyhow, there's an opposite side of the coin, too, which Lipshitz mentions. Spaced mikes capture a much better impression of the spaciousness and sound character of the recording environment, at the cost of sharply focussed images. That's why many of the finest recordings of live performances combine BOTH coincident and spaced pairs. But you have to be careful, or you can get phase-cancellations and other disturbing results with multi-microphone pickups (a good rule: let one mike per channel dominate somewhat, don't set them near equal level). On two channels there are a limited number of choices. If we record with multitracks more opportunities arise. The first I thought of is shown above. Trying to avoid a forest of mike stands, my curious audio friend and mentor, Peter Downes, and I mounted a couple of cardiod mikes on a single center stand, then added two extra mikes on smaller stands to either side. We also tried one of the new all-in-one stereo mikes on that center stand. Same idea, two channels from a center position, two from the side mikes. The outer two could be omni or cardiod, the front pair would be directional, cardiod or bi-directional (both work well).
Note how it resembles a three track session to the observer and musicians. And on playback you hear precise imaging between the LF and RF speakers, from the coincident pair, while the other channels are not so sharp in position, but create a marvelous "sense of place," and spaciousness. It's a lovely way to record in four channel surround. You can also extract a C channel later on from the center channels, or use more directional mikes and locate a third mike element along with LF and RF, aimed carefully apart. So this plan can be expanded to include five surround channels. (No, I'm not gonna get into the subtle distinctions between one-axis coincident mikes, versus near-coincident or even slightly spaced "ORTF and NOS like" configurations -- there are subtle trade-offs to each. The images here are just for reference.)


Creative Quad Recording -- 2 Spaced Coincident Pairs

On the other hand, for a major symphony orchestra and chorus Peter and I recorded for broadcast (the Berlioz' Requiem it was, instrumentalists and singers located all around a large cathedral, a perfect subject for surround sound!), this three stand method was not going to work. There was an aisle down the middle of the church, and no place to locate a center stand. No problem, we just shifted over to the above variation. Now both sides of the large orchestra were recorded onto four channels from two short, unobtrusive stands, using TWO coincident mike pairs, a U-48 (facing forwards) and B&O ribbon (facing more to that side) on each stand. (Here's a case that is not directly applicable to five channels, unless you want to add a single C mike between these two stands -- hey, that might work!) You can assume correctly what the results were: excellent side imaging, less defined positions in the center, a good wide sense of spaciousness. What a blast!


cath in

It gets even better than that. We needed more mikes to cover the widely spaced forces, and the Viking deck had two inputs per channel -- eight of 'em! (Well, it used to sound impressive...) So we sneaked in a Schoeps cardioid coincident stereo pair on one tall stand up in front of the main chorus and soloists, which gave excellent focus and positioning (Peter was as crazy as me about trying new ideas out). Then for the auxiliary two choruses and brass ensembles located to the sides, we hid two more omni U-47's, way off to the left and right of the cathedral. So those extra mikes were configured rather like the previous setup above which uses three stands. Still we were not too intrusive, you had to look carefully to see the mikestands dotted around. The theatrical Requiem is composed for major antiphonal forces, and everyone was being very authentic about this unusual performance. It was a marvelous recording experience, one I've never forgotten.
I visited the "scene of the crime" exactly a week ago by amazing coincidence, the first time in some decades, and took the above photos of this beautiful church (as usual click each for bigger views). It's the Providence Cathedral of Saints Peter and Paul. The orchestra and main chorus filled the front spaces completely, the antiphonal brass sections were placed near the side altars (a wedding party is rehearsing in the left one in the photo above) and two additional choruses were over in each side transept, barely visible here. There's also a view of the front of the cathedral, with its sturdy brownstone towers, and the left side facade and entrance. We setup just inside here, carting everything in through this doorway, placing the tape machines on a table in the side passageway. (At the time this plaza consisted of busy city streets and sidewalks.) We'd been able to assemble four Ampex 621 powered speakers (amazing sounding devices for their day), so I was able to monitor with a 120 degree arc of speakers, while Peter and his wife, Maggie, were singing in the main chorus for the Berlioz.
We used a similar setup several times again during my final years at college, and also when I had moved to NYC for graduate school, when I could get away to help Peter with other thorny remote recording sessions. The final remote session we did together was an even more elaborate quad session in the Atlantic City Convention Hall Auditorium (wotta huge barn!), but I've rambled on enough here already -- that's another story for another time...

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Multichannel Recording Quirks
mikes depth
Recording "Depth" Quad (diamond configuration)

Early in this web resource you'll find reference to a long-forgotten suggestion of how to use four tracks for much greater stereo realism, which we've called "Depth Quad." We saw how such a recording could be played back, with a "diamond" arrangement of speakers, all of them up in front, adding a center close and a center distant channel to a wider than usual L and R stereo pair. Let's view the setup to record such a master. It's pretty straightforward. The mikes are in essentially the same locations as the speakers will be. They will probably be spaced further apart, to "scale" up to a larger performing space than our home playback room is likely to be. No matter, it's a one-to-one correspondence.
I realize it might look a little silly here, when I threw in the chair from my studio again to give it scale (ick, the perspective doesn't quite match, nevermind...). But smile as you might at sitting with a mike or speaker in your face, you ought try it out for yourself sometime. After all, we won't see any commercial recordings available using this idea anytime soon ;^)... you'll have to roll your own. It reproduces an uncanny sense of depth, much better than anything we're used to, or about to get used to. But there are tradeoffs as well (not much overall width, and no wrap-around, depth-cues confined mainly to the center). I'm not actually recommending this as our new multichannel system. We'd need at least eight channels to do a convincing job with depth, as described before. And THAT many channels does seem to be premature for the moment. Keep it in mind, though, for a future stage of audio evolution...


rec chorus
Performers and 5 Microphones in Straight Lines

Every good idea has its down side, too. Above we looked at some microphone arrangements that are simple and effective. I'll stand by my suggestions for the optimum final playback arrangement: five channels in a deep 180 degree arc. Still, we might go for the straight line arrangement to record a live performance. It's simple and presents a less cluttered appearance to the performers and audience. Or try one of the alternates described above, with fewer mike stands. Fine, here we have recorded a hypothetical live concert, a small chorus with piano accompaniment, something you might very well get a chance to record in your hometown. Everything goes according to plan, and we bring the master back to our studio (you may guess where this is heading). Start the playback, and here's what we hear:


pb chorus
Reproduces with Illusory Curved Arc Configuration

Suddenly what emerges nice and cleanly out of the monitors is what you see here: a chorus all around in a semicircle, the piano up front and center. It's dramatic and makes for an exciting listening experience. BUT -- it's not what you began with. The relocated five channels have "warped" the soundfield from straight across the front to a wraparound virtual chorus, depicted here. If you go the other way around: curved mike locations (the second diagram above), playback with five speakers in a straight line, the opposite "warping" will take place. To maintain the original configuration of the ensemble, you have to match plans for both mikes and speakers. And in this case, I think you'd hear that a deeply curved pickup of a straight across performance would tend to waste some of the realism of five channel surround, as the LS and RS channels wouldn't be doing their fair share. If surround music is to catch on with the public, let's show it off properly!
Anyway, it is called the recording arts and sciences, isn't it? There's no reason to apologize for the creative side of the act of recording, what effect you must have on the results. There is also no such thing as 100% accurate reproduction, and never will be. If the final product is good fun and an absorbing listening experience, if it conjures up an idealized "real" performance, expanding your own listening environment, who cares? My use of "warping" above is mostly a self-effacing tease. Don't fret the lack of exact match between "whatguzzinta" and "whatcumzouta." The goal is to create the illusion of life, the illusion that everything's identical, and just like making films or animation, you use whatever artifice it takes (those being very artificial art forms).
The reason the speakers ought be situated in one of these simple 180 degree curves is simply to present the maximum audible directional clues, with least wasted or ambiguous information, to the human hearing apparatus. Sometimes you may actually capture nearly what occurred in front of the mikes, and the listeners will hear it that way (depth quad does that in a limited way, and so can binaural sound). Most of the time it will be more complicated than 1:1. But isn't this what cutting edge recording OUGHT be all about, "creating" and "recreating" all mixed-up together, producing wonderful listening experiences that can't be obtained in any other way? Everyone heard the improvements of stereo over mono sound in the 50's and 60's (and two track stereo is very artificial). Everyone does NOT hear the purported "angels on the head of a pin" improvements of gross oversampling and redundant data wasting. Properly done, there will be equally obvious "impact" as stereo had, when we advance to multichannel surround sound. Stick around and join the adventure!

--Wendy Carlos

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