Thorne at the Stereo Society
Thorne at the Stereo Society
Surround Sound: An Introduction
Surround sound has always promised an exciting new music listening experience, but there’s still confusion about it which stands between us and realization of its promises in our homes. Time for a Stereo Society geek-speak-free essay.
Much of our extended-spatial musical options were identified in the early 1970s, when we got all excited about the potential revolution with surround sound. And this was before digital became ubiquitous, the compact disc just a twinkle in the eye of progressive engineers. After reading this introduction, it’s worth checking out the other three historical articles we present, which are from this previous era but deal with the music capture and its production values that still apply today. Notable is a piece from the British Studio Sound magazine by renowned engineer/producer Alan Parsons about the making of the quadraphonic version of Dark Side Of The Moon in the surround sound of the time (then usually called quadraphony). On the classical side is a joint article by the producer and engineer on an enormous Columbia Records classical surround recording, of Schoenberg’s Gurrelieder. A long essay written by Mike Thorne in 1974, Quadraphony and Music explores the musical possibilities of surround sound, with conclusions still very relevant to us now.
The surround sound of the early 70s used four identical speakers, one in each corner, and at first sight this is far more convenient for music and more easily integrated into a living room. However, the surround we have now, to be described in critical detail later, evolved from home theater sound systems and, although it introduces its own compromises and needs two more speakers, in practice it may be easier to integrate into a typical living room.
Back then, there were four methods of feeding four loudspeakers from a vinyl analog disk. All of them were badly compromised, but the hardware industry threw enormous resources behind them. The four heavyweights in the ring all collapsed from exhaustion by 1976. Crucially, the public disliked the standards battle being fought at their expense in their own living rooms, and as a result simply didn’t buy into the idea.
It’s worth looking briefly at these defunct systems before moving forward to today. With 20-20 hindsight, we’re entitled to be amazed at the collective hysteria that made these cumbersome disks seem a commercial possibility to the hardware industry. In fairness, those of us on the production end who had heard the magic of surround really wanted to pass it on and work in the medium, and these four primitive systems could still sound very exciting.
Two of the systems, from CBS (SQ) and Sansui (QS, obviously to avoid confusion), were so-called matrix-encoded systems. The vinyl record looked the same as the standard stereo versions, except that four channels were folded into two by an encoder. In making a record for quad(raphonic) release, in the studio the four discrete audio channels were fed into an encoder which adjusted the relative phase of its two output audio channels (in a complicated way), which were then to be cut on a vinyl disk.
In the home, a decoder picked up the complex phase relationships and produced four independent audio feeds. All well and good in the glossy brochure, but in practice the sounds were not clearly placed and had a disturbing tendency to wander around, sometimes during the short time a snare drum sound would take to die out. If one instrument was playing and another started up, you might hear the first one move somewhere else. Nonetheless, the two matrix systems could give an exciting surround experience, although it often had little connection to the luxurious spatial sound that the engineers and producers had thrilled to in the control room. You can’t get four channels out of two. As the physicists say, there are no free lunches.
In practice, the production team would monitor through four speakers but after feeding the four original audio feeds to an encoder (down to two channels) then through a decoder (back up to the four speakers) so that a mix could be optimized for eventual domestic playback. This wasn’t so much fun for a production crew who could hear what was musically possible but had a demonstration of the limitations of the system thrust at them every time they mixed a quad record. Their reservations fed back to the record companies, who started to get a queasy feeling in the pit of the stomach as they were spending considerable sums to extend routine production to quadraphony.
The other two systems, from JVC (CD-4) and Nippon Columbia (UD-4) added an extra high-frequency disk component over the two front stereo channels, so that the disks could be played either on a regular stereo or through a demodulator that generated the extra two rear speaker feeds. This was a considerable technical challenge. The vinyl needed to be harder, so that the high frequencies didn’t get worn away, and the stylus needed to have much sharper edges so that it could pick up the extra high frequencies. Instead of an elliptical shape, where the sharper curve would touch the two groove walls, it was almost diamond-shaped. Naturally, these were much harder to make and more likely to get chipped in use.
Quadraphony was completely dead by 1977. Most of its potential audience had stayed home. However, around that time the cinema was beginning to introduce surround sound widely. There had been several competing systems, but the most prominent utilized six audio channels fed to multiple speakers ranged around the theater. Another successful system, Dolby surround, used a matrix encode/decode process like the defunct SQ and QS quadraphonic disks, giving a good feeling of surround sound although without the control of a discrete six-channel system.
The surround systems of the theater transferred to the home in the early nineties, as households with both space and money installed what has become a de facto standard, the 5.1 surround system. Ideally, there are five speakers at front left, front center, front right, rear left and rear right. The precise locations of the speakers has been subject to debate, particularly when surround audio (DVD-Audio, then SACD) entered the public’s picture in 2000. Recently, a surround music producer even went as far as insisting that the ‘rear’ two speakers’ ideal music position was different from that for home theater sound reproduction, although I doubt that many enthusiasts will be heaving a couple of speakers around every time they switch between recording and movie.
The .1 in 5.1 is a dedicated low-frequency speaker. Our two ears locate sounds by comparing their slightly different arrival times each side of our head. Low frequencies have a long wavelength (distance between repetitions) which may be too large a distance for our ears to distinguish (roughly, the space between our ears limits the wavelengths whose spatial origin we can detect). So this bass speaker can be anywhere in the room, although obviously the closer you sit to it the more low frequencies you will experience. Its output is considerably higher in power (10 dB) than the other five. The low frequency signal is derived from the other channels.
By now, it must be clear that specifications and definitions of home speaker placements belong to pedants and disconnected theoreticians. Living rooms for human beings are not built to these specifications. A generation ago, stereo magazines would still comment about the ideal positioning of the speakers to deliver a smooth wall of stereo between the two speakers. In practice, the ideal placement depends above all on the room acoustics (and its shape) and on the speakers’ ‘dispersion’, the breadth of the sound beam coming from the speaker. If the dispersion is small, the beam will be narrower and if you move sideways you will be outside it and hear a correspondingly reduced contribution from that speaker.
‘Sonic accuracy’ has little resonance in the recording studio or the home. Control rooms can sound wildly different, but engineers and producers have learned to be flexible. Listening to a familiar recording in an unfamiliar environment for ten minutes is most of what it takes to recalibrate professional ears. There is an undefined standard that record production tacitly acknowledges and that the nonprofessional listener knows intimately. Anyone can notice when a recording is too dull or too harsh. In the home, the most viable standard is whatever sounds the best, which is why we have tone controls on the stereo. The object of all this technology is to have fun in enjoying music as effectively as possible.
That said, the present convenience of home theater playback still leaves much to be desired, and often falls very short for music playback controls. A typical six-channel amplifier takes careful setup, the engineers obviously intending that it be left alone with no instant controls other than source selection and volume. Often, there is no tone controls option to alter easily, frequency response only being adjustable via remote menus applied to single groups of speakers rather than having one knob that changes all. The comparison with user-unfriendliness of the PC is immediate, and it’s to be hoped that a similar transition to easier music functionality will eventually take place.
It’s not necessary to arrange the speakers by the book to get very satisfactory results. In many cases, breaking the rules might give you a better musical sound. The center speaker is important in movies to anchor the dialog and other central dramatic sounds. In music, however, it can reduce the apparent width of the front stereo spread, and the apparent spaciousness of the music is correspondingly lower. Also, the subwoofer is not absolutely necessary, although it sure is fun, and you can’t get the bass oomph without it. With music, you can get by with just four speakers and the results, while not any more or less hi-fidelity than 5.1 can be much more fun than stereo, particularly in a dry acoustic room environment. Stereo recordings played through an amplifier that generates additional signals for the rear speakers can, depending on the processing chosen, yield immersion surround or a sense of reverberation through the back channels, as if you were in a concert hall (of adjustable size). Again, accuracy doesn’t enter into the discussion, but this extra processing can sound very exciting.
Surround sound has finally seen off the old purist classical music arguments that a recording should recreate the original sound. Even at the time of quadraphony, earnest articles would be written about how certain microphone arrangements ‘captured’ the sound field in the performance hall. Fine, but that ignored the existence of the listening room. With surround, the listening room comes to the fore, and we can only optimize our surroundings for the sound we enjoy the most. Any further arguments about speaker placement might be as rewarding as those about whether broccoli or beetroot tastes better.
In 2001, DVD-Audio playback units were appearing slowly. However, the disks cost more to remix for surround, and this is still reflected in disk prices currently higher even than those for a typical DVD video disk.
Of course, there had to be a problem. Sony developed their own SACD audio system, which is incompatible with DVD-Audio, and issued some expensive disks which they first insisted were for ‘semiprofessional users’, whatever that might have meant. After another version of the beta/VHS video cassette format wars of the mid seventies, and similar waste of company resources and your money, SACD is the only man left standing. These disks work on any DVD player, as does any CD. And that’s all, folks. We’ve arrived at our final destination, for better or for worse.