THE MANY FLAVOURS OF SURROUND SOUND
Last time I was musing that maybe we've made sound processing so difficult that it may not be possible as broadcasters to "get it right" anymore. In particular, I was looking at the variety of formats that Canadian TV stations need to be able to receive and somehow "make comparable" with each other, without spoiling dynamic range and production effects.
A little further looking-around shows that the consumer audio manufacturers are doing everything possible to complicate matters for us. Here then, is a very brief and no doubt incomplete primer of surround sound and high fidelity standards today…
First thing you'll notice in the stereo store is that 5.1 as a consumer standard for home entertainment is already obsolete. I recently found receivers labelled 6.1, 7.1, and even 8.1. Where this is going to end no-one seems to know…
Dolby as a brand name has become pretty ubiquitous, but as a technical description now means too many things to mean anything much anymore… from our old friends Dolby A and B and C (noise reduction standards for audio tape), we've moved on to Dolby Prologic I and II, and Dolby Digital 5.1. When discussing surround sound, however, beware the moniker "Prologic," in either flavour I or II: it means DSP (Digital Signal Processing) black magic, and an attempt to synthesize additional channels from the original mix.
No matter how hard they try, the results aren't remotely the same as an actual multichannel mixdown, and they're bound to disappoint. Typically, what sounds alright with one program has all kinds of weird artifacts with another. The usual artifacts that I notice are low frequency rumble and distortion, the disappearance of centre channel material, phase cancellation of important sources like voices and narration--that kind of thing. Dolby Digital 5.1 was used to describe the genuine article, but it has since begotten Dolby Digital EX, which is also called THX Surround EX, and there's also an extended flavour called DTS-ES. These three are all extensions to the 5.1 standard, to 6.1, or 7.1, or even 8.1, and they're all available in either "matrix" or, more rarely, "discrete." Once again, the "discrete" is the real thing, and "matrix" involves more DSP black magic to attempt creation of even more additional channels where none were before (but without the Prologic name to warn the consumer of the DSP skullduggery).
To mix things up a little more, Sony is still flogging their Super Audio CD, and there's the DVD-Audio standard as well, and both of these have 5.1 flavours as well. These are believed to always be discrete, but what will happen when extensions are wanted for them is anyone's guess. Mine would be more DSP work, which in my opinion would undermine any effort to offer improvement over properly-mastered regular CD's.
In the words of one wag, we can at least be thankful that the original CD standard was made before we had learned enough about digital audio to really muck things up.
Once you have the surround signal decoded, there's still the problem of display, so that the operator can monitor and adjust the audio as needed for consistency. What with levels, phase and frequency content, there's an awful lot of information to present in a meaningful display. Even if we limit ourselves to 5.1 channels, it's clear than you're not going to do very well with a half-dozen VU meters. The equipment manufacturers have arrived with a variety of DSP-driven displays, but so far none have achieved market dominance. Further, we don't know how they're going to react to these "flexible" consumer standards, that keep on drifting to more and more channels. Maybe it's not too late to come up with an update on the classic colour organ for mixdown control!