5.1, 7.1, 9.2, 10.2, 7.3? Where are all those 0.x channels coming from?
At one time there where no 5.1 channel systems, not on film, not in the pro or consumer world. That was before 1987. Before then there was a bit of confusion as to how many channels a film soundtrack could/should have. On stereo optical film there were two real channels, with matrix processing expanded to 4 plus a subwoofer derived from the others. On 70mm magnetic film there were six tracks, which could be deployed in several ways, one of which was 5 screen channels and one surround, another was 3 screen, two surround and one LFE. And that meant your theater had to be reconfigured for whatever film was being shown, something some theaters would do, but pretty much isn’t going to happen in any home.
All that had to end, though, for many very practical reasons. So, at a SMTPE subcommittee meeting in October, 1987, where varyous channel counts and plans where being knocked around, Tom Holman proclaims they needed “5.1”. And everyone looked stunned. Huh?
5.1 is actually a bit of what Holman terms “marketplace rounding error”, because the LFE channel is actually .005 of a main channels sample rate, but 5.005 just doesn’t have the same ring as 5.1
How do you take a marketplace rounding error and give it a life of its own? Easy, you just do. The .1 came to also mean not just the LFE channel of a soundtrack, but also a subwoofer in your HT system. So, 5.1 would be 5 mains, one sub, 5.2 means 5 mains and 2 subs. 7.3 is 7 mains 3 subs… and so on. Thus, the original marketplace rounding error lives and grows larger with each sub. The LFE channel remains a single audio channel at .005 of the sampling rate of a full range channel (240Hz sampling for a 120Hz bandwidth vs 48KHz for a 24KHz bandwidth), even in today’s high resolution soundtracks. It doesn’t become a .2 or a .3, really, ever, even if it’s split out to multiple subs. Yet none add even a Hz to LFE bandwidth. All subs play .005. So all systems should be referred to as x.1 systems, regardless of how many subs you have.
But we all know that’s pretty much not going to happen, because we need a way to gloat over our many-subbed home theaters in a single forceful term. “I got me a 9.4 channel home theater!”
I don’t think there’s been a case of a rounding error multiplied that many times in audio ever before.