Saturday, March 31, 2007

5.1 Channels of Pure Love

I'm finishing up the surround mixes of Millennium Crisis. And I'd become quite concerned with bass management and the Low Frequency Effects (LFE) channel.
For good reason.
The gain structure of the audio in feature films is, as far as I can tell, kinda messed up. In the "mix position" (which is a place which doesn't exist in real life) -20 dB Fs on the recording is supposed to be 85 dB SPL ("C" weighted, measured with band-limited noise) from each channel. So if you're in the middle of the house (presumably the place closest to the mixer's "mix" position was) then each speaker could put out a maximum of 105 dB SPL! And if two speakers had the same in-phase signal, the listener could be hit with 111 dB SPL. If you had the whole system going at full blast then you're up to 117 dB SPL and beyond (that is 4 speakers of equal distance putting out a signal of identical phase at full level -- 0 dB Fs).
This is like being at a Who concert circa 1976. Or the flight deck of an aircraft carrier. It's actually illegal to subject your employees to that much sound pressure level without hearing protection.
To make matters worse, the LFE channel is 10 dB louder on playback than each other channel in the rest of the system! Presumably, this is because of dynamic range limitations on analog optical tracks -- not a big concern in the world of low-budget science fiction anymore.
So -- first of all I think the system is gain-staged a bit oddly. 85 dB SPL should be like -10 dB Fs, and the LFE isn't really necessary in a digital system because you have plenty of headroom anyway. Sure, maybe Tomlinson Holman, whose brain is extra-big, has something vastly smarter to say about this whole matter, but for me it don't really work.

That's what's inspired me to finally go out and get a 5.1 surround system. I'd been thinking for a long time about a Genelec system (minimum price: $2800, maximum price: "whaddaya got?")

But then the light appeared in the sky and the truth lit upon my wracked and weary soul. Blue Sky makes a system called the Media Desk. It lists for only $1300 or so. Oddly, almost nobody has one in stock.

But I found one at Strassberg Associates. Joel set up their floor model for me and I was amazed at how good it sounded. It even comes with a nice remote control. I got the whole thing for under $1000 because it was the floor model (there's a little ding in one of the drivers, I can't hear that it makes any difference). The system is clear and unveiled. It's really much easier to mix on than virtually any system I've heard lately. I can kinda hear the cross-over between the sub and the satellites, but I can't hear the high/mid crossover (and that's the most important.) Maybe when I finally set a good position for the subwoofer the time alignment will be better.

The other thing I decided was to use the optional calibration of 72 dB SPL at -20 dB Fs. This lets us go up much higher in the digital 1's and 0's without shattering our skulls and inflicting permanent hearing damage. Of course, for a theatrical release, someone would have to make the mixes about 12dB quieter.

I'm limiting dialog to -12 dB Fs (that is, 80 dB SPL). Everything else gets mixed around the dialog at that level. So far, that seems to do the trick. Plenty of headroom on top for "boom", loud and clear dialog in the middle.

So -- there you have it. Pandora Machine, Digitalsource, Braidwood Audio, whatever we're calling it these days -- can mix in 5.1. It's official.

Oh and look below! There's an "update" to my biography status!

No comments: