Saturday, December 21, 2013

Organic Limiter

I was just listening and comparing some of the pit mixes I've done and I realized a couple of things.

First was that the "Princess" sound was terribly muddy. Of course, what is available for later listening, and what the audience heard, are different animals, but there's a blurring and a heaviness that I don't think is just an artifact of that particular set of recordings.

In a way it was a given. I had several musicians who were all over the map dynamically. Neither the violin nor the trumpet could make up their minds how far they would be from the mic, either. The only option I had to control all this wildness was excess compression, which takes the bite out of the tone and smothers the articulation and brings up all the unwanted noise higher in the mix -- exacerbated by the loud playing, meaning there was tremendous leakage from one instrument to the microphones on another.

That introduces comb filtering and time smear, again destroying both the tone and the articulation. Once again, a loud pit ends up sounding less good in the end.

But the other realization I had is why running hot gives the illusion of being a solution to mixing ills. The reason is that the ears function as an organic limiter. When you listen at a level above the threshold of comfort (say, if you mix on headphones and insist on having it loud), your ears are unable to follow the peaks. They don't pass the complete sound, and they even shut down slightly in response. But as long as there is sufficient recovery time, the soft parts will still be audible.

So the artifact of mixing with too-hot monitor or 'phones levels is the loud parts are too loud in the resulting mix, and the soft parts get lost. Because your ears have compensated them in. (It will also often have too little bass and top end, again because of those various non-linear responses of the human ear). Typical song structure will start soft, and build, and never quite return to the original level. Mixing at hot monitor levels, this is emphasized; your ears become rapidly fatigued as you enter the louder section, and you keep adding more and more volume through the climax, ending up with a volume curve that looks like the bell of a trumpet.

And the same effect happens with an audience when you run your system hot. The quieter bits are heard because the volume of the entire mix is loud, and the louder bits don't quite read as hyper-loud because of the non-linearities of the ear. But running the human ear with the clip light showing red means it will begin shutting down; as the show progresses, the audience perceives a mix which is increasingly muffled and, basically, softer. This can be temporarily compensated by -- of course -- pushing hotter and hotter.

And with an idiot mixer, the only thing anyone notices is that late in the act they start having "trouble with the microphones." Popping, clothing sounds, feedback. And they wonder if -- since after all they've been performing for all of an hour -- they need to put in fresh batteries.

Once again, science -- physical acoustics, physiology and psycho-acoustics -- reveals what is actually happening, as opposed to the naive perception of the untrained. And once again you as a sound engineer are up against that naive perception. The "I don't care what science says, the second act didn't sound as loud to me. Fix it!" attitude of your directors, music directors, band members, etc.

How to get the hard sell across, so this effect of organic limiting becomes one of the available tools, instead of the apparent (and in reality deadly), panacea?

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