If you’ve shopped for a new A/V receiver anytime in the past few years, you’ve no doubt seen Audyssey’s logo join the ever-growing collection of silk-screened faceplate emblems. The company’s MultEQ automatic room correction system has quickly become the de facto standard for equalization in home theater, and is included these days as standard equipment on receivers and preamps from Denon, Integra, Onkyo, NAD, and Marantz (View slideshow of Audyssey-enabled receivers). Recently, Audyssey introduced two new sound-shaping technologies to the market, dubbed Dynamic EQ and Dynamic Volume, which take the concept of automatic room correction to the next level. To get the skinny on these new features, we sat down with Chris Kyriakakis, founder and chief technology officer of Audyssey, to discuss their origins and the problems they hope to address.

Let’s talk about Audyssey’s Dynamic EQ feature, which we’ve seen popping up on A/V receivers as of late. How does it work?
Well, Dynamic EQ is an extension of our room correction technology, MultEQ, so let’s talk about that for a minute first. MultEQ was designed after lots of research at the University of Southern California, where I teach along with Tom Holman, one of our co-founders. It’s unique because it was the first [room correction solution] to address how you take sound measurements in a room at multiple positions, and how you combine those measurements to make filters that fix audio problems over a large listening area.

The most common way of doing room EQ is that you put a microphone at your main listening position, play some pink noise, and then you look at the frequency response and make an inverse of that…

In other words, if you find a two-decibel spike at a certain frequency, you counter that with a two-decibel cut at that frequency, and vice versa, in an attempt to flatten out the EQ curve in the room—to make sure that no particular frequency is accentuated over any other...

Right. But there are several problems with that that way it’s been done before. First off, measuring pink noise means you’re only measuring the frequency response—you’re time blind. In other words, you don’t know what part of the signal was direct sound from the speakers and what part of the signal was reflected off of other surfaces.

So to address that problem we came up with a method of measuring impulse responses—bursts of sound—which gives you a lot more information about what’s happening in the room in the time domain. We’re not just adjusting frequencies; we’re adjusting delays, as well. And we come up with the right frequency adjustments and delay settings by taking six or eight measurements and looking at them as patterns: maybe positions one and four give us very similar measurements, for example; that means they have very similar acoustical problems. Positions two, five, and six may also be very similar to each other, but different from one and four. And perhaps the third measuring position is so different that is has a unique response. Based on all of that information, we apply a weighting to the problems. If enough seats have the same problem, then it’s more important than the one seat that has unique issues. And you keep doing that over the entire frequency range, and you come up with this weighted combination, which is better than what others have tried in the past, which was simply taking six measurements and averaging them.

So how does Dynamic EQ fit into the picture?
Well, we’ve found that when you do all of that and equalize a room to a particular target equalization curve, what you’re really doing is equalizing it at what’s called “reference level,” which is the level the person mixing the content was listening to on the mixing stage. But the level at which mixers listen in Hollywood is much higher than “civilian levels,” as we call them. Our installers tell us that the average home user listens at -10 to -20 on the volume knob, and the minute you turn the sound down that far, your perception changes—the balance between bass and mid and treble is completely changed.

This isn’t a new thought, of course: what’s known as “loudness control” came about to address this, and it’s been around for many years. But the reason loudness controls disappeared is that they really weren’t effective.

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