So, there’s a lot of work in room acoustics where people are thinking about, okay, what makes a concert hall sound great? Can you simulate a concert hall before you build it, so you know how it’s going to sound? And, based on the constraints on those areas, people have used a lot of ray tracing approaches which borrow on a lot of literature in graphics. And for graphics, ray tracing is the main technique, and it works really well, because the idea is you’re using a short wavelength approximation. So, light wavelengths are submicron and if they hit something, they get blocked. But the analogy I like to use is sound is very different, the wavelengths are much bigger. So, you can hold your thumb out in front of you and blot out the sun, but you are going to have a hard time blocking out the sound of thunder with a thumb held out in front of your ear because the waves will just wrap around. And, that’s what motivates our approach which is to actually go back to the physical laws and say, instead of doing the short wave length approximation for sound, we revisit and say, maybe sounds needs the more fundamental wave equation to be solved, to actually model these diffraction effects for us. The usual thinking is that, you know, in games, you are thinking about we want a certain set of perceptual cues. We want walls to occlude sound, we want a small room to reverberate less. We want a large hall to reverberate more. And the thought is, why are we solving this expensive partial differential equation again? Can’t we just find some shortcut to jump straight to the answer instead of going through this long-winded route of physics? And our answer has been that you really have to do all the hard work because there’s a ton of information that’s folded in and what seems easy to us as humans isn’t quite so easy for a computer and and there’s no neat trick to get you straight to the perceptual answer you care about.
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I mean, the basic ideas have been around. People know that, perceptually, this is important, and there are approaches to try to tackle this, but I’d say, because we’re using wave physics, this problem becomes much easier because you just have the waves diffract around the edge. With ray tracing you face the difficult problem that you have to trace out the rays “intelligently” somehow to hit an edge, which is like hitting a bullseye, right?
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So, the ray can wrap around the edge. So, it becomes really difficult. Most practical ray tracing systems don’t try to deal with this edge diffraction effect because of that. Although there are academic approaches to it, in practice it becomes difficult. But as I worked on this over the years, I’ve kind of realized, these are the real advantages of this. Disadvantages are pretty clear: it’s slow, right? So, you have to precompute. But we’re realizing, over time, that going to physics has these advantages.
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