Before we begin to dissect the name “CombFiltered,” I’d like to quote probably the most famous person who has ever discussed my name – Major Nelson at Xbox. In an email exchange we had about it, he said, “That is not at all what I was thinking when we were chatting about it on the podcast. It’s original though, I’ll give you that.” You can listen to the ever entertaining trio of Larry Hryb (Major Nelson), Jeff Rubenstein, and Laura Massey discuss my gamertag on Major Nelson’s podcast and what they thought it meant. Spoiler: they weren’t even close.
Let the mystery build…
For this to make any sense, I’ll need to introduce some audio principles. If you haven’t figured it out already, I’m a nerd.
Any sound that you hear is a series of waves created by moving air. Have you ever seen a subwoofer moving in and out at low frequencies? That’s creating a very large wave, and every speaker does this, just usually to a smaller degree. Waves interact with each other. When these waves interact, weird things can happen.
The basis of all these weird things is waves either increasing or decreasing in volume due to these interactions. How can you get more car rattling bass in a car? Add more subs. When you do this, if you’re smart, you put them next to each other facing the same direction. When you do so, the waves created from both subs interact in such a way that they double in amplitude (roughly). Those waves are now twice as big, and you hear it as louder bass. What happens if you accidentally flipped the wires going to one of the subs? You get in the car, turn it on expecting amazingly loud bass, and you’re pretty sure that it’s now quieter than before. What happened? The waves created from those two subs now effectively cancelled each other out and got smaller. You hear that as a reduction in volume.
Now take this effect across all frequencies – high and low. There is now much more audio information flying all around you in auditory bliss, and you’re much less apt to hear this effect from multiple speakers. There is one very interesting manifestation though, and you can test it for yourself. It’s much more pronounced if you have a home theater system, but it will probably still work on just a TV. Just as long as you have two speakers that aren’t right next to each other.
It’s about to get fun.
Go to the amazing Audio Check website, and play their pink noise test file from a computer hooked up to some speakers (just not headphones). Listen to the 10 second file once so that you know there aren’t any tricks – it’s just noise. Now play it again (it might be helpful to download it and put it on repeat), but this time move your head or walk between the speakers. The more separation between the speakers, the more you’ll hear it. Do you hear a weird effect that develops as you move around? Does it sound like the noise actually changes, maybe gets higher or lower pitched? That’s not the test file – that’s waves of all frequencies interacting with each other between the speakers and your head, cancelling and amplifying at different frequencies, thus changing the actual audio that you are hearing.
This effect is called Comb Filtering. Visually, it looks like this:
This image is used on about every platform for my profile pic. It’s actually a capture from speaker modeling software. The two circles on the left are representations of speakers, and all the pretty colors represent how loud the audio is at a given frequency. Red is loud, blue is quiet. This is the exact same effect that you are hearing from that pink noise test from two speakers, and moving around. Those “spikes” of sound pressure are what you are moving your head around in, and hearing all sorts of weird effects.
So how did I get to CombFiltered from the Comb Filtering effect? Well CombFiltering just didn’t sound cool. CombFiltered – now that’s a name that sounds cool, and makes you stop and scratch your head, wondering what it means…pausing long enough to get sniped down a corridor. Not by me, cuz you just killed me. That’s how you saw my name.