Wednesday, August 5, 2009 at 5:21 pm

I’ve always found recursion amusing and fascinating. I clearly remember my first encounter with one of the more musically common applications of recursion: feedback. When I was quite young, I had one of those fischer-price tape recorders with a microphone attatched to it. I discovered that it would emit this strange, loud whistle when I held the microphone up to the speaker. My father explained to me that the microphone picked up noise the speaker made, and played it back out, louder. Then the microphone picked it up again, and this repeated over and over. This was feedback, he told me. I loved the idea that this weirdly pure-sounding tone could just spontaneously be pulled out of thin air. I would play around with it all the time after that, to the chagrin of my mother, who wasn’t nearly as fond of the noise as I was.

I remember very slowly moving the mic closer to the speaker, noticing how the feedback seemed to “take off” when I got within a certain range. I discovered I could kick start feedback by tapping the mic, even when it was too far to start on its own. Akin to the fine line between genius and madness, feedback is most interesting when you’re right on the border — the boundary between full blast and complete silence. It’s like balancing a see-saw, in that you can never get it perfectly stable… but you can get the see-saw to the point where it takes a couple seconds for it to swing to one way or the other.

Feeding FX back on itself

On an analog mixer, you can get feedback quite easily. Run an aux send’s output back into a channel on the mixer, and then turn up that channel’s level of aux send… instant noise! It gets out of hand quite easily, but with a bit of practice you can get some control over it. It’s much more fun when you add a delay line and some EQ — you can start to deliberately sculpt feedback into something more interesting than piercing whistles. You start to get all sorts of curious ideas: what happens if I feed a phaser back on itself? A nice analog filter? Reverb?

For this reason, though I use the bejeebus out of the aux sends on my mixer, I almost never use the returns. I have FX outputs go into a channel instead, so I can send their output back into themselves… or, even more interestingly, each other. I’ll have drums run out through aux 1 to a filter, have the filter’s output go into aux 2 — a delay — then have the delay’s output go back to aux 1. The feedback comes from not one effect, but both. By fiddling with the aux send amounts, you can navigate around this 2-D landscape of feedback — a lot of feedback from the filter, a bit from the delay… or vice versa, or somewhere in between. Get a couple more aux sends and longer delays involved, and you can sculpt entire tracks from FX and feedback. Even if feedback isn’t your prime source of noise, it can let all your effects bleed into each other; sauces mix and minds meld. Weird, magical stuff happens.

Of course, that’s largely for hardware, analog mixers. Using feedback in this way is much touchier, and less inspiring on the computer. Though it can be done, the boundary between nothing and everything is a thinner, and digital software distortion isn’t nearly as fun as an analog channel strip grunging out. You can make up for this with the careful use of automation and a little patience.

Recursive Audio Bouncing

When I read this interview with Chris Clark, I garnered one really lovely technique from what he said: recursively processing and bouncing a piece of audio:

1. Make a nice drum loop, synth line, whatever
2. Bounce it to disk
3. Manipulate the audio file in some way — run it through FX, reverse it, pitch warp it, whatever.
4. Bounce the manipulated audio file to disk
5. Go back to step 3.

The first couple bounces aren’t usually that amazing: alright, now it’s distorted… alright, now it’s glitched out and distorted… alright, now it has delay…

However, after you’ve bounced it a dozen times or so, chances are the resulting sound will be vastly different from what you started with. With a bit of practice, you start to learn how to take the sound in specific directions. You can nudge a guitar until it sounds like a voice, or vice versa. You can turn any sound into any other sound. I suspect this is what Aphex Twin and Squarepusher mean when they speak of whether or not to Go Plastic — the plasticity of audio when it’s manipulated on a computer. It’s quite liberating and inspiring, once you start to get the zen of it down. Sounds in your head start to materialze in reality faster than you ever thought you could manage. Mind your focus, though, as it’s easy to get lost in the maze of possibilities. Just keep your eye on what you want. Don’t let a neat sound get you off on a tangent; copy the audio off and leave it for later.

You can do this with hardware as well, though it’s much more tedious. Akai’s MPC samplers are particularly great for it.

Making music as a recursive process

We hear a sound, we respond to it, we adjust. Then, we hear the adjustment, respond to the adjustment, and adjust the adjustment. We then hear the adjustment to the adjustment, and our brain turns to goulash….

No, seriously, it’s worth it to mull over your own role in the musical process a little. If a technique works, you use it more. If it doesn’t, you use it less. However, you decide what works and what doesn’t, and this is what makes you different from any other musician. Your choice of processes feeds back on itself, gradually amplifying something deep inside your soul, until it’s loud enough to play on real speakers. This is as magical to me now as that fischer-price tape recorder was when I was five.

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One Comment on “Recursion”

  1. far more applicable for this purpose than the akai mpc (i own/test the mpc1000 with jjos2xl) is the roland spx0x series (the latest is the sp404). very hands on fx, though not at all automatable.

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