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Thursday, 1 June 2006

Convolution?

Comment I received last night about a piece I wrote: "Is it art or is it for people to listen to?" I sigh just thinking of it. I am an anxious and nervous person. If my music makes you feel anxious and nervous it's because that's how I feel. I probably need meds. Then I could write some happy music. In the meantime, have some noise music. I like noise music.

Why is it that the convolution on SoundHack has absolutely nothing whatsoever in common with the Convolution UGen in SuperCollider? As far as I've ever heard, there is only one audio process with that name. And SoundHack does what I expect. So what is this UGen bullshit? It has absolutely nothing whatsoever to do with convolution. It's like a filter or something. It's garbage. I don't have all morning to waste trying to figure out why my SynthDef isn't working when the UGen is a fucked up piece of shit. Whoever you are Convolution and Convolution2 writer, your UGen does NOT work as advertised! You have wasted my time! (In the future, I should try running the examples in the helpfile before trying to build something, instead of just assuming that things do what they say they do. Or, you know, maybe some people have the mistaken idea that convolution just exists in the frequency domain and were too lazy and annoying to come up with a new name for their related process.)

I feel frustrated. I wanted to make an frustrated piece of convolution. Screaming mixed with gong sound. But I have no real-time convolver. Maybe I could write one with some FFTs.

I am an idiot.

Convolution2.ar(in, bufnum, trigger, framesize, mul, add)

framesize - size of FFT frame, must be a power of two. Convolution uses twice this number internally, maximum value you can give this argument is 2^16=65536. Note that it gets progressively more expensive to run for higher powers! 512, 1024, 2048, 4096 standard.

Yeah, so if I give it a framesize of 65536, I get a nice long gong-y decay and glitches galore as my peak CPU-usage climbs above 600%. (How can you use 600% of something?) Clearly I need a new intel mac, a capybara, a different idea.

Also, to the writer of the Convolution UGens: I'm very sorry I besmirched your UGens. Your helpfile could be a teeny bit clearer though. The link to http://www.dspguide.com/ch18.htm is nice, but it still might be a good idea to mention the implications of the framesize at least in passing.

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