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Looper's Delight
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At 11:14 AM -0700 10/29/99, Ken Melms wrote: >How did you solve the latency issue?>What OS? What >hardware? If you read the fine print I was careful to say I only dealt with latency in a looping situation, which is a special circumstance. What I meant was, if the computer is only used to output the loop, not any "dry" signal, then my scheme works. If you also want to replace a bunch of stomp boxes and reverbs with software, I agree you are stuck with a fixed minimum delay (the latency) that cannot be turned off. (Although a good fast computer plus a sound card with very small buffers can bring this down to just a few milliseconds.) The idea is pretty simple but seems to be a little hard to believe. Several people said it wouldn't work, and I still doubt it sometimes even after demonstrating it to 40 people. Let's say you want a 10.000 second loop and your computer's total latency (from audio input through the OS, through your application, and back down out to the audio output) is 0.2 seconds-- enough to throw off even a viola player or an accordionist or a guitarist or whatever (duck!). You set up a 10 second delay line, with two delay taps-- one at 10.000 seconds and one at 9.800 seconds. The 10 second tap is used for feedback or regeneration, which happens inside the software every sample so there is no latency problem there. The 9.8 second tap is what you listen to. If you play along in perfect sync with what you hear, it ends up back inside the computer in sync with the 10.0 s internal feedback tap. Note that even though you are technically listening to a 9.8 s tap the delay that you hear, and the total loop length, is exactly 10.0 s. In this scheme the computer's internal sense of "now" is still slightly off from the outside world, but it is nonetheless possible to overdub in perfect sync (barring musicianship like mine, of course!). If this discrepancy bothers you, perhaps for existential reasons, I can't help. But I wouldn't be surprised if our mind-body connections work in a similar manner when we're keeping time anyway. In any case, for me the concept of multiple nows fits right in with my interest in altering time perception through music. Anyway, I worked this out when I had a system with over 300 msec latency, and it took care of that nicely. I am currently using a MOTU 2408 card in a 400Mhz blue-and-white G3 Mac. The latency with this setup is under 6 milliseconds end-to-end, which is less time than it takes for the sound from my speakers to reach my ear. So I'm not sure if it is still worth the trouble, unless you want to get into compensating for the air too. These newer systems make me hopeful that I can eventually get rid of the outboard compressors, distortion, etc. too. -Alex S.