Subject: Re: [linux-audio-dev] Ideas for AES/LAAGA/whatever (was Re: sound API libraries, servers, etc.)
From: eli+@gs211.sp.cs.cmu.edu
Date: Thu Apr 26 2001 - 01:06:11 EEST
Jim Peters wrote:
> Regarding a-rate versus k-rate, and how professional synths handle it:
> when changes travel over MIDI, they are definitely stepped, and the
> rate is nowhere near that of the sample-rate, so pro synths must do
> some smoothing automatically to even out the steps.
Some synths do first-order smoothing on MIDI CCs and give you control
over the time constant. At least you want to be able to turn
smoothing on and off. You need it when controlling amplitude, but you
may not want it when controlling frequency.
MIDI CCs aren't really like k-rate, though. There's no sampling rate
defined, so no implicit reconstruction filter, so it's ad hoc whether
you treat them as piecewise constant or try to smooth them. With
k-rate signals you at least know what you ought to do, ideally:
band-limited supersampling up to a-rate.
> I'd like a bit more
> control than the CSound style, though, because a sudden step from 100%
> amplitude to 50% would sound different at different k-rates with this
> approach. At very fast k-rate, you'd still get a nasty click.
If I'm putting in an instantaneous step, I'm asking for a click, so
don't feel guilty about giving it to me. The problem is when I've
sampled my k-rate data from a smooth signal, and a ugen reconstructs
it unsmoothly.
--
Eli Brandt | eli+@cs.cmu.edu | http://www.cs.cmu.edu/~eli/
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