[PD] Combat aliasing!
matju at artengine.ca
Thu Apr 1 02:59:26 CEST 2010
Derek Holzer wrote :
> I was thinking about this the other day.... is it possible to have aliasing
> with Karplus-Strong? Because it's a delay line, nothing is being played back
> at any higher rate than it was sampled at, so no aliasing should be possible.
The aliasing comes from a moiré (interference) between the frequency of the
sampling and the frequency of whatever is going on. In the case of
Karplus-Strong, the choice of the number of samples of delay is an integer,
therefore the rounding of those values will be a kind of aliasing, and this
aliasing will accumulate as the signal is fed back, because all the
fractional-sample delays exceeding or missing are going to add up instead of
being compensated by the usual counters.
If you antialias Karplus-Strong synthesisers, instead, the antialias will act
as a lowpass that will attenuate much of the upper range of possible
frequencies. For example, a delay by n samples and a half, is quite equivalent
to how [rzero~ -1] acts as a kind of low-pass.
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