[PD] Combat aliasing!
matju at artengine.ca
Thu Apr 1 03:05:00 CEST 2010
On Wed, 31 Mar 2010, Mathieu Bouchard wrote:
> 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.
and I forgot to say, if you use [vd~] to circumvent [delread~]'s delay
limitation, you will also find that [vd~] is a lot slower (taking more
cpu), and that's normal, because [vd~] does antialiasing, whereas
[delread~] does not. as a result, you can specify fractionary-sample
delays, and when you do, it sounds similar to changing the setting of
the [lop~] in your feedback loop, because you can't possibly perform
fractionary-sample delay without accidental lowpassing.
_ _ __ ___ _____ ________ _____________ _____________________ ...
| Mathieu Bouchard, Montréal, Québec. téléphone: +1.514.383.3801
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