[PD] Combat aliasing!

[Pierre Massat]

Wait, so aliasing occurs when the signal is sampled?
So if i have this patch :

[adc~]
|
|
|
[dac~]

and if the signal already contains frequencies above the Nyquist, i will get
aliasing? I generally use my electric guitar as the main audio source, and
i'm assuming that it has lots of harmonics beyond the Nyquist frequency
(especially when the strings are new), yet i never noticed any distortion of
any sort. I might have a bad ear... Or is it just that the energy of the
upper harmonics is too low for me to notice when they cause aliasing?


Pierre

2010/4/1 Matteo Sisti Sette <matteosistisette at gmail.com>

> > Correct, nothing played back at original sampling rate will alias.
>
> It _won't_ alias; it may already _have_ aliased when sampled in the first
> place.
>
> Aliasing occurs when sampling.
>
> When you digitalize (ADC), you are sampling. When generating a waveform
> mathematically, you are sampling the mathematical function at the very
> moment you compute its value at discrete points.
>
> When you play back a signal at a different speed than the original, you are
> _resampling_ it, that is, theorically, interpolating it and then sampling it
> again, and it is the sampling stage, not the interpolating one, that
> produces the aliasing.
>
> The interpolation, since it cannot be an ideal interpolation, may introduce
> other noises or artifacts, not aliasing as far as I can see.
>
>
> --
> Matteo Sisti Sette
> matteosistisette at gmail.com
> http://www.matteosistisette.com
>
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