Alright, i got it! Thanks everybody!
Pierre
2010/4/1 cyrille henry ch@chnry.net
Pierre Massat a écrit :
Wait, so aliasing occurs when the signal is sampled?
yes
So if i have this patch :
[adc~] | | | [dac~]
and if the signal already contains frequencies above the Nyquist, i will get aliasing?
yes, it will. so usually, your sound card have an analog filter prior to digital convertion in order to reduce aliasing.
cyrille
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@gmail.com mailto: matteosistisette@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@gmail.com mailto:matteosistisette@gmail.com http://www.matteosistisette.com
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