Alright, i got it! Thanks everybody!<br><br>Pierre<br><br><div class="gmail_quote">2010/4/1 cyrille henry <span dir="ltr"><<a href="mailto:ch@chnry.net">ch@chnry.net</a>></span><br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<br>
<br>
Pierre Massat a écrit :<div class="im"><br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
Wait, so aliasing occurs when the signal is sampled?<br>
</blockquote></div>
yes<div class="im"><br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
So if i have this patch :<br>
<br>
[adc~]<br>
|<br>
|<br>
|<br>
[dac~]<br>
<br>
and if the signal already contains frequencies above the Nyquist, i will get aliasing?<br>
</blockquote></div>
yes, it will.<br>
so usually, your sound card have an analog filter prior to digital convertion in order to reduce aliasing.<br>
<br>
cyrille<br>
<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div class="im">
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?<br>
<br>
<br>
Pierre<br>
<br></div>
2010/4/1 Matteo Sisti Sette <<a href="mailto:matteosistisette@gmail.com" target="_blank">matteosistisette@gmail.com</a> <mailto:<a href="mailto:matteosistisette@gmail.com" target="_blank">matteosistisette@gmail.com</a>>><div class="im">
<br>
<br>
> Correct, nothing played back at original sampling rate will alias.<br>
<br>
It _won't_ alias; it may already _have_ aliased when sampled in the<br>
first place.<br>
<br>
Aliasing occurs when sampling.<br>
<br>
When you digitalize (ADC), you are sampling. When generating a<br>
waveform mathematically, you are sampling the mathematical function<br>
at the very moment you compute its value at discrete points.<br>
<br>
When you play back a signal at a different speed than the original,<br>
you are _resampling_ it, that is, theorically, interpolating it and<br>
then sampling it again, and it is the sampling stage, not the<br>
interpolating one, that produces the aliasing.<br>
<br>
The interpolation, since it cannot be an ideal interpolation, may<br>
introduce other noises or artifacts, not aliasing as far as I can see.<br>
<br>
<br>
-- Matteo Sisti Sette<br></div>
<a href="mailto:matteosistisette@gmail.com" target="_blank">matteosistisette@gmail.com</a> <mailto:<a href="mailto:matteosistisette@gmail.com" target="_blank">matteosistisette@gmail.com</a>><br>
<a href="http://www.matteosistisette.com" target="_blank">http://www.matteosistisette.com</a><br>
<br>
<br>
<br>
------------------------------------------------------------------------<div class="im"><br>
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