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Old 03-31-2020, 08:42 AM   #8
not-relevant
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Join Date: Jun 2019
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In your example above, is the sampler you're using not simply filling the frequency range it has available to it? I.e. because you're rendering at 88kHz, it's generating output with frequencies up to 44.1kHz, i.e. the Nyquist rate, for 88kHz.

I mean that just because there is energy above 22kHz here, doesn't mean your sampler is broken, just that it is correctly pre-filtering up-pitched samples according to the Nyquist rate for your 88kHz render.

If you were rendering at 44.1kHz, it should be pre-filtering the samples before pitching them up, such that by the time they've been pitch shifted, they contain no frequencies above the Nyquist rate for the target 44.1kHz sample rate.

Basically, if your source sample is at 44.1kHz and you're going to pitch it up an octave, the sampler should pre-filter it to remove content below about 11kHz, then decimate it/interpolate it to basically remove every other sample. The resulting sample is an octave higher, but with no harmonics above 22kHz, and no aliasing should result. Any sane sampler will do this pre-filtering based on the Nyquist rate for the sample rate it's currently running at. I'm not sure your spectrograph proves that the sampler you're using is not doing that

Last edited by not-relevant; 03-31-2020 at 08:49 AM. Reason: Clarify
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