[sdiy] samplers & pitch shifting

rsdio at audiobanshee.com rsdio at audiobanshee.com
Sun May 13 23:35:43 CEST 2018


Hi Scott,

I depends upon how you raise the pitch. If your hardware allows changing the actual output sample rate, then you really don’t have to worry about aliasing unless the sample rate drops too low for a fixed reconstruction filter. One solution is to vary the cutoff frequency of the reconstruction filter so that it always kills everything above Nyquist, as the sample rate changes.

As Monsieur Gillet linked, there is a fine paper on all-digital resampling, which includes an adaptable low-pass.

Brian


On May 13, 2018, at 9:20 AM, Scott Gravenhorst <music.maker at gte.net> wrote:
> Hi Tim and list,
> 
> I'm no expert, but I know that if you raise the pitch of a band limited sample, you
> can still have aliasing unless some technique is used to prevent it.
> 
> What I've done is to use fractional samples taken from the original wave and
> interpolate.  I've never gone beyond linear interpolation and have not found problems.
> This goes for whether it's pitch down or pitch up (assuming that the band limit is at
> a low enough frequency cutoff to prevent alias artifacts.
> 




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