[music-dsp] Waveform Interpolation

Peter Schoffhauzer scoofy at inf.elte.hu
Thu Dec 9 08:07:03 EST 2010

andy butler wrote:
>> I too see all interpolation as filtering.
> I don't see how polynomial interpolation a filter, is it?

The same way - it reduces/attenuates the alias images inherently present 
in the digital signal. Olli described this in his long post in other 
words. By definition, a digital sampled signal contains alias images up 
to infinity - the spectrum up to Nyquist is infinitely repeated above 
Nyquist, creating the alias images. I repeat, this comes directly from 
digital sampling, and any unfiltered digital signal played back at any 
frequency will contain these alias images. This is what you hear when 
you zero-order resample a signal, but these artifacts are not created by 
resampling - they're inherently present in the digital signal. Normally 
you don't hear that because your sound card's D/A interpolates the 
signal. Either linear, polynomial or other interpolation will 
attenuate/reduce/filter these alias images. Actually, that's the point 
of interpolation...

- Peter

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