[PD] 4-point interpolation changes timbre depending on sample rate

Charles Z Henry czhenry at gmail.com
Thu Apr 29 21:03:50 CEST 2021

On Thu, Apr 29, 2021 at 12:08 PM Clemens Wegener <clemens at chair.audio> wrote:

> Also: Is it really mandatory to choose a filter cutoff below pi, when the input and output Sample rates match? For a simple static delay that should be the case.

There is an exact requirement when what you're making is an
interpolator:  it has to pass through all the original points!
For that to happen, your interpolating kernel i(t) must have
i(t)=1,   t=0
i(t)=0,  for non-zero integer values of t

An interpolator will have a cutoff freq at exactly pi rad/sec

So, if you're changing the cutoff frequency or amplitudes, it won't be
an interpolator.  It will just be some kind of table reader.
And that's good for performance, I'd say, but your users will have to
know that (and you'll have to justify the choice if it's for an
academic purpose)

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