[PD] 4-point interpolation changes timbre depending on sample rate
clemens at chair.audio
Sun May 2 23:28:00 CEST 2021
When there is no aliasing to worry about, i might set the cutoff to pi
On low sample rates (22kHz), the lower cutoff is definitely noticeable.
Btw. I just implemented sharing of the interpolation table of the
delreadsinc~ object according to your suggestions.
It counts the number of references and frees the pointer when no object
uses it anymore.
Am 29.04.21 um 21:03 schrieb Charles Z Henry:
> 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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