[PD] why overlaps affect frequency of [osc~]?

[Alexandre Torres Porres]

>  [1] https://sourceforge.net/p/pure-data/feature-requests/16/

Not sure if I got what the request was requesting.

"the parameter s->s_sr isn't defined properly, as
s->s_sr=(fs*overlap) has nothing to do with the actual sampling
interval applied to the audio data."

Is this bit just saying overlap in [block~] is done wrong and shouldn't
affect sample rate?

Cause I'd be right there with it...



2013/11/26 IOhannes m zmölnig <zmoelnig at iem.at>

> On 2013-11-26 11:19, Alexandre Torres Porres wrote:
> > Howdy, ever tried to compute a hann window inside a subpatch where the
> FFT
> > is happening?
> >
> > And then if you're overlapping it by 4, do you see that only 1/4 of the
> > cycle from [osc~] came up?
> >
> > That means the [osc~] frequency was 1/4 what it should be...
> >
> > Now, why and how does it happen? I just have no clue at all.
> >
>
> that is mainly because the "sample rate" within the overlapped canvas is
> higher than the sample rate outside.
> (e.g. if you are doing an overlap of 2, you are in fact processing the
> double amount of data in the same time, so your overlapping "sample
> rate" is 88200 if the non-overlapping rate is 44100).
> the same happens if you raise the "samplerate" via "upsampling".
>
>
> [osc~] uses the sample-rate information (within the signal data
> structure) to calculate the phase of a cosine-table lookup.
>
> btw, there has been a long-standing feature request [1] to extend the
> signal-structure to hold both overlap factor and sample-rate, so
> signal-processing objects could handle upsampling and overlapping
> differently.
> (speaking of which, it would also be nice, if any dsp object could have
> a notion of the current overlap cycle)
>
>
> gfmasr
> IOhannes
>
>
> [1] https://sourceforge.net/p/pure-data/feature-requests/16/
>
>
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