thanks master

well, I was betting it was that, and it actually brings me to more direct questions I should have asked before. So here they go.

Simply put: How come and why does overlapping affect the sample rate?

> the same happens if you raise the "samplerate" via "upsampling".

I guess this is what's really confusing, cause I can't seem to get it.

If you do upsampling with block, for instance, you don't get this frequency change issue with [osc~]. It'll run the same frequency, no problem... but overlapping will do that somehow.

Why the hell the actual upsampling does not affect it?

And does this mean that overlap of 4 and upsampling of 4x makes it really run at 16x the sample rate? 

cheers


2013/11/26 IOhannes m zmölnig <zmoelnig@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/


_______________________________________________
Pd-list@iem.at mailing list
UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list