[PD] [ggee/notch] / [ggee/bandpass] seem to work at default/fixed samplerate of 44100

[Raphaël Ilias]

Hi !

Thank you Peter for checking the source code !

Yes I could change my sampling rate.
But, well, I think it's better if pd is able work at different sampling
rates, and many standards now prefer 48KHz to 44.1
 (i.e. digital video recorders).

For now, i'll just make a trick/abstraction that gets the working sampling
rate with [samplerate~] and corrects the frequency parameter by applying a
coefficient (* 44100 / SR)...

However, IMHO, since frequency representation is related to the time and
not the sampling rate, I think this should be corrected in the object
itself, maybe as Alexandros suggested.
But I don't have the skills to do that myself... hope Günther will read
this.

have a nice day,

Raphaël



2015-05-03 5:32 GMT+02:00 Peter P. <peterparker at fastmail.com>:

> * Raphaël Ilias <phae.ilias at gmail.com> [2015-05-02 16:36]:
> > Hello,
> >
> > I was testing the [bandpass] and [notch] object's from "ggee" library,
> > which compute coefficients values for vanilla's [biquad~] and discovered
> > that the center frequency wasn't the one expected, but was shifted
> > something like 10%.
> >
> > After a few measurement I found that the real center frequency was around
> > 1.08841 upwards the ferquency value set to [bandpass] or to [notch]
> > inlets...
> >
> > ...and I later realized that 48000/44100 = 1.088435... and that on my
> > computer, pd is working at 48000 Hz.
> > So, apparently these objects are calculating the coefficients with an
> > supposed samplerate of 44100 Hz.
>
> You are right. I just looked at the source file for one of these
> objects, and it contains a line
>
> x->x_rate = 44100.0;
>
> So apparently the sample rate for it is hard-coded. I don't know ir
> Günther is actively monitoring the pd-list, but perhaps someone else
> here might know how to get that code to be more responsive to different
> sampling rates...
> (you could change your sampling rate to 44100 in the meantime though,
> Raphaël)
> best, P
>
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