[L2Ork-dev] Purr Data & Audio Sample Rate

Albert Graef aggraef at gmail.com
Wed Oct 14 19:14:09 EDT 2020


Hi Joseph,

Well, if you read something into a Pd array at sample rate SR1, and then
play that sample data back later (through Jack or otherwise) at sample rate
SR2, then it will play back with a speedup/slowdown factor of SR2/SR1, and
pitch will shift by the same factor. The audio interface doesn't care where
those numbers come from. It will happily play 48000 samples of your
44.1kHz-sampled data in 1 sec, which will speed it up by a factor of
48000/44100 = 108.8% and make it sound about 1.5 semitones higher.

At least that's what happens if the object decoding the ogg file doesn't
convert to the target sample rate on the fly. I'm not sure whether oggread~
does this.

Joseph, I'm sure you also still remember those glorious days when we
enjoyed playing back those black "LP" discs at 45 rpm. It's the same
effect, only in digital. ;-)

HTH,
Albert


On Wed, Oct 14, 2020 at 10:48 PM Linux ROUEN Normandie <linux.rouen at free.fr>
wrote:

> Hello to the Audio specialists,
>
> I'm struggling since a while with an annoying Audio issue under Purr
> Data using e.g. [oggwrite~] / [oggread~] with their default settings.
>
> Under GNU/Linux for Audio I'm using JACK2 with QJackCtl or Ubuntu Studio
> Control and JACK back-end = ALSA.
> I record from an Audio source (synth, micro, line) with [oggwrite~] and
> then play it back with [oggread~].
>
> As long as I'm using everywhere (Pd, Jack) the same Sample Rate, either
> 44100 or 48000, it's all fine - no issue at all.
> But if the Play SR changes (voluntary or not in Pd & Jack) vs the Record
> SR, then when playing my Audio song back is running either faster or
> slower!
>
> I thought that the Audio SR had nothing to do with the playback speed
> but only, among other things, with the sound quality.
>
> What is wrong in my thinking? Any ideas?
>
> Thank you. Best,
> Joseph Gastelais
>
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-- 
Dr. Albert Gr"af
Computer Music Research Group, JGU Mainz, Germany
Email: aggraef at gmail.com, web: https://agraef.github.io/
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