[pulseaudio-discuss] Virtual audio cable - high cpu usage

Renaud GHIA rghia at tixeo.com
Thu Feb 4 17:29:47 UTC 2021

Thanks for your response.
I understand the problem of clock drift when we have several audio hardware
devices (with different qwartz).
But here, it's a pity that the null video driver has an independent clock...
Concerning pipewire, for now it doesn't work with our particular
application (no sound), but it seems to evolve quickly.
I haven't tried jack for now, but if it depends on pulseaudio, won't I have
the same problem?


Le jeu. 4 févr. 2021 à 00:20, Alexander E. Patrakov <patrakov at gmail.com> a
écrit :

> чт, 4 февр. 2021 г. в 03:10, Renaud GHIA <rghia at tixeo.com>:
>> Thank you for the tip.
>> Now I am sure that resampling does not apply (see below).
>> But unfortunately pulseaudio always consumes 30% of one CPU core!
> The reason is that you are using module-loopback. Due to a potential
> difference between the clocks on the null sink and on the real sound card
> (even though both report 44100 Hz), it always has to resample in order to
> correct for the clock skew. If you don't understand, here is an analogy:
> you have two mechanical watches. Even though both claim that their hour
> hand makes one full circle every 12 hours, in fact, if left unattended,
> they will diverge over time. There is no way to avoid that, except by
> moving to Jack or PipeWire which simply don't introduce a null sink with an
> independent clock.
> If you decide to stay on PulseAudio, you can tweak the resampling method.
> The default, speex-float-1, is light on the CPU resources and should
> produce no distortions detectable by human ear on typical speech and music.
> It does produce easily detectable distortions on specifically crafted
> signals. If you want to make sure that the resampler is transparent no
> matter what is thrown at it, use speex-float-5. There is no point in going
> higher than that.
> --
> Alexander E. Patrakov
> CV: http://u.pc.cd/wT8otalK
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> pulseaudio-discuss mailing list
> pulseaudio-discuss at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/pulseaudio-discuss
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