On Thu, Feb 04, 2021 at 06:29:47PM +0100, Renaud GHIA wrote: > >> 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. > > 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? Jack doesn't depend on pulseaudio, it's an independent sound server. Though there are ways to make the two interconnect. As far as I know, jack solves this problem by only allowing one hardware sound device and locking all clocks to that. See: https://jackaudio.org/faq/multiple_devices.html One thing that just occured to me was to ask whether you acutally need to use the remap module at all. I just did a quick test on a very weak machine of mine: a null sink, a music player outputting to that sink, and ffmpeg recording the null sink's monitor-source, all with matching 44.1 kHz sample rates. This resulted in no resamplers in the chain, and only 9% CPU usage on a 2010 Atom CPU. --Sean _______________________________________________ pulseaudio-discuss mailing list pulseaudio-discuss@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/pulseaudio-discuss
