[pulseaudio-discuss] Questions about timing/sampling reference

Jürgen Herrmann t-5 at t-5.eu
Sat Feb 2 15:22:16 UTC 2019

Hi there!

I'm the developer of Pulseaudio Crossover Rack (
https://t-5.eu/hp/Software/Pulseaudio%20Crossover%20Rack/ ).

During a discussion yesterday evening with an audiophile who owns a five
way horn system some questions arose how pulseaudio handles the timing
and sampling clocks.

a) If a usb sound interface uses adaptive mode, who dictates the
sampling frequency?

b) If a usb sound card uses asynchronous mode it has it's own sampling
clock and tells the computer to send data accordingly, how does
pulseaudio handle this? What happens if two interfaces are connected and
they both use asynchronous mode and the clocks differ slightly?

c) If doing DSP with LADSPA plugins, who dictates the sampling clock
they run at? At which points in the chain will the sampling frequency by
changed and resampling occur (especially when playing material with a
lower sampling rate than the sampling rate pulseaudio runs at)? What
exactly does the daemon config option "avoid resampling" do in this
case? Should this be set to "false" to upsample at the default sink and
use the higher sampling rates throughout if default-samplerate is set to
192k f.ex.?

Best regards and thanks in advance,


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