[alsa-devel] Clock Drift between hardware sound card and snd_aloop

[Clemens Ladisch]

Rob Nertney wrote:
> I have successfully built a sound capture card that runs at a given rate
> off its own clock. I receive the stream and do some post-processing on it,
> and I want to present this modified data to the user as a capture pcm.

Then you probably want to create an external filter plugin:
http://www.alsa-project.org/alsa-doc/alsa-lib/pcm_external_plugins.html

> I initially thought that snd_aloop would be the best idea, as I can pipe my
> post-processed data directly into it. However, the driver is apparently
> calculating exact timing of what "should" be the rate based off of CPU
> ticks/jiffies and the requested period/sample rate/etc in the requested
> output stream.

Yes; the timing is not synchronized with any other sound card.


Regards,
Clemens