[alsa-devel] snd-usb-audio syncronisation problem

Clemens Ladisch clemens at ladisch.de
Fri Feb 22 14:09:14 CET 2008

Adrian Stancu wrote:
> I'm using an E-MU 0404 USB interface with the snd-usb-audio module
> from alsa 1.0.16, operating in isochronous asynchronous mode. This
> interface was producing very annoying click/pop sounds at regular
> intervals during playback. Eventually I discovered that the
> syncronisation mechanism telling the driver to send audio data faster
> or slower to match the interface's consumption speed does not work as
> expected, for some reason.

The momentary frequency as requested by the device is shown in
/proc/asound/card?/stream? (if CONFIG_SND_VERBOSE_PROCFS is enabled).

Try something like:

while sleep 0.3; do grep "Momentary freq" /proc/asound/card0/stream0; done

In theory, once the device has determined its own speed relative to
the computer, this value should be nearly constant.  (When a stream has
just been started, the requested frequency usually is higher because the
device's buffer is empty.)


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