[alsa-devel] Delay calculations for USB audio?

[Gabriel M. Beddingfield]

On 09/28/2012 06:00 AM, David Henningsson wrote:
> (Oh, and btw, if you have an idea of the crackling/distorted USB audio,
> let me know. I'm using a standard Logitech USB Headset, using
> speaker-test -c 2 -D plughw:Headset -t sine -r 48000
> I can make the problem go away using any of these options:
>   * Booting a 3.2 kernel - I've tried 3.5, 3.6-rc7 and 3.2
>   * Choosing the 44100 sample rate instead of the default of 48000
>   * Selecting the outer USB port instead of the inner one. Yes, there
> are two USB ports next to each other, and this only happens on one of
> them. (!))

The last statement sounds like you're sharing a hub with another device 
that has reserved bandwidth.  For example, a USB webcam will often do 
this.  Audio will work for a while and then get pre-empted.

Use 'lsusb -t' to view your USB layout.

-gabriel