[alsa-devel] Delay calculations for USB audio?

David Henningsson david.henningsson at canonical.com
Fri Sep 28 13:56:44 CEST 2012

On 09/28/2012 01:23 PM, Gabriel M. Beddingfield wrote:
> 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.

Thanks! Indeed, when deactivating bluetooth (in both kernel 3.2 and 3.5) 
the sound is back to normal, so this time I could actually get the 
distortion out of 3.2 as well.

Question is - is this an actual hardware limitation, or is it actually 
fixable if we wrote better drivers?

David Henningsson, Canonical Ltd.

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