[alsa-devel] USB Audio questions

Pavel Hofman pavel.hofman at ivitera.com
Wed Aug 17 00:11:55 CEST 2011

Dne 16.8.2011 22:41, Torsten Schenk napsal(a):
> Hi Pierre,
> - The device/driver sends per urb a constant number of packets (as
> you already also discovered). The number of samples per packet differ
> however (+- 1 sample per packet). I accuse the asynchronousity
> between the urb interval and the sound card's internal clock for this
> fact. The device expects the driver to send back an urb with exactly
> the same structure. The device produced crackling noise if the
> samples per packet were not equal. I cannot say to what extend this
> is true (i.e. if you could wait some packets until catching up the
> difference without producing crackles) 

Could we attribute this to the adaptive mode and PLL striving to produce
steady stream of well-timed samples to the DAC? IMHO the lower variation
in samples per packet, the lower jitter of the PLL-recovered clock.


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