[linux-audio-dev] jitter on USB audio

[Alfons Adriaensen]

Hello,

A question for the wizards of the USB audio drivers.

At 48 kHz, USB delivers and consumes audio samples in chunks of 48 frames.
When using ALSA's mmap inmterface, these will repackaged to the requested
period size. So one would expect to see a jitter with a range of 1 ms in
the wakeup times of a thread waiting on this interface. For example for
p = 256 the real periods will be 6ms, 5ms, 5ms, 6ms, 5ms, 5ms, ... for
an average period of 5.333 ms.

In practice, when using snd-usb-audio, the jitter range is close to 4 ms.
Why is this, and can something be done about it ?

-- 
FA