[pulseaudio-discuss] Need help to reduce delay with USB, mic using pulseaudio

[Arun Raghavan]

On Fri, 2011-08-12 at 14:58 +0530, ashwanik wrote:
> Hi Arun,
> 
> Yes, When I use tsched=0 in default.pa, getting low delay but the audio 
> quality is not good as compared to the previous audio(audio with delay). 
> I am getting audio with noise(I think extra noise sample added with 
> audio). I have tried with kernel Version: 2.6.35 & 2.6.38, in both case 
> results are same.
> 
> I tested same usb mic on laptop and its working fine without any delay 
> problem, also tried USB mic with usb headset(playback sink) on 
> pandaboard but delay still persists.
> 
> 
> Please help to figure out where is the problem.

So the problem does appear to be related to timing. You're going to need
to look more closely at the drivers. Since the problem is happening on
USB as well, I'm wondering if there isn't something broken with your
system timers, but that's just a guess.

For what it's worth, Wim Taymans wrote a test module to quantify clock
drift and jitter (but this does use the system clock as a reference).
I've got a recently rebased branch at:

http://cgit.collabora.com/git/user/arun/pulseaudio.git/log/?h=wtay/module-test

This won't help you find (constant-value) bad driver timing reporting,
but will at least be one data point in measuring how bad your timing
information is.

-- Arun