Re: AW: usb quattro

[Takashi Iwai <tiwai@suse.de>]

At Sat, 07 Sep 2002 05:40:02 +0900,
Patrick Shirkey wrote:
> 
> Takashi Iwai wrote:
> 
> >>the Tascam US-428 driver (copied / changed from snd-usb-audio ) showed a
> >>similar problem.
> >>I worked around it by not using ASYNC_UNLINKing of the urbs.
> > 
> >  
> > yes, this could be the problem.
> > this happend once and i thought it fixed on the alsa side, but it
> > seems that there is something wrong on usb driver itself.
> > why it happened on jack is because jack caused xrun - and the driver
> > tries to stop the stream and unlinks urbs with ASYNC_UNLINK flag.
> > 
> > anyway, i changed the code on cvs to use SYNC unlink mode as default.
> > this may have a drawback that the urbs still exist even if the driver
> > stops the stream after detection of xrun.  but usually this doesn't
> > matter so much.
> > 
> > i've tested normal playbacks and it seems working.
> > 
> > 
> 
> I have actually managed to get a stream from alsaplayer through without 
> a hang but the sound is choppy.
> 
> I will make a test signal  so you can hear what I am getting. It's 
> similar to what was happening before the driver was fixed last time.
> 
> I got this output from jackd. this happened after I started jack and 
> didn't connect any other apps. Maybe it timed out but I don't think it 
> is supposed to.
> 
> ----
> $ jackd -v -d alsa -d q4
> jackd 0.37.1
> Copyright 2001-2002 Paul Davis and others.
> jackd comes with ABSOLUTELY NO WARRANTY
> This is free software, and you are welcome to redistribute it
> under certain conditions; see the file COPYING for details
> 
> 512 waiting for signals
> creating alsa driver ... q4|1024|2|48000|swmon

the resolution of usb-audio device is 1ms.  this value is fixed.
thus you need to adjust the period size according to the sample rate
if you want to achieve the real-time response with a small period
size.

that means:
- the sample rate should be 48kHz (or 32kHz), which can be divided by
  1000, and should not be 44.1kHz.
- the period size should be aligned to (rate / 1000).
  in the case of 48kHz, the period size should be 48, 96, 192, ...

please try this combination.


Takashi


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