Re: low latency USB audio broken? [was Re: [linux-audio-user] open source firewire]

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Subject: Re: low latency USB audio broken? [was Re: [linux-audio-user] open source firewire]
From: Ryan Gallagher (ruinaudio_AT_comcast.net)
Date: Mon Nov 29 2004 - 01:17:58 EET

On Sun, 2004-11-28 at 15:51 -0500, Lee Revell wrote:
> On Sun, 2004-11-28 at 15:35 -0500, Lee Revell wrote:
> > Can you provide more information? What exactly doesn't work? What are
> > the symptoms?
>
> OK I updated the JACK bug report. Can you (or any USB audio users)
> repeat the test with the latest JACK and ALSA versions (preferably from
> CVS), with both alsaplayer and jackd, at 44100 and 48000Hz? Also please
> try the JACK test in full duplex, capture only, and playback only mode.

Sure, glad to (though I'm not set up to do capture only). Thanks for
taking an interest.

The results with CVS jackd and (very recent alsa 1.0.7) on a 2.6.8.1
kernel with volluntary-preempt are... the same as a year ago.

alsaplayer -r -d hw:1 -f 256 -g 8
alsaplayer -r -d hw:1 -f 256 -g 4
alsaplayer -r -d hw:1 -f 128 -g 8
alsaplayer -r -d hw:1 -f 128 -g 4
alsaplayer -r -d hw:1 -f 64 -g 8
alsaplayer -r -d hw:1 -f 64 -g 4
-all produce clean sound

alsaplayer -r -d hw:1 -f 64 -g 2
- noise

AND running -> alsaplayer -o jack

jackd -R -d alsa -d hw:1
- regular pops and crackle (plus an "aliasing" sound)

jackd -R -d alsa -d hw:1 -r 48000
- regular pops and crackle (plus an "aliasing" sound)

jackd -R -d alsa -d hw:1 -r 48000 -n 3
- clean (plus an "aliasing" sound)

jackd -R -d alsa -d hw:1 -r 48000 -P
- clean (plus an "aliasing" sound)

jackd -R -d alsa -d hw:1 -r 48000 -P -p ( < 1024) -n 3
- regular pops and crackle (plus an "aliasing" sound)

jackd -R -d alsa -d hw:1 -r 44100
- regular pops and crackle

jackd -R -d alsa -d hw:1 -r 44100 -P
- clean

jackd -R -d alsa -d hw:1 -p 512 -n 4 -r 44100
- clean

jackd -R -d alsa -d hw:1 -p 512 -n 2 -r 44100
- regular pops and crackle

jackd -R -d alsa -d hw:1 -P -p 512 -n 2 -r 44100
- regular pops and crackle (somewhat less)

I'm guessing that -> alsaplayer -r -d hw:1 -f 64 -g 4
is analogous to -> jackd -R -d alsa -d hw:1 -p 64 -n 4 -P

So... why can alsa do this low lat playback but not jackd? Wierd.

This leads me to think that this may be a jackd problem more than a
USB/alsa problem, which bodes well for those praying for FireWire
support.

-ry 

-- 
Ryan Gallagher <ruinaudio_AT_comcast.net>

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