Subject: Re: [linux-audio-user] ALSA and usb-audio
From: Paul Winkler (pw_lists_AT_slinkp.com)
Date: Wed Jul 31 2002 - 17:50:33 EEST
Hi Joseph, congrats on getting alsa to work with your USB gear!
Sorry you had to be an unwilling pioneer in this area.
On Tue, Jul 30, 2002 at 11:56:42PM -0700, Joseph Zitt wrote:
> However, when I try to play CDs (by selecting CDDA from the menu that
> comes from the box with the little horizontal lines on it), the CD
> plays but stutters, with it sounding like the sound is cutting in and
> out at a steady pace several times a second. Any clues?
You're getting dropouts. Dropouts are commonly a symptom
of the computer not being able to deliver enough audio data
to fill the soundcard buffer before the buffer needs to be played.
Remember that in order to get a continuous stream of sound, the
computer needs to be
Any number of things could cause this to fail:
* not using lowlatency-patched kernel with a realtime-priority app.
In your case, addressing this is probably overkill for playing CDs.
* Output buffers aren't big enough. I would try to adjust this before
trying anything else. I don't have alsaplayer here
at the moment so I'm not sure how you'd adjust buffer size in this case.
Maybe there's a command-line or config option.
Bigger buffers means it takes longer to hear the sound (very bad
for realtime synthesis, but probably quite acceptable for CD playing).
The benefit is the audio is less likely to glitch if CPU usage
gets really intense occasionally, because there's probably time
to catch up before the next buffer period.
* a disk device or data bus can't deliver data fast enough to fill
the audio buffers. How fast is your cd drive?
Are you running other USB devices that send a lot
of data down the USB bus? One way to check would be to set
up alsaplayer to use the built-in laptop soundcard (assuming you've
got that working with alsa). If it works better there, then you
have a problem somewhere in the USB chain. If not, then at
least you know it's not the USB soundcard, driver, or bus.
* The CPU is being asked to do more work than it has time for in each
buffer period. This can happen easily with software synthesizers, even on
high-end modern hardware. I'd be surprised if CDDA extraction caused
this, but try running top in an xterm while you're running alsaplayer.
If cpu usage climbs up to 90 percent or so, you have found the limits
of your processor. Nothing you can do about that but upgrade the
hardware or use less cpu-intensive software.
as a point of reference, I remember running alsaplayer years ago
on a celeron 333 MHz machine with a cheap ISA soundcard,
and the CDDA worked fine, even playing
with the speed control and playing backwards. IIRC you have a PII 266
so I suspect that should be OK.
--Paul Winkler home: http://www.slinkp.com "Muppet Labs, where the future is made - today!"
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