Re: [LAU] lost sound (it had been working)

On Tue, Jan 20, 2009 at 07:48:01PM -0500, Reid Vail wrote:
> I loaded Knopix 5 .1 and the sound worked perfectly right away...and
> that's not a very old version ( < 2 years I think). So then I loaded
> the Ubuntu 8.10 liveCD and it also worked fine.

Interesting, and useful data.

> So this is not a speaker problem or a hardware (MB "soundcard" problem)
> and it's not an old software vs. new software problem. It can only be a
> configuration problem.

Yes, that seems likely, unless your software is different to the Ubuntu
8.10 liveCD kernel, such as may happen if you have applied updates.

> Thinking of trouble-shooting scenario, I wonder if it makes sense to
> reload the liveCD, capture the config and then boot off the HD and
> compare what's in place to what worked on the liveCD? If you think
> that's worthwhile can you let me know which configuration settings to
> capture.

Okay. We've been having this problem on the OLPC XO lately, so I'm up
on it. All the ALSA controls are stored on shutdown and restored on
boot, for most distributions of Linux. The command

"alsactl store" saves the controls, and the command

"alsactl restore" restores them.

There's a --file option for telling it where to store into or restore
from. The default location is distribution specific. Fedora in one
place, Debian in another. Ubuntu is derived from Debian. It is easy to
find, just run the command

        strace -e open alsactl store

On an Ubuntu 8.10 test system here, the file is
/var/lib/alsa/asound.state

The file is text, in my experience, and can be compared with previous
files. The file content is sound card and driver version specific, but
driver authors tend to accept the old file in new versions of driver.
(Gross simplification).

So on the assumption that your problem is ALSA controls, do a store in
each of the operating system environments you have tried, and compare
the output mechanically, e.g. with the diff command. There are some
handy graphical diff programs around, I use kdiff3 or emacs. Capture
all the files first before making any change, so that you can tell why
it is happening.

If you see a difference, try to understand it. Try to restore that file
on the non-working environment. It may fix the problem.

If you see a difference in that there are more or less controls, then
the cause will be change in the driver between the different
environments.

If you see no difference at all, then the cause of your problem won't be
ALSA controls, and you should look at drivers.

There yet may be other causes.

-- 
James Cameron    mailto:quozl@email-addr-hidden     http://quozl.netrek.org/
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