Audio Feedback Loop on LTSP Client

[JacobMcDonald]

I've just finished a clean install of the LTSP edition of 9.10 Karmic in my ESXi 3.5 HyperVisor. I finally managed to get the VM Tools installed for memory ballooning, enhance network, etc. Everything went smoothly.

Next I tried the first PXE boot of an LTSP client. I'm using my Lenovo T60 notebook (Intel T2500 Core Duo, 3 GB RAM, Intel GbE, Intel 945GMA chipset/graphics).

It boots fine and I can login and use applications like normal. However, as soon as the login screen appears I hear a high-pitched audio feedback loop through the speakers.

I figured I would just have to adjust and/or mute the mic volume once I logged in, so I hit the hardware mute button and did just that. But When the mic is muted and even when I change the hardware profile to "Analog Stereo Output" instead of "Analog Stereo Duplex" (thereby disabling the mic control completely), it makes no difference. If I turn the volume down to the point where I can barely hear the audio anyway the feedback problem goes away.

All updates installed as of 2 Nov 2009 and the updated chroot/ltsp has been created.

Linux ltsp1 2.6.31-14-generic #48-Ubuntu SMP Fri Oct 16 14:04:26 UTC 2009 i686 GNU/Linux

[JacobMcDonald (jacob-mcdonaldtechnology)]

I have also posted about this in the Forums:
  http://ubuntuforums.org/showthread.php?t=1312777

[Stéphane Graber (stgraber)]

That unfortunately happens from time to time with some hardware.
I don't think we changed much upstream for that though pulseaudio or alsa may have changed and so cause that issue.

The easiest way to workaround that is to use the lts.conf variables to control these channels.
FRONT_MIC_VOLUME=0 and MIC_VOLUME=0 usually fixes that
otherwise, use <channel name>_VOLUME=0, unfortunately the channel name changes from card to card with no easy way (that I know of) to determine if that's a microphone or not.

[Alkis Georgopoulos (alkisg)]

An attempt to fix this was committed in http://bazaar.launchpad.net/~ltsp-upstream/ltsp/ltsp-trunk/revision/1690.
Marking as "Fix Committed", feel free to reopen this if you still have the problem after applying the fix.

[Alkis Georgopoulos (alkisg)]

Fix released in LTSP 5.2.1.