As some of you know - and even have affected machines IIRC, some
machines' Internal Mic provides a phase inverted signal, so that summing
left and right channel input results in zero or near-zero output.
I've discussed this with upstream, and the short story is that ALSA
wants it fixed in PA, and PA wants it fixed in ALSA. :-/ Well, it seems
like the best fix is in PA long term, but that is not trivial to
implement and will not reach 12.04.
So, shall we consider kernel workarounds for 12.04? In fact, I started
off my ALSA upstream conversation  with a patch  that mutes the
right channel for the internal mic on Lenovo Ideapad U300s. While I
believe that to be the least ugly workaround, Takashi (upstream ALSA
maintainer) thinks that trading an inverted signal for a muted signal is
trading one problem for another, and does not want to merge it.
I also know it's starting to get late in the 12.04 cycle, but are you
nonetheless interested in merging such a patch for 12.04? If so, I can
make sure the patch applies to the precise kernel, and also write
similar patches for other machines as my time permits. If not, I'm okay
with that too.
Let me know what you think.
David Henningsson, Canonical Ltd.