The inverted internal mics

David Henningsson david.henningsson at
Fri Mar 16 08:35:01 UTC 2012

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 [2] with a patch [1] 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.



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