[Bug 412862] Re: AOD250 microphone problem

[Seano]

Somewhere internally the polarity of one of the input sources is
reversed with respect to the other which is causing phase cancellation.

Using either the internal microphone or a mono external microphone
connected to the socket the same signal is applied to left and right
channels (mono mics are usually wired to both pins) so when both are set
to exactly the same level total cancellation occurs.

This can be clearly seen if pavucontrol is installed, the mic level
controls unlocked and one of them adjusted. As it approaches the same
level as the other cancellation occurs then sound returns as it goes
past it.

If a stereo source is applied to the external socket anything which is
the same on both channels is cancelled leaving only the differences.

This seems to be happening with multiple Acer Aspire models but does not
happen when running Windows so is unlikely to be a hardware issue.

My guess is that it is a driver or alsa problem but I have not had time
to investigate further.

Sean.

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AOD250 microphone problem
https://bugs.launchpad.net/bugs/412862
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