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Posts tagged with 'alsa'

Marcin Juszkiewicz

Call for ALSA UCM profiles

May 11, 2013

by Marcin Juszkiewicz

Under alsa , arm , chromebook , default , fedora , linaro , ubuntu | Comment

When I bought Samsung ARM Chromebook few months ago I had no idea about UCM profiles and burnt speakers (left is dead, right is resting)…

This was good lesson. I learnt more about how UseCase Manager works, took profiles from ChromeOS and added them into Ubuntu so other users will be a bit more safe (due to lack of testers it took months to merge it into “precise” and “quantal” releases).

During last months I had discussions with some Debian, Ubuntu, Fedora developers about how to solve such problems and how to keep UCM profiles shared between distributions.

In meantime Liam Girdwood pointed me to (not used) UCM git tree at ALSA Project server. So finally I spent some time and sent Ubuntu ones for merging.

I also got newer profiles for OMAP4 devices and some updates for Chromebook ones.

The idea is to collect UCM profiles, keep them in one place and share in each distribution packages. So if your hardware has profiles created then join us to make users life easier.

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Colin Ian King

Audio Weirdnesses

November 10, 2009

by Colin Ian King

Under alsa , audio

Yesterday I got poking around a perplexing audio recording issue; quite bizarrely stereo (2 channel) audio from the internal microphone would record perfectly, but mono (1 channel) would not. After working my way down through the driver and though ALSA I got to the point where I could not see how there could be any driver problem, so the issue had to be with the ALSA user space library, or the hardware (or both!).

My colleague spotted an interesting characteristic - using alsamixer to set the capture level to 100% left channel and 0% right channel or vice-versa made the mono recording work. Further investigation by using stereo recording of a pure sine wave (whistling into the microphone!) showed that the left channel was the complete reverse of the right channel. Then the penny dropped - the mono recording was essentially ALSA summing left and right channels, causing a near perfect zero recording since the left channel was the inverse of the right channel. Doh.

As it is, this very same issue has been discussed on LKML here with a suggested workaround described by Takashi Iwai here as follows:

Put the below to ~/.asoundrc

pcm.imix {
 type plug
 slave.pcm "hw"
 ttable.0.0 0.5
 ttable.0.1 -0.5
}

And record using:

arecord -Dimix -c1 test.wav

Urgh. Well, at least there is some kind of ALSA workaround.

So the moral of the story is to twiddle with left and right channel levels and do some stereo recording and look at the results before hacking through the driver. I should have applied Occams' razor - I assumed the complex part (the driver) was the problem.