pulse audio

David Henningsson david.henningsson at canonical.com
Sat Dec 24 04:47:59 UTC 2011

On 12/23/2011 04:08 PM, Len Ovens wrote:
> On Fri, December 23, 2011 5:36 am, Ralf Madorf wrote:
>>> pasuspender PROGRAMMNAME" - http://wiki.ubuntuusers.de/pulseaudio
>> Pardon, it's on German :D.
> Thankyou for the link. I had already found two things that helped.
> Internal mics:
>     In the aspire one netbook(and others with the same chip set) in order
> to use the internal mic. The capture must have the two channels
> unlocked and the left channel set at 0 then use the right level to set.
> Wow, thats intuitive... I'm not sure thats the whole thing because I
> was getting use out of it with both levels the same at least with the
> alpha. I tried this with xubunutu oneric.

This means you have a stereo internal mic where one channel is phase 
inverted. This is not very common, but I've seen it before. In some 
cases, we tweak this by turning it into a mono mic, since we have no 
code for automatic [1] phase inverting in either ALSA, PulseAudio or 
Jack (AFAIK). You can check if this is fixed upstream using 
https://wiki.ubuntu.com/Audio/UpgradingAlsa/DKMS and if it isn't, feel 
free to file a bug for it (using "ubuntu-bug audio") and point me to it.

> Internal mics 2:
>      I don't know why, but... for some reason the internal mic seems to
> have it's own adc. It is set at one speed, in my case 48000. When read
> at 44100 (the default) it sounds staticy because of the mismatch. Kind
> of like under runs I would guess. So on this machine (cheap netbook)
> It is best to set the default to 48000 in the pulse config file. Pulse
> is highly configurable there is no doubt, but figuring that out takes
> some time. I would suspect both ALSA and jack should also be set to
> the native frequency of the sound card (if using the internal sound
> card). Good sound cards don't have this problem.

Hmm, I guess they chose the cheapest possible HDA Codec as well, huh? 
Anyway, this is a problem I've vaguely heard of, but I'm not sure if 
we/upstream have a good solution for this class of problems yet.

David Henningsson, Canonical Ltd.

[1] You can insert manual ttable tweaks in .asoundrc though to turn one 
phase around, but then it might do that for all inputs and not just the 
internal mic, which is not what you want...

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