pulse audio

David Henningsson david.henningsson at canonical.com
Mon Dec 19 23:56:57 UTC 2011

On 12/19/2011 08:49 AM, Len Ovens wrote:
> Any way we can get rid of pulse audio?

Do you have a better replacement? If not; please keep a friendlier tone. 
I'm not saying PulseAudio is perfect, but it is still the best 
general-purpose sound server out there, AFAICT.

> Installed todays version of US (no
> new problems) to try out some audio stuff. Installed audacity on top for a
> quick and easy audio recorder... straight into alsa via pulse. This is my
> netbook, so just the on board sound stuff which I had noticed before is
> quite noisy. I'm not sure if there is a setting somewhere I can change
> this...

I don't know how the XFCE mixer app works, and what you can or can't do 
there, but you can certainly change the current routing in the 
"pavucontrol" application. While your application is recording, go to 
the "recording" tab in pavucontrol.

>  but two things. I never did get anything out of the built in mic.
> (not a big loss as I recall, but pulse does have a switch to switch
> between mic and input) It is the standard intel sound, but I guess there
> are variations.

This is very likely a driver problem, unrelated to pulseaudio.

> The big problem seems to be that pulse tries to be too intelligent. There
> is a capture level and a mic boost level according to alsamixer. If I
> leave pulse set to line, mic boost is 0 and pulse controls capture...
> Good. But as soon as I switch to mic... still with an external mic. Now
> the pulse level controls both the capture level and the boost level... it
> seems to do them at the same time... the boost level seems to only have 8
> setting (16 maybe?) but capture is a lot more (128?) So capture reaches 8
> out of 128 when boost is full... BAD really BAD.

Why is this bad? If you tell PulseAudio to achieve +30 dB, whether 
PulseAudio chooses to set "Boost=+30 dB, Capture=0 dB" or "Boost=+12 dB, 
Capture=+18 dB" should lead to equivalent results. If anything, having 
boost high and capture down should theoretically lead to better quality 
as the signal level would be higher between the "boost" (which comes 
first) and "capture" volume controls.

However, it does not seem to be that way in your case. I don't know why, 
but I haven't heard of it before. Also likely a driver/hw problem, not a 
PulseAudio problem. I would guess that it is more common to achieve the 
best quality by having boost up and capture down though.

Anyway, you can change that behaviour by changing 
/usr/share/pulseaudio/alsa-mixer/paths/analog-input-mic.conf and change 
the order of the [Element Mic Boost] and [Element Capture] sections.

> So I manually set boost
> low and capture full so that the meter in pulse shows what looks like a
> reasonable level. Ok, now start audacity recording... this opens a port in
> pulse, pulse looks at the level it has and translates it to how it does
> things and mic boost is now full and capture is half and the recording is
> noisy... Yuck! OK, delete track, put audacity in pause and record... pulse
> goes nuts... while in pause set my levels... capture full and boost at 1
> notch. Hit pause to roll. Sound is much, much cleaner... quite good
> considering the mic is one of those things attached to my headset.
> What pulse audio should do... is use the capture level from 0 to 128 and
> then use the few boost setting on top of that. Too notchy for a good fade,
> but that can be done inside audacity or ardour... complete with
> automation. Would this be a bug or a design decision in pulse? It seems to
> know what the controls it is playing with are as it only uses the boost in
> the mic setting. The only advantage I can see is that one gets better
> granularity the way they have it. I'll take sound quality thank you.
> Problem two (or is that three?) once pulse has been in mic mode and boost
> is now high, I change it back to line... boost stays high. I have to use
> alsamixer to turn it off. This I think is a bug not a design problem.

This should not be a practical problem. If you record from Line, the 
current boost setting should not matter anyway.

Also, for Skype (which I saw in a later email): This is also probably 
not a PulseAudio problem. There is a checkbox in the preferences of 
Skype that controls whether Skype should automatically set the input 
gain in PulseAudio. Try unchecking it.

> Anyway, I personally think pulse is too buggy for input use.

I think PulseAudio is just fine for input use. We might need to fix your 
HDA Intel driver though. I can't promise to commit time to doing that 
right now, but it would be interesting to look at your alsa info ( 
https://wiki.ubuntu.com/Audio/AlsaInfo ) to know what chip it is that 
behaves in this unusual way.

David Henningsson, Canonical Ltd.

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