[pulseaudio-discuss] Couple of PA problems

Sean McNamara smcnam at gmail.com
Sat Nov 27 03:02:51 PST 2010


On Sat, Nov 27, 2010 at 5:24 AM, James Harkins <jamshark70 at gmail.com> wrote:
> THIRD time trying to post this...
> I'm having a couple of problems with pulseaudio. I can't find answers on the web and it's driving me perfectly batty.
> 1. When I boot into Ubuntu 10.04, the signal from the built-in hardware input is routed out to the built-in hardware output. That is, if I turn up the speakers and rub the microphone, I can hear the sound coming out of the speakers. By contrast, if I boot into Windows, the sound is not so routed.
> This is an irritant for normal use, but I also plan to perform live electronic music using Ubuntu. If sound from the laptop's built-in microphone pollutes the output audio stream, that's completely unacceptable. (OTOH, Jack suspends PA and this might stop the unwanted routing. I hope... I don't remember exactly, will check later.)

Is this a default install of Ubuntu 10.04 with no modifications at
all? It might be worth filing a bug on Launchpad. The main thing they
need to know is the exact make/model of your laptop, and the exact
audio chipset. Since audio configuration is so needlessly variable
across different PCs -- especially laptops -- the level of detail
needed is excruciating. To save you some confusion, the easiest way to
gather a comprehensive description of your audio hardware is with
`also-info.sh'. Download and run this script; it has built-in usage
instructions: http://git.alsa-project.org/?p=alsa-driver.git;a=blob_plain;f=utils/alsa-info.sh

There is virtually no likelihood of this feedback routing being at the
PulseAudio layer in a stock Ubuntu configuration, but you can examine
your source/sink settings using gnome-volume-control-applet
(installed/enabled by default in GNOME-based Ubuntu), or with
pavucontrol, which is an older utility that some like better.

That said, I had a laptop one time where the internal speaker and the
internal mic were virtually right next to one another beneath the
keyboard, and the default ALSA settings wrongly set the capture
monitor (a playback channel that plays back sound captured with the
mic, through the speakers) as enabled by default. This would cause a
very loud feedback loop as soon as ALSA's mixing controls were
initialized. You may have a similar situation, where ALSA doesn't set
sane defaults for volumes, and PA isn't modifying the volumes either
(although I thought PA with flat-volumes enabled *would* modify them?

> I haven't been able to find any way to break the connection. There is no client application that sends in --> out. It's either pulseaudio or alsa, and the source of the connection is invisible in all configuration tools.
> This is very seriously frustrating for me. Any hints would help.
> 2. As a workaround for problem #1, I thought I could turn down the main system volume and then turn up the volume in client applications. But I found, for instance, that changing the system volume also changes the volume in rhythm box and vice versa.
> Why are these not independent? Where is the preference so that I can make them independent?

Why they are not independent: Good question ;-) The answer is that
PA's flat-volumes feature is enabled by default. Don't like it? Join
the club! But the PA devs believe that overall, most users will
appreciate the flat volume experience more than without. And, they've
made many refinements over the years to try and fix it. Some users are
happy with flat-volumes, and others aren't. Rather than drag out the
"validity of flat-volumes" debate again, I say, just disable it if you
dislike it, and move on with life. Maybe one day flat-volumes will
improve to the point that it doesn't randomly blast your ears out, and
then we can all enable it again ;)

Where is the preference: In /etc/pulse/daemon.conf, the flat-volumes
flag is commented out and the default (if uncommented) is yes.
Uncomment and set it to no, and restart PA, and you'll be good to go.


> Thanks.
> James
> --
> James Harkins /// dewdrop world
> jamshark70 at dewdrop-world.net
> http://www.dewdrop-world.net
> "Come said the Muse,
> Sing me a song no poet has yet chanted,
> Sing me the universal."  -- Whitman
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