#457: Pulseaudio's control of my LFE volume uses incorrect assumptions
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Reporter: mini | Owner: lennart
Type: defect | Status: reopened
Milestone: | Component: module-alsa-*
Resolution: | Keywords:
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Comment(by tschmelcher):
Continues to repro in Ubuntu Lucid here on my XPS M1710 too.
This is not a driver bug. I investigated the driver and hardware a lot and
discussed the issue with Raymond in my own ALSA bug report:
https://bugtrack.alsa-project.org/alsa-bug/view.php?id=5031 As you can see
in my last comment, I have requested that my "bug" report be closed,
because I decided that ALSA is working correctly.
The STAC 92xx chipset has two hardware volume controls, one for the L/R
channel and one for the subwoofer (LFE) that is derived from L+R. But
neither hardware volume affects the other. The so-called "Master" only
affects the stereo internal speakers. It has no effect on the LFE volume.
That's just how the chip is designed. :(
The job of ALSA kernel drivers is to present an interface to what the
hardware implements, so it is doing the right thing. AFAIK there is no
social contract in ALSA that a hardware volume control named "Master" is
multiplied with all others. If there were then it would be a design flaw,
because there is nothing to stop chipset developers from making a product
that is incompatible with that, as we are seeing here.
To fix this issue, PulseAudio needs to either change the LFE volume in
sync with the Master volume or use the PCM softvol exclusively, which is
the work-around that I have adopted by adding "load-module module-alsa-
sink control=PCM" to default.pa. The PCM approach is sub-optimal though
because a software volume presumably incurs quantization error at low
volume levels.
--
Ticket URL: <http://pulseaudio.org/ticket/457#comment:10>
PulseAudio <http://pulseaudio.org/>
The PulseAudio Sound Server
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