Bug 502057 - PulseAudio and ALSA volume misaligned
PulseAudio and ALSA volume misaligned
Product: Fedora
Classification: Fedora
Component: pulseaudio (Show other bugs)
i686 Linux
low Severity low
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Assigned To: Lennart Poettering
Fedora Extras Quality Assurance
Depends On:
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Reported: 2009-05-21 12:54 EDT by Oliver Clark
Modified: 2009-05-23 17:07 EDT (History)
4 users (show)

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Doc Type: Bug Fix
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Last Closed: 2009-05-23 17:07:58 EDT
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Attachments (Terms of Use)
alsa-info (19.70 KB, text/plain)
2009-05-21 12:55 EDT, Oliver Clark
no flags Details

  None (edit)
Description Oliver Clark 2009-05-21 12:54:45 EDT
Description of problem:
PulseAudio volume control and ALSA volume control not aligned.

Version-Release number of selected component (if applicable):
Name: pulseaudio
Arch: i586
Version: 0.9.15
Release: 11.fc11

How reproducible:
Always happens.

Steps to Reproduce:
1. Open ALSA mixer (alsamixer -c0) and PulseAudio's sound preferences or pavucontrol.
2. Reduce the volume using PulseAudio down to 0.
3. Watch the ALSA mixer get to -64 dB gain or 0% before PulseAudio.
Actual results:
Volumes from both ALSA mixer Master and the PA Output Device Internal Audio slider in pavucontrol:
PA 100, ALSA 100 (dB gain = -0)
PA 90, ALSA 88 (dB gain = -9)
PA 80, ALSA 72 (dB gain = -18)
PA 70, ALSA 58 (dB gain = -27)
PA 60, ALSA 45 (dB gain = -35)
PA 50, ALSA 30 (dB gain = -45)
PA 40, ALSA 17 (dB gain = -54)
PA 30, ALSA 2 (dB gain = -63) At this point there is 'almost no sound'
PA 20, ALSA 0 (dB gain = -64) 
PA 10, ALSA 0 (dB gain = -64)
PA 0, ALSA 0 (dB gain = -64)

Expected results:
PulseAudio and ALSA should both scale smoothly from -64 dB gain to 0.
Comment 1 Oliver Clark 2009-05-21 12:55:47 EDT
Created attachment 344991 [details]
Comment 2 Adam Williamson 2009-05-22 12:11:07 EDT
To be clear, here, the issue is really that when adjusting the volume with PA, you don't get a smooth scale from -64 to 0dB gain; the settings between 0 and 30% in PA are more or less useless.
Comment 3 Lennart Poettering 2009-05-23 17:07:58 EDT
PA 0.9.15 basically maps 0dB to 100% and -90dB to 0%. In between that the mapping from the 'percentages' to dB is 'linear'. At 16bit PCM resolution 'silence' is reached around -90dB. That's why the scale ends there.

Your sound card's schedule already ends at -64dB as it seems. To the effect that between -64dB and -90dB PA extends the attenuation range in software.

In the current git version of PA I changed the mapping between 'percentage' volumes and the gain. Now, the attenuation factor and the percentage have a cubic relation. This should give us a more 'natural' feeling of pixel distance on the screen and actual change in loudness.

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