I've had a mildly annoying problem with my sound for quite awhile now, and I've finally decided it's time to do something about it.
Every time I adjust the main volume slider in the toolbar, or use my volume hotkeys on my laptop, Ubuntu adjusts my mixer levels in a strange way. When I open GNOME ALSA Mixer, I notice that there are three output sliders for my SigmaTel STAC9200: Master, PCM, and LFE. Master and LFE both have Mute checkboxes.
When I press my volume up hotkey once, Master and LFE unmute, and the sliders for PCM and LFE jump up about halfway. The Master slider stays at zero. Another press brings PCM and LFE up to about 4/5, and Master remains unmoved at the bottom.
Ubuntu doesn't move Master until PCM and LFE are maxed out, which occurs between about 15%-20% on the main output mixer.
The effect of this is that I don't get any sound at all until about 15%-20% (since Master is at zero), and when I cross that threshold, I immediately get a loud bassy sound (from the LFE apparently). If I use headphones, I still don't get any sound until that threshold, but at least it doesn't blast me when I do get sound.
Is there anything in PulseAudio configuration or anywhere else that could change the behavior of my output mixer?
There are many layers in the audio stack that could contribute to this symptom. Most directly is the behavior that PulseAudio defaults to, and you can read about that at http://pulseaudio.org/wiki/PulseAudioStoleMyVolumes. You can work around some instances using the instructions I contributed at https://wiki.ubuntu.com/DebuggingSoundProblems/KarmicCaveats#Volume%20range%20anomalies:
Finally, whether this anomaly is actually a bug requires you to use