For quite a while I had this problem with low volume while listening music or watching a video. The default mixer controls of alsa only give you master and PCM, but even setting everything to 100% , the volume is still annoyingly low. For quite a while I suspected this was a software problem. For example VLC is able to boost the volume level at 140% …

A while ago I found an interesting post (that I can’t find anymore) on this subject. The author suggested to add this snippet to your ~/.asoundrc .

pcm.dmixout {
  type plug
  slave {
     pcm "dmix"
  }
}

pcm.!default {
      type plug
      slave.pcm "softvol"
  }

  pcm.softvol {
      type softvol
      slave {
          pcm "dmix"
      }
      control {
          name "Pre-Amp"
          card 0
      }
      min_dB -5.0
      max_dB 20.0
      resolution 6
  }

This will add a new control setting in your mixer controls, named “Pre-Amp” that will allow you to boost considerable the sound in same situations. I’ve noticed that with this new control, the sound can get a bit distorted. Anyhow, better then not hearing anything.