Channel downmixing in MPlayer

Recently I have been playing with downmixing in MPlayer.  When I bought new speakers, I decided to go with stereo instead of surround since I mostly listen to music. As anyone using mplayer or any “derived” players such as vlc have discovered, there is a incredible annoying problem that the voices of the actors are very low, actually in general the sound is very low. It appears that when mixing to two speakers, the center channels is put very low in the mix. The same could be said about the subwoofer although it’s naturally not as easily recognized.

A quick google revealed that MPlayer has several tricks (audio filters) that might potentially work: volume, volnorm, pan, hrtf. I quickly discarded volume and volnorm since I don’t want to just boost the sound, I want it to distribute the channels properly. hrtf seemed like a good simple choice, since pan looked very complex. Sadly in the middle of Harry Potter I had to turn it off because it was making lots of clipping of the sound. So I was left with pan. It took a while to get a good default, but a bit of googling around revealed one with a decent default. I first just tried turning sub + center up to one but in one or the other movie introduced the dreaded clipping. So I had to keep it down a bit while still retaining decent boost of center and sub. After an afternoon of testing I came to the following “magic” formula:

-channels 6 -af pan=2:0.4:0:0:0.4:0.2:0:0:0.2:0.3:0.3:0.1:0.1

Please do note that one needs to add a -channels 6 in order for mplayer to decode all 6 channels so that it can mix it down to two. One can read more about the pan filter here.

5 thoughts on “Channel downmixing in MPlayer”

  1. Interesting, though the option doesn’t work well with my video. The voices of my video are still heard only in the left speaker, but the other sounds are slightly appended to the both speakers, I guess. As a result, I feel more “surround” sound.

  2. Hmm very strange with the left channel thing barosel. You can tweak the parameters so that the right channel is boosted more. If it’s voices, then it should be enough to just tweak the center channel. Glad it works for you with the surround effect 🙂 I guess that is also what it’s supposed to do.

  3. Thank you so much for this blog post. After downmixing DTS I had no center channel at all, but this makes everything sound great!

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