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Old 25th March 2013, 17:38   #12216  |  Link
robertcollier4
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Join Date: Nov 2012
Posts: 30
I frequently downmix DTS 5.1 audio to 2.0 stereo for playing on my hardware player using "eac3to -downStereo" or "eac3to -downDpl". However with both I frequently have the problem (with DTS sources specifically) that explosions and sound effects are super loud and the dialogue are too quiet. What I want to do is basically "boost" Center channel.

The current co-efficients being used by -downStereo are:
FL' = FL + 0.7071 x FC + BL
FR' = FR + 0.7071 x FC + BR

What I want is something like:
FL' = FL + 0.85 x FC + BL
FR' = FR + 0.85 x FC + BR

Can I somehow use custom co-efficients with eac3to? or what tool can I use to convert DTS to WAV with custom co-efficients? Thanks. I am using Windows and would prefer a command line utility.

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UPDATE: I have found custom channel mixing from DTS can be done with ffmpeg.exe. For tracks in which eac3to downmixing coefficients result in too quiet dialogue, I have done extensive testing and found that mixing 0.25 coefficient Left and Right channels with 1 coefficient Center channels gives the best results for me for watching a DTS movie on a stereo system. Analytically this may seem like a very low amount of FL and FR - but it emphasizes crisp clear Center channel dialogues along with music which "accompanies" the movie instead of overpowering it.

This command will convert the first audio track in an mkv file into a stereo downmixed AAC M4A file. It will do the conversion in 32-bit float mode which is what libdts uses internally and so will avoid dithering before passing to AAC compressor. You need to have ffmpeg.exe and qaac.exe on your path.
Quote:
ffmpeg.exe -report -loglevel verbose -i "moviename.mkv" -map 0:a:0 -f wav -acodec pcm_f32le -ac 2 -af pan=stereo:FL=0.25*FL+FC:FR=0.25*FR+FC - | qaac.exe --tvbr 127 --quality 2 --rate keep --ignorelength --no-delay - -o "moviename-audio-dialoguedownmix.m4a"
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Last edited by robertcollier4; 5th April 2013 at 11:31. Reason: Answered own question
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