Dialogue nightmode downmix preset for 5.1 DTS to 2.0 AAC stereo using ffmpeg and qaac

[robertcollier4]

After converting many DTS movie tracks from 5.1 to 2.0 using eac3to, I have found the default eac3to channel mappings to result in very quiet dialogues and overly loud music and action scenes. Although the eac3to channel downmix coefficients have a scientific basis, they often do not sound good in practice bceause of low dialogue volume. This preset is for those looking for clear dialogues with left and right channel music still being audible but more in the background.

Requires: ffmpeg.exe and qaac.exe

ffmpeg.exe -report -loglevel verbose -i "videofile.mkv" -map 0:a:0 -f wav -acodec pcm_f32le -ac 2 -af pan=stereo:FL=FC+0.30*FL+0.30*BL:FR=FC+0.30*FR+0.30*BR - | qaac.exe --tvbr 127 --quality 2 --rate keep --ignorelength --no-delay - -o "audio-2ch-downmix.m4a"

The default eac3to channel matrix is:
FL' = 0.71*FC + FL + BL
FR' = 0.71*FC + FR + BR

This "nightmode" preset uses the following channel matrix:
FL' = FC + 0.30*FL + 0.30*BL
FR' = FC + 0.30*FR + 0.30*BR

As you can see - front center (dialogues) come in properly now and stay at the original level - while the music and explosions remain a background effect and don't overpower you. This preset solves the problem of you having to constantly fiddle with the volume knob when watching DTS 5.1 converted to 2.0 movies in order to hear dialogues. (Especially for watching movies in the night where you don't want to wake others but still want to be able to hear dialogues).

Try it out and you will notice a much better movie watching experience for 5.1 to 2.0 converted movies.