How to downmix 4 channels into 2

Or a quadraphonic record into a stereo one.

Le’s assume you have a bunch of files in one directory. The following script will downmix 4 channels into 2 with the following proportions:

  • LF => 100% LF
  • RF => 100% RF
  • LB => 100% LF
  • RB => 100% RF

and move the stereo files into a directory called “stereo”:

mkdir stereo
for file in $*
do
  sox -S -c4 "$file" -c2 stereo/"$file" mixer  1,1
done

If you want to change the front/back ratio to, for example:

  • LF => 100% LF
  • RF => 100% RF
  • LB => 70% LF
  • RB => 70% RF

the sox command will look like:

sox -S -c4 "$file" -c2 stereo/"$file" mixer  1,0.7

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