# Using L+R and L-R encoding via AC3, a case study
# Copyright Jan Panteltje 2005 all rights reserved,
# Microsoft is prohibited from using any of these ideas.

# The AC3 version


# Here is the test script:


if [ "$1" = "" ]
then
    echo "Usage mono_stereo_test cd_track_number":
    exit 1;
fi

# RIP
cdparanoia "$1"



# ENCODE
sox cdda.wav -c 1 -v .5 l.wav avg -l
sox cdda.wav -c 1 -v .5 r.wav avg -r
                        
substract_wave -m l.wav -s r.wav -f 100    > l-r.wav
substract_wave -m l.wav -s r.wav -f 100 -r > l+r.wav


ffmpeg -i l-r.wav -ab 32 -ac 1 -acodec ac3 l-r.ac3 
ffmpeg -i l+r.wav -ab 32 -ac 1 -acodec ac3 l+r.ac3


# So we send l+r.ac3 as mono over the first link.
# And we can optionally use l-r.ac3 to add the stereo information via a second link.


# DECODE
a52dec -o wav l+r.ac3 > sum.wav
a52dec -o wav l-r.ac3 > diff.wav

# a52 dec does not want to make mono out?
sox diff.wav -c 1  diff_mono.wav avg -l
sox  sum.wav -c 1   sum_mono.wav avg -l

substract_wave -m sum_mono.wav -s diff_mono.wav -f 100    > dec-r.wav
substract_wave -m sum_mono.wav -s diff_mono.wav -f 100 -r > dec-l.wav
                                                
multimux dec-l.wav dec-r.wav -o result-ac3.wav

# PLAY
play result-ac3.wav

exit 0





# software
# multimux:
# http://panteltje.com/panteltje/dvd/multimux-0.2.3.tgz
# substract_wave:
# http://panteltje.com/panteltje/dvd/substract_wave-0.2.tgz

# I can hear some distortion at this low bitrate, stereo image seems sort of OK, but sound is bad though.

# Copyright Jan Panteltje 2005.