stereo => mono

[toraneko]

I'm using LAME 3.93.1.

I use to encode audio files with "-m j -q 0 --abr" options so that their size equals the one of a CBR 128 bps file. this typically gives me something like "-m j -q 0 --abr 140".

I've read something like "joint stereo" stores "left-right" and "left+right" with different compression.

encoding an audio file into a mono MP3 file seems like to me as only storing "left+right" or maybe "(left+right)/2".

but it also seems that I can't divide by two the bitrate from "joint stereo" to "mono".

am I wrong ? which bitrate should I try to achieve ?

[killingspree]

hi,
iirc if you convert a stereo file to a mono you are doing some kind of a downmix from both the left and the right channel.

anyway, joint stereo means that only those parts of the left and right channel are stored seperately, which actually differ from each other. this way you actually do not have two full channels stored in the mp3 file. this allows you to save the space for those parts that actually differ, or let's you reduce the overall bitrate...

now, when you create a mono mp3 from a joint stereo one you of course have to store all the information once and only discard (reduce) the amount of space needed for those parts that were actually stored seperately first... this way you cannot simply reduce a 128 kbit stereo file to a 64 kbit mono file (i mean you can, but you'll have quite some quality loss), but rather have to go for a 96 kbit mono file...

hth
steVe

[toraneko]

ok. thanks for the explaination