"Joe Kesselman" wrote in message
...
How have you specified the MP3 compression? If it's bits per second, a
mono version *will* be identical in size to the stereo version.

Also, I believe MP3 uses a mid/side representation, since (as in FM
stereo) you can assume that most of the information is actually in the mid
so side can be compressed more agressively. If so, a mono signal encoded
as a stereo MP3 is all mid, no side -- and the genuinely mono MP3, again,
would be essentially the same data.

So that's two possible explanations for your observation.

I think that the Apple iTunes encoder refers to this as "Joint Stereo"
encoding. If I understand correctly how it works, the encoder optimizes the
file size whenever it can by looking for the mono component of the file.

dave