Has anyone figured this one out?

When the audio is not 48k, you can transcode it -- and you can either choose a specific bitrate to use, or you can choose "optimal". But this is not explained in the help or anywhere else.

I wanted to believe that "optimal" meant "the same bitrate as the source", but this doesn't seem to be the case.

I just used Audio Transcode with the "optimal" setting, and the transcoded audio was smaller than the original! This is really lousy, since I picked the source files so they would exactly fill a DVD!

So how does DVD-Lab determine "optimal" audio bitrate?