Noam,
First, you should know that FCP7 doesn’t handle native AVCHD video well; everyone pretty much transcodes it using compressor, mpeg streamclip or a couple of other tools.
But the quick answer to your question is to pan the stereo clip center – putting both tracks (the one with audio and the empty track) panned center. Modify>Audio> Center Pan. Another way to handle this would be to modify the clip and tell it to no longer be a stereo pair. Modify> Stereo pair.
A stereo pair by definition is two audio channels. What you really want is to either remove the other audio channel (can be done on the timeline, IF it’s modified to be no longer a stereo pair.) When you do this you have two mono clips that both have pan and volume capabilities independent of each other.
Best,
Jeff G
Apple Master Trainer | Avid Cert. Instructor DS/MC | Adobe Cert. Instructor
————
You should follow me (filmgeek) on twitter. I promise to be nice.
New- my book (with Richard Harrington and Robbie Carman)- An Editor’s Guide to Adobe Premiere Pro
Compressor Essentials from Lynda.com
(older but still good) Marquee, Media Composer (3.5) and Basic/Advanced Color DVDs (1.0) from Vasst.com
Contact me through my Website