On 10/11/2012 10:36 AM, Doug Pomeroy wrote:
> A carefully made mono mix (L and R exactly equal) will
> cancel that part of the the vertical component which is the
> same in both channels.

A good way to accomplish this:

1. Highlight a representative section of audio and zoom in on it.

2. Reverse the polarity of ONE channel only.

3. Set up a mono mix and adjust (in preview mode) for MINIMUM signal. By 
ear is usually best; you want as little of the desired audio to be 
audible as possible. Ideally, you just hear noise.

4. Write down your settings, then undo the polarity reversal from Step 2.

5. Using the settings you wrote down, mix the whole piece down to mono.