From: Jim Travers WBTV

I have had great luck recently using my DVCPRO D700 as an audio mixer while doing live shots.  Just have an engineer (or anyone who knows the secret handshake) go into the internal menu and set your audio output to the “mix” setting.  That sends both channel 1 and 2 to the audio out on the back of the camera.  Plug your audio cable into that jack.  This is a LINE OUT so you have to make sure you’re not plugged into a MIC IN on the live truck.

Then just plug your talent mic into your camera channel one and your second audio source into channel two.  Your audio controls on the side of the camera act as the mixer.  This works particularly well during elections when you have someone speaking at a podium behind a live shot.  You can just pot up their mic and pot down the reporters.  The added bonus is you can record every! ! thing off the podium because all the audio is running through the camera.