The Pic'N'Mix Track
The Mix Track
A Mix track is used to give the picture editors a good start point to work with the visual and audio tracks without doing any dialogue editing.
The mix track is usually one or two tracks (L/R tracks) that is your mix of usually multiple sources and inputs. The 2 track/channel mix track will usually have Boom or several Boom mics panned to the Left (Track/Channel 1) and any wireless radio mics panned to the Right (Track/Channel 2). The video editor will then choose 1 of the 2 mixes and mute the other unless 1 becomes really poor as a reference for directors watching different video edits with sound.
Even on massive sound carts with more than 10 inputs, the mix track is still vital in terms of a guide reference to what the overall scene will sound like. This is again because the post production sound department will choose what they want from the ISO tracks.
A mix track on location sound will usually be sent to a set of cans for the director (via IFB or Wireless) so they can watch the monitor and hear the sound to better judge performances. Don't expect all directors to notice if a plane goes over during a take as they are focused only on the performances.
It's important to note:
The mix track unlike an ISO track is effected by the fader and the gain, you won't record a microphone source to the mix track unless the fader is up!
This is where ISO tracks can save you, or you can save the iso tracks from themselves.
Generally mix tracks are 'hotter' (louder on the meter) than iso tracks because of the combined signals and fader positions. Its useful to have a limiter on your mix track too so in dynamic scenes you can preserve audio quality.
Have fun Pic 'n' Mixing!