You have probably come across the term ISO track in audio as it has now become an industry standard for drama and other location sound work.
ISO is short for isolated. Isolated from all other audio signals. Now with better technology at the start of the 2000's audio recorders record a Left/Right, Aux and ISO's.
Each input used in the recorder can be recorded in ISOlation from after the gain stage but before the fader. This gives post production the ability to choose different sound sources other than a mix track.
A benefit of having ISO tracks are that they give you options.
If you have 2 actors talking to each other wearing lav mics and a boom op swinging over them, you have 3 inputs. Now if while the scene is going on there is an overlap in dialogue, you may find on playback that the radio mics give you enough separation to not need another take.
Staying with the same example, post production would get the following tracks to work on:
- L - Mix Track - R - Radio Mix - 1 - Boom - 2 - Actor 1 - 3 - Actor 2
This gives post production options to remix the different inputs/channels how they want, bearing in mind the ISO tracks are all clean and free from noise.
Options on location and in post are the main advantages of ISOs over just L/R mix tracks. Its always easier to delete than create. This doesn't compensate if you are not proficient in audio mixing or are trying to do everything yourself without a boom operator. Technology is never a substitute for lack of skills. Always hire a professional sound person based first of experience then equipment.
Important note about ISO tracks:
ISO tracks are not affected by the channel fader. They are only affected by channel gain, it is very important to have the right gain settings to deliver clean audio.