Also called Direct Note Access.
This new technology permits the dream of every recorded musician — to be able to change one note in a chord or polyphonic recording. Just that one note! Either change its pitch, timing, key, duration. Now you can. This software Pro Tools plugin from Melodyne will unravel polyphonic recordings (not mere MIDI) into its composite notes and then allow you to alter their characteristics via an visual interface.
Even if you are not a musician, you can appreciate the power this new tool offers, as shown in this instructional video.