I'm the case of piano, the Realtracks are recorded on a Yamaha Disklavier piano, so the MIDI should be an exact representation of what was played (within the limitations I'd the Disklavier technology). Sensors in the piano detect what notes were played and the precise velocities.

For other instruments like Guitar, MIDI pickups are used. That technology is less precise, because it has to deduce what frets were played by analyzing the analog audio input coming from the string. Using that as a performance would depend on many things, such as what samples you are using in the MIDI synth, and the accuracy of the MIDI recording in the first place, and the importance of effects like vibrato that weren't captured.

So the short answer is that using the MiDI track from the Realtracks (ie the Realchart) as a musical performance works great for pianos and keyboards, and "hit and miss" for other instruments.

Have Fun!
Peter Gannon
PG Music Inc.