I don't want to see tacumso, the original poster's request, dismissed without something of an explanation.

Yes, MIDI is the way we do this now. Done right, with a good MIDI synth, it can sound quite good. However:

I think that having RealTracks play a melody might be technically possible but extremely difficult.

There is a MIDI standard and you can program how a MIDI note is to sound. No such standard exists, to my knowledge, for programming audio snippets. PG Music developed proprietary technology in 2008 to bring us RealTracks (and RealDrums). Yes, some are single instrument soloists, but they are not under our direct control as in playing exactly what we would write.

Imagine how difficult it would be to reproduce a single note. You must consider attack, decay, duration, volume, and timbre. And I'm probably forgetting something. All these can be programmed in MIDI. How would you do it in audio?

So, nothing wrong in asking for this, but I suspect if it were easy, PG Music would have already done it a decade ago.

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