I think the best way to get more realistic sounding midi is to think about velocity, volume and timing and the musicians trying to perform the part. When it comes to velocity a lot of people tend to leave the notes as entered which are often all the same velocity which is far from the truth. Most guitarists hit different notes harder or softer. A lot of folk use velocity for volume control which might not be what you are looking for. How velocity behaves has a lot to do with realism. Some synths use velocity to change the envelop of the sound once again to enhance realism. The other is timing, people use quantise to make the track spot on with timing once again very unrealistic. I don't know of any guitarist for example that plays exactly on time (nor do they want to) understanding how a guitarist might feel has a lot to do with getting a more realistic sound. For example in an exciting part the guitarist might be slightly ahead then back to a layback part be slightly behind and sometimes spot on.

There is a lot to getting it right but understanding the players part has a great deal to do with getting more realistic midi. With wind instruments understanding the player needs to breathe is vital. Most wind instrument players cannot go through a 3 minute tune without a breath yet I have heard midi parts that have a continuous stream of notes (not realistic). Once again velocity is vital when doing wind instruments. This could go on and on but the key is understanding what the player would do has a lot to do with creating good midi files.

My thoughts

Tony

HP i7-4770 16GB 1TB SSD, Win 10 Home,
Focusrite 2i2 3rd Gen, Launchkey 61, Maton CW80, Telecaster, Ovation Elite TX, Yamaha Pacifica 612
BB 2022(912) RB 2022(2), CakeWalk, Reaper 6, Audacity, Melodyne 5 Editor, Izotope Music Production Suite 4.1