I'm not sure I fully understand the question, but...
...if you are asking "is it possible to separate one instrument from an audio recording
where it is mixed with other sounds/instruments playing at the same time?" the simple
answer is "no". Many liken this to trying to make a cow back out of a box of beefburgers
(or maybe a horse nowadays...)
...if you are asking "is it possible to edit sections of audio where the single
instrument I want to hear is playing on its own?" the answer is "yes". All you need is a
simple audio editing package and you can chop the file up into as many sections as you
If you can get a MIDI file of the piece you are working on then it's
job done - pop this into a typical DAW (Cubase does it, if you know anyone with a copy)
and it will display the score.
Hope this helps - or please correct my
understanding of your question!
An Eagle for an Emperor, A Kestrel for a Knave.