Difference between audio and MIDI...
Audio: This records actual sound from a microphone or other line source. This is actual sound being recorded like you hear on a CD or tape.
MIDI: This records the MIDI output from a MIDI controller (which often are keyboards, electronic drums sets, wind controllers, MIDI guitar conrollers, etc.) MIDI has no sound. It is only the recording of events which trigger sounds. So you record the MIDI and then use the MIDI track to trigger synthesizers, sound modules, software synths, etc. You can then in turn record the output of the synths as audio tracks. Why mess with MIDI you ask, flexibility. You can record the MIDI and then have it trigger a piano sound. If you don't like the piano sound, have it trigger an organ or string sound etc. Or for me, I have no piano nor the space to record it in. I record a MIDI track fro my MIDI keybaord and then I have probably 30 or so piano sounds that I will flip through to find the one that works the best for the particular piece at hand. YOu don't want to record a school upright piano for an orchestral piece. THis way I can use any piano I want.
BTW, for more help with n-track stop over at
www.ntrack.com or
www.audiominds.com and check out the forums. There are probably 20x more ntrack users over there to answer questions for you then on HomeRec.