If you use Logic or Logic Express (which is what I am familiar with), music you play or compose is visible graphically if you wish.
You can lengthen or shorten each note, or grab a note and drag it up or down to change the tone, you can make it louder or softer. It is amazing what you can do.
I use a Mac and Ivory Piano (excellent software) connected to a Clavinova keyboard using my DT880's. The sound is incredible. When I have somebody else to listen, they remove the headphones to make sure the sound is not from the external speakers. It is that real!
Logic is somewhat similar to Garage Band, but better.
Does anybody else around here use similar software?