I was in musical ensembles throughout secondary school and college — marching and concert band, orchestra, choir. One of the most fun aspects of playing music in a big group was getting to know the inside of a piece. When I hear a piece on the radio or a recording, I notice the melody and the general melding of the sounds, but when I’m playing the same piece, I discover that nifty trombone melody or that cool rhythm in the lower strings that I wouldn’t otherwise notice.
Now that I have an MP3 player, I’m discovering that earphones give me some of the same effect, and not just with classical music: I never really noticed the bass lines for many favorite pop songs before; now I can hear and notice them, and realize why these folks are appreciated for being such good musicians.
It’s great to discover new aspects of songs I’ve known for 20+ years.