I currently have about 75 gig of music and close to 500gig of ripped movies and TV shows on my iTunes. I am now experiencing some slowness within iTunes. It takes about a minute to open iTunes (which doesn't bother me at all), but when I want to listen to a song I click on it and it take anywhere from 15-20 seconds for the song to play. I have noticed that if it's an AAC formatted song is usually plays instantly. So i'm wondering if I just convert my library to all AAC if that would do the trick. My question is will iTunes change the flies to AAC or makes a copy of the files in AAC format? Please help!