Where are my mp3 versions of my iTunes music?

I purchased songs from iTunes and I also copied my CDs into my iTunes library. I have figured out how to encode this music into MP3 format for my Coby mp3 player. However, I don't know where the encoded mp3 versions of my songs are located on my MacBook. I can see that the song is being encoded, and the left hand column with all my playlists moves, but I don't know where to find the new mp3 version. Please help. thanks.