Where are my music files?

Today I created an additional Music Library to accommodate another iPod Touch 4G by following the instruction posted here: http://support.apple.com/kb/ht1495

Neither the original Library, nor the new Library have altered in size or content, but my iMac has seen its hard drive drop by 7 or 8 Gbytes of storage capacity. Obviously the data is on the drive, but I'm not able to locate it.

With much of the data in Mountain Lion hidden from view (like the User Library) I'm finding it very difficult managing files.

Does anyone know where the music files I can't seem to locate might be stored?