I listen to a lot of music on my 16gb iPhone 4 and I want to save some space. Most of my music is 320 kbps MP3's which some 256 kbps and 192 kbps. I currently have 1150 songs that take up 7.6gb of space. So how can I shrink the size of my music without a loss in sound quality? Which format do I use to save space and keep sound quality?