Hello, I have a sound file in .m4a format. For strange reason, whenever I click on it under iTunes, some other music are played. I opened it using QuickTime. The playback is sluggish. For example, I clicked on the middle of the time line, it take about 8 seconds to play back. Is there any good app (preferably free) that allows me to do sound editing such as saving portions of the large sound file into separate smaller files? Thanks.