Songs with a lot of bass, high pitched vocals, and listening with expensive headphones, you'll hear the difference. It sounds so crisp if you have the m4a format
I have Pro Beats by Dr Dre and even HQ and 320kbps sound different. They are AMAZING! I recommend getting beats, there are other cheaper kinds. They've made me enjoy a lot more music because you can actually hear the production, and they also let me know when something is really bad.
It's also may have something to with how big a file is. A lot of my files may be between 128 to 192kbps, but the file size ranges from 6 MB to 11 MB, sometimes even more.
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I just discovered that some of my favorite songs on iTunes are 128kbps.
