You can do your own blind testing. The nicest way is to download a computer-based ABX comparator. I forget the exact URL, but Google that phrase and you'll get it.
I suspect that the audibility would depend on your playback equipment and listening environment. Wouldn't be surprised if it's hard to hear a difference when listening through standard IPOD earbuds while working out at the gym. But I suspect the difference would be apparent on at least some music if you were playing it back through an audiophile system in your listening room.
I've done similar comparisons myself with CDs I've ripped using I-tunes. 320 Kbs sounded a bit better than 128 to me on some music when using the IPOD with Shure E3 headphones. The difference was much more dramatic when played back through my living room system. Seems like much of what gets lost through the compression is the soundstaging and ambience -- things that don't come across that great in headphones anyway.
I suspect that the audibility would depend on your playback equipment and listening environment. Wouldn't be surprised if it's hard to hear a difference when listening through standard IPOD earbuds while working out at the gym. But I suspect the difference would be apparent on at least some music if you were playing it back through an audiophile system in your listening room.
I've done similar comparisons myself with CDs I've ripped using I-tunes. 320 Kbs sounded a bit better than 128 to me on some music when using the IPOD with Shure E3 headphones. The difference was much more dramatic when played back through my living room system. Seems like much of what gets lost through the compression is the soundstaging and ambience -- things that don't come across that great in headphones anyway.