I've always been told that the Shure SM57 and SM58 are essentially the same mic with different grills, and that they sounds indistinguishable. I know that people use both of them for micing up amp cabs and vocals. But I have one of each (I've had many of both over the years), and I sear that the SM57 is crisper, less muddy, and more harsh than the SM58, specifically when used on vocals. It doesn't matter if I have a foam pop filter on the SM57 or not, it sounds very different than the 58 either way. I almost prefer the 57 for vocals, but it depends. Has anyone else noticed this, or am I imagining it?