I'm looking for bands with vocalists that scream as hard as they can, it's really that simple. I'm getting back into death metal and black metal and I need some really strong shit.

In my opinion Frank Mullen is the quintessential ferocious death metal vocalist. Martin Van Drunen and Steeve Hurdle (Only Gorguts' Obscura album) are pretty insane-sounding as well. In black metal, Varg sounds pretty tortured on some of his earlier material (Check out the song Det Som En Gang Var). V.I.T.R.I.O.L. from Anaal Nathrakh is also another good choice.

Edit: I should say that Frank Mullen is from Suffocation and Martin Van Drunen is from Pestilence (First two albums), Asphyx (First two and last two albums), and Hail of Bullets.

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Simple enough to ask in the help thread, use the rec forum for these kind of requests.