Indeed it is Masse Broberg on the first album and also most of Osculum Obscenum - there is a fairly easy distinction between the two (Masse and Peter).
Peter Tagtgren's vocals are pretty diverse considering the scene. He is pretty talented and seasoned.. he admits, when asked by an interviewer somewhere in an interview why each type of vocal from him sounded great and why he was successful. Peter said something like: "I have been around for a while" in response -- I always notice that Peter is always modest. Never boasts or puts on an act; he's always himself. And that's admirable.
For more of his gutteral growling/grunting:
-Inquire Within
-Apocalypse (moreso in a live version)
-Fourth Dimension
He is pretty impressive during 'Hypocrisy Destroys Wacken' days as well.
Plus, a few songs are mentioned in this thread. And I'm sure people could list more
Shrieking/Screech:
There's a good screech in a live version of 'Fire in the Sky'
A good screech in 'Fusion Programmed Minds' (one of my favorite tracks)
And in various Hypocrisy songs that we all know.
By the way, doesn't Peter sound reinvigorated for this new AToED album? Maybe its just me but the rest for the band seemed really good for him. He sounds great to me, moreso than normal. At a peak again.
Sorry for the long post. \m/