How does Chuck Schuldiner change his voice so much?

First, there is his ';Scream Bloody Gore'; growly scream, and then ';The Sound of Perseverance'; high pitched shrieks. Especially in the Painkiller cover...



And his normal voice you hear on interviews is even more different...

How can you be able to change your voice so much without affecting it?How does Chuck Schuldiner change his voice so much?
His naturally progressed that way. If you look at the later live videos, He could not do the deeper growls that he did in the past.





Pull The Plug (studio)

http://www.youtube.com/watch?v=wm9pNmBFZ

Pull the plug (1988)

http://www.youtube.com/watch?v=bgK60w0yH

Pull The Plug (1998)

http://www.youtube.com/watch?v=5-WyzxJUg



I really dislike the higher voice, just doesn't sound right to meHow does Chuck Schuldiner change his voice so much?
lots of people can change their voice a lot



i.e http://www.youtube.com/watch?v=w1X4wrlbS



http://www.youtube.com/watch?v=DuGpHsxb7



or http://www.youtube.com/watch?v=bCMC_Ag9I
Like all Chucks (see: Norris), he's awesome.
i'm sure some of it was just over time.