Lets say I use a computer to change my voices pitch, or use computer generated voices to hit a repeater. Is this allowed, or does it have to be my natural voice coming in on phone transmissions?
I am in the United States of America.
Nowhere in FCC Part 97 does it specify you have to use your natural voice. And, as many commenters have noted, there are lots of places where you don't. I will add to that list:
The key is that the control operator is identified in accordance with FCC rules and since that licensee's identity is clearly known from the ULS database, there's no attempt to really hide from anyone who cares enough to look you up.