Well, recently I found this article regarding how he changed his voice

To read the entire thing, go here:
http://www.steveperryonline.net/archive/news121698.html
"...As strange as it sounds, (the solo albums) were an attempt to change my voice," Perry explains. "I started listening to what the song called for instead of sing the same voice that came out of me on everything. I would just hope that the fans would appreciate my work and have the open minds to look into the solo side."
"...But there was other music in Perry's soul as well, and after Schon recorded two solo albums, the singer decided it was time for him to step out as well. So after the group's marathon 1983 tour, he started work on Street Talk. Perry says, he went after a live-sounding soul album. "If you listen to Street Talk, you'll notice there was a certain texture and guttural type of thing I did to my voice to try to achieve a different texture," he explains. Part of that was recording early in the day, when his voice was still "gruff." "

