Katy claimed in an interview Ariana Grande had the presently best female voice in pop music, but you know one has to take some of Katy's statements with a pinch of salt when her enthusiasm clicks in, hahaha. I like her indeed, I'm glad I bought the album (Ariana's). That impressionist-video is hilarious, I never knew Ariana could be such a great comedian!
On Alanis Morisette's first album I can hear the resemblance. I think it possible that in her earlier days Katy might have employed Alanis' trademark technique of switching from chest to throat and back very distinctly; on videos of her performing early songs like Search Me, or Last Call, I find it even more prominent. I think it might be possible that Katy could have practised singing with Alanis on her mind, in her early days, although I don't want to make that into an assumption while I can't ask her, LOL And there's this feeling I get that now, at the time of Prism, Katy has perhaps more than ever 'found her own voice', and to me there's perhaps finally nobody really who sounds like her; to my hearing, Katy has just totally become Katy; since I've heard through all of Prism in one go for the first time that question was done for me really.