I believe he uses a computer program called Anatares Auto-tune... I also believe that KiKi Sheard uses the same thing... I have the program in my studio... If you know anything about computer recording (Pro Tools, Logic, Cubase, Cakewalk, etc.)... the program runs as a plugin vocal effect that automatically corrects any off notes in real-time (while the song is playing) based on a user-specified musical scale, if the rate of correction (in other words the speed/frequency in which the pitch corrector responds to an out of tune note) is set to a very fast speed it creates an unnatural, "robotic" type sound. When the effect is applied to each vocal track it creates a perfectly in tune harmony... If used on a solo vocal track... It creates an effect similar to R&B artist T-Pain.