Auto Tune is an audio processing technology originally created by a company called Antares Audio Technologies. It is designed to measure and alter pitch in vocal and instrumental music recordings and performances.
Originally designed to disguise off-key notes by shifting their pitch to the nearest true semitone, it has also been used to effectively distort the human voice by raising or lowering pitch significantly, so that the voice is heard to instantly change from note to note like a synthesiser.
The first commercial use of Auto Tune as a vocal effect was in Cher’s “Believe” in 1998. The producers of this song originally claimed that they had used a DigiTech Talker FX pedal in the song, however Cher’s producers discovered that they could “exaggerate the artificiality of abrupt pitch correction” with Auto Tune, creating an technique that became widespread in use during the first ten years of the 21st century on tracks such as Daft Punk’s “One More Time” amongst others.
Auto Tune is used by a number of artists for live performances in it’s originally intended mode (where it is designed to be mostly undetectable) to ensure that they deliver on-key notes, however the likes of Christina Aguilera and Death Cab for Cutie have taken a public stand against using Auto Tune in their live performances.