Many of us rely on Antares Auto-Tune for pitch correction on vocal tracks. It’s important to remember that it can be applied to lots of instruments too, for both pitch correction and creative use. Fretless bass, electric violin, trombone, even the Theremin, all feature continuous pitch potential, unconstrained by frets or keys. Here are some creative options using Auto-Tune:

Produce instant double tracking in one take
Record onto two tracks, processing only one of the tracks through Auto-Tune. If you’re going for a tight double track, set Retune Speed rather fast and Detune Auto-Tune slightly. Increase both of these parameters to broaden the doubled effect. You can also add some Vibrato to make a more dynamic effect (small depth and rate values are best, with medium delay). Of course, you can also record a single track and bounce that to another, processing through Auto-Tune. This way you can dial in the effect while auditioning the mix.

Record one source with two mics
Then use the Retune, Detune and Vibrato tactics described above. This can produce heterophonic effects (the effect of two players and instruments playing the “same” melody, with slight variations in pitch). The more constrained your scale is in Auto-Tune, the more variation there will be between the two performances.

Set up a drone or ambient aura behind a melodic performance
Try sending some of the vocal or instrumental melodic signal to Auto-Tune with an extremely constrained scale (for example, in the key of C: C, F, G, A#) and then apply a lush, long reverb to that track. The effect produced will be a steady backdrop of chanting tones behind the main melodic material.