A detuner is an effects device that copies the original note, moves it slightly out of tune and then adds it back to the original note. The effect is similar to chorus, but closer to pitch shifter, as it doesn't move around or swirl like chorus does. This makes the effect more like a tracking effect – more transparent and not as wide as a chorus effect. It's ideal for thickening up a rhythm guitar track or making clean chords or arpeggios chime.
Detuners work by moving the note in percentage increments (-50 to +50 percent) and then offsetting them with very short delay times (usually from 0–60 milliseconds). Higher detune settings produce more dissonant sounds, and higher delay-time settings produce a short slapback (roomy) delay effect. Dual detuners enable you to combine two settings of detune together to achieve a wider image. With stereo detune, adding 30–60 milliseconds of delay to the detuner's voices that are panned to one side (while not delaying the other side) will change the detuner's stereo imaging greatly.
Detuners are more common as patches (programmable effects settings) in rack units, as they are a more modern take on the old choruses and tend to use the same circuitry as pitch shifters.