A pitch shifter effect moves the pitch of a recorded vocal up or down. Subtle pitch-shifting effects fix slightly out-of-key notes by nudging them into the correct pitch. This use of pitch-shifting is -- ideally -- invisible: the listener won't notice that the notes' pitches have changed. Shifting a note's pitch by more than a couple of musical semitones, on the other hand, creates a noticeable vocal effect. Moving a vocal's pitch significantly upward creates a helium-like or "chipmunk" effect, while shifting a vocal downward makes a vocal sound demonic or Darth Vader-like.
A vocoder effect uses a recorded vocal to modulate a synthesized sound. The vocoder takes the frequencies in the vocal -- the "modulator" -- and uses them to play the same frequencies in the synthesized sound -- the "carrier." Vocoders create a robotic vocal effect; the exact character of the effect varies depending on the type of synthesized sound wave that the vocoder uses. The Auto-Tune vocal effect also sounds like a vocoder; however, it alters the vocal by rapidly moving the pitch over a wide range rather than by modulating a carrier wave.
Double-tracking a vocal involves layering two separate recordings of the vocal track together. The slight difference between the two recordings creates a fuller, richer sound. A vocal doubler effect imitates this process by splitting one vocal track into two, then applying very slight delay and pitch effects to one of the split tracks. These effects can give music producers the richness of double-tracked vocals without the often tedious process of manually recording and layering the two different tracks.
Stutter and gate vocal effects rhythmically cut a vocal track in and out of the mix. A stutter effect repeats a short segment of the vocal several times; this process can either be automatic or manual. An automatic stutter repeats a defined portion of the vocal for a specified number of times, while a manual stutter effect involves cutting out a portion of the vocal's waveform, then pasting it several times in sequence. A gate effect brings the volume of the vocal up and down according to a defined rhythm. When the gate opens, the volume comes up; when the gate closes, the vocal stops playing.