DigiTech Midi Vocalist

Studio Sound say :

The Digitech MIDI Vocalist is an intelligent pitch‑shifter. This means that it 'understands' the rules of harmony and can add harmonies to a lead vocal that are appropriate to the key of the song. (Brian May soundalikes may substitute 'guitar' for 'vocal' in the previous sentence, because the unit is not restricted to vocal processing.) Being intelligent and bestowed with a certain amount of good taste, this is not a unit for creating weird, delayed feedback pitch‑shift effects, although you can certainly construct such sounds with the aid of a delay unit and a little bit of mixing console know‑how.