The V256 has two optional internal synthesizers so that you don’t need to have an instrument plugged in to start vocoding. The three Robo sounds (which are all identical) have a synth that makes you sound like a robot. The drone modes have a synth that is more like an organ.

Single Drone is one note, Major drone is a major triad or chord and Minor drone is a minor triad or chord. Turning the Pitch knob in all 6 vocoder modes will set the pitch of the internal synth. Turning this knob fully CCW clockwise will turn off the internal synth so you can use external instruments. You can also use MIDI to control the internal synths.

The bottom three modes are all pitch shifters.

Reflex Tune is automatic pitch correction based on the scale you set it to or the chord you play on your instrument.

Transposition is simply pitch shifting your vocals by a fixed amount, +/- 1 octave.

Instrument Control mode allows you to pitch shift your vocals to whatever pitch your instrument is playing. It is a monophonic effect. Play an E note on your guitar, no matter what note you sing into the effect it will output the same E note your guitar is playing.