Roland AIRA Compact E-4 Voice Tweaker - Manual (Page 17)

Using a Vocoder Voice to Alter the Sound (VOCODER)
17
Adding a chord (HARMONY)
1. Press the [HARMONY] button.
You can press the [HARMONY] button to add more carrier voices.
You can also set the pitch of the carrier.
Setting the carrier to a fixed pitch
Ø Correcting the Pitch (AUTO PITCH) (P.8)
Setting the chord type
Ø HARMONY_TYPE (P.14)
Setting the chord key and scale
Ø KEY_SCALE (P.13)