I already asked in the topic Tutorial 10-band vocoder (You are not allowed to view links.
Register or
Login) if it was possible to use the vocoder MFX without using external input as the carrier wave and we couldnt figure it out yet.
Still wanted to use the Vocoder on an AUX channel and after looking at the mixer block diagram of the MV it makes total sense

1. In the FX select the Vocoder, and set routing to AUX1.
2. Insert a nice vocal on an audio track, and route that to AUX1, but pan it all the way to the left.
3. Create an instrument (strings work well), and route that instrument to AUX1, but pan it all the way to the right. This will act as the carrier wave for the vocoder.
4. Enjoy
