I don't remember what the gain is, but I think we set it a bit too high anyway. It was like 20 db or something. The data from the tracking circuitry goes directly into the tone generator modules. Sound Designer Rob Zantay helped me to design some cool sounds for it. Many of the sounds we created were dervied from factory sounds which we warmed up by turning down the modulation on some of the operators.
Operators are signal generators that can modulate each other in various configurations.
FM synthesis uses frequency modulation, whereas in the Casio PG380 phase modulation is used. You get similar sounds to FM, but a bit warmer in my opinion. In 1988 and 1989 I was an endorser for Casio because they had a line of instruments for professional musicians, and I liked what they were doing. The VZ technology was built in to the PG380 guitar, and you could exchange sounds between the keyboard or rack module and the guitar via memory cards. Also they had some quality samplers, the FZ10 and the FZ10M None of the products I am mentioning here are still being produced.