This is what the JX-03 manual says:
I'm kinda guessing that Sync1 and Sync2 are doing soft and hard sync, like as described here: https://en.wikipedia.org/wiki/Oscillator_sync. Although there are multiple types of soft sync. Is this right?SYNC 1–2
This is oscillator sync. It generates a complex waveform by forcibly resetting DCO-2 to
the beginning of its cycle in synchronization with the DCO-1 frequency. Setting the
value to 2 produces a greater effect.
MET 1–2 (METAL)
Produces a metallic sound by using the DCO-2 waveform to modulate the DCO-1
frequency. Setting the value to 2 produces a greater effect.
The Metal1 and Metal2 sound like some sort of FM synthesis?