Roland's later analog synthesizers have a setting for cross-modulation between the two oscillators. I'm trying to find out what the exact technical nature of this effect is. Is it phase modulation, linear frequency modulation, exponential frequency modulation, amplitude/ring modulation, or something else entirely? And does it go one way, or does it affect both oscillators, as is suggested by the term "cross-modulation"?
On the Jupiter-6, there are two faders in the oscillator-1 section to set the cross-modulation level manually and to have it influenced by envelope-1.
On the Jupiter-8, there is one fader in the oscillator-1 section to set the cross-modulation level manually, and it is indicated on the panel as a signal coming from oscillator-2.
On the JX-8P and JX-10, there is a switch in the oscillator-2 section to set the cross-modulation level from 0 to 3.
(On the JX-3P, there is a switch in the oscillator-2 section with settings "off", "sync" and "metal", but nothing to set the cross-modulation level. It looks as if the cross-modulation on the JX-3P is very different from the implementation on other models.)
A few (vague) sources on internet forums suggest that the cross-modulation is exponential frequency modulation of oscillator-1 by oscillator-2.
I'd be interested to have this confirmed by someone who has access to a Jupiter, and ideally I'd like to know by what interval the pitch of oscillator-1 goes up and down when oscillator-2 is set to a square wave and low-fequency mode, and the cross-modulation level is set to maximum.
Further Googling suggests that on the JX-8P and the JX-10, the four settings are 0: off, 1: oscillator sync (oscillator 2 synced to oscillator 1), 2: cross modulation (apparently oscillator 1 modulating the frequency of oscillator 2) and 3: oscillator sync combined with cross modulation.
So the cross modulation on the JX synthesizers seems to go in the same direction as the oscillator sync (oscillator 1 controls oscillator 2), unlike the Jupiter-8. The Jupiter-6 could do oscillator sync in both directions, so there you had the choice of both options.