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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.)


UPDATE

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.

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    Back in the day on Synth Secrets, web.archive.org/web/20160404062919/http://www.soundonsound.com/…, Reid claimed that "cross modulation" always refers to frequency modulation. I don't know the difference between linear and exponential FM, and don't know which osc is modulator and which is carrier however. – Pat Muchmore May 7 '17 at 12:38
  • @PatMuchmore Thanks for that link. I have found a few other mentions on forums suggesting it is exponential FM going from oscillator-2 to oscillator-1, and that it changes the pitch of oscillator-1 (which makes sense). Maybe the "cross" simply means from one oscillator to the other, and doesn't imply that the modulation works both ways. – Your Uncle Bob May 8 '17 at 0:51
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The characteristic feature of cross modulation is that the two signals have similar frequencies, both in the audio range. That creates quite a different effect from amplitude or frequency modulation driven by a low frequency oscillator (i.e. with a frequency between say 5 Hz and maybe as low as 0.01 Hz) where you can hear the effect of each individual cycles of the LFO, or slow changes in the sound of a drone.)

Probably the nearest equivalent to cross modulation would be ring modulation as in early analog synths, or "FM synthesis" as marketed by Yamaha in the 1980s, for example in their DX7 synth.

The frequency and amplitude content of the cross-modulated signal doesn't necessarily have any simple relation to the two inputs, and what you hear doesn't necessarily have a simple relation to what you would measure with a frequency spectrum analyser either, since your ears and brain are a highly nonlinear signal processing system! You could describe it as a "there are no rules - just play with it till you get something you like" type of effect!

  • Thank you for answering. I'm creating a Roland-inspired virtual instrument, but unfortunately have only Juno synths to compare with, and therefor I'd like to find out the exact details of the cross-modulation implementation: AM or linFM or expFM or phase modulation, using which waveforms, in which direction, at what level, etc... – Your Uncle Bob May 7 '17 at 1:08
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    It's a fine answer, but it's not really an answer to the question posed. – Bruce Fields May 8 '17 at 17:44
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One would think that the 'metal' choice on the JX3P refers to Ring Modulation (RM). The reason for my thinking so is that the option was often used for bell like sounds, which is also typically associated with RM. I don't know this for a fact, of course, but it seems to reason.

Just the name brings back memories of making some of the coolest bells and S&H sounds, and I am very much partial to metallic timbres. Also, I recall it had Frequency Modulation (FM) which sort of infers a separation between FM and CM (in terms of Roland's use). Sadly I do not have the synthesizer anymore.

This does not answer your question anywhere near 'exactly', but I think you would need someone from Roland in order to find that kind of answer.

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