[sdiy] Synergy FM [was: Re: DX7 hacking?]

Lanterman, Aaron lanterma at ece.gatech.edu
Sun Jul 1 23:36:15 CEST 2012

On Jun 30, 2012, at 3:27 PM, Barry Klein wrote:

> I was more wondering about the engine hacking. 

As an aside, the Digital Keyboards Synergy is actually a fairly powerful FM synthesizer. I guess that to avoid legal issues with Yamaha, they downplayed this (calling it "phase modulation" instead of "frequency modulation" -- but in many cases they're equivalent, and the DX series is really a PM implementation of the FM idea anyway), so a lot of folks don't know about it (and of course DX series synths outsold the Synergy by a factor of zillions-to-one or thereabouts.)

A Synergy voice has these little flags that you can set for each oscillator that determines whether it gets added to an accumulator (the "additive" aspect) or modulates the next oscillator. By twiddling these I suspect you could implement most of the DX algorithms, except for the ones with feedback (I can't recall or now if there's a way to implement feedback on the Synergy -- there might be on that I'm forgetting). It's been a while since I looked at it, though.

The Synergy is limited to 32 oscillators, so doing something like 6-op FM would drop you down to 5 voice polyphony (etc. etc.), but that's pretty good, actually.

Envelope scaling of oscillators on the Synergy is performed using a phasor-addition trick, so the phase relationships between the oscillators are always sliding around. This probably has an effect on the character of its FM relative to the Yamaha synths. 

I'm not sure how many of the Synergy library voices exploit this FM capability. A quick tour through the presets shows that at least a few do -- there are some with dense spectra that are (a) characteristic of FM-type sounds and (b) thins that you couldn't pull off additively with so oscillators. Some of the FM-ish tones, though, like xylophones or bells, that would be done with FM on a Yamaha, are probably just straight up additive on the Synergy (facilitated by really flexible frequency envelopes.)

Once you add the Synergy's pretty sophisticated envelopes, you have a really interesting machine that could give the DX series a run for its money -- that is, if Yamaha hadn't been able to get the price point as low as they did! If Digital Keyboards had access to ASIC design and fabrication facilities, history might have been different.

- Aaron

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