Analog FM

[thefonz003]

I know that the vast majority of FM synths have been digital, and that due to the improved stability and precision this is considered ideal for FM synthesis. However, I was just wondering if there have been any widely-released true analogs that used FM synthesis beyond the relatively-simple 2-op version. Digital technology was still in its infancy in the mid-70s when the method was patented, so I'm sure analog FM happened at least once or twice. Did it produce any usable results? Are there commercially-released songs that use analog FM? I'm just curious.

[pflosi]

Lots of analog synths out there can do "FM". Beyond 2-OP though...? Hmmm... It's extremely easy in any sufficiently big modular, of course. The sound is completely different from the Yamaha style FM though (which, actually, is phase modulation, not frequency modulation). You might want to look into thru-zero oscs...

Apart from that though, what is "FM" anyways? If I frequency-modulate an oscillator with a 0.1hz LFO or an envelope, is that FM too? Certainly I'm modulating some frequency, no? When does it start to be FM? At 29hz? 31hz? 50hz? When I'm tracking the LFO?

[meatballfulton]

Since each operator requires an oscillator, an EG and an amp stage doing more than 2-op in analog requires more resources than any hardwired analog currently offers.

In a modular it's doable and in the modular world "through zero" VCOs have existed for quite some time. They cost a lot more than other VCOs, though. The VCOs must be super-stable and allow very accurate setting of the frequency because it's the ratios of the VCOs frequencies that are important in creating what we think of as classic FM timbres. The "organic" pitch drift so loved by analog fans is pure poison to FM. Stability and accuracy is not a problem in the digital domain though.

[marinedalek]

Not only frequency drift, but even altering the initial phase can substantially change the timbre of an FM sound. I can hear this effect on my DX7S if the pitch bend is gently tweaked and released on a sound with high modulation amounts - bending the pitch knocks the oscillators out of phase and causes a sustained tone to change in character.

You could get around that with a DCO of course, though you'll never get everyone to agree that that counts as "real" analogue, plus you then run into issues where the pitch of the oscillator is only updated at the start of each cycle, completely negating most of the effects of FM synthesis. A very cleverly-implemented DCO which allowed instantly-variable pitch (boy would that be interesting to design -.- ) might cut it, but that's as close as you're getting to DX7-style phase-accurate FM.

[cornutt]

Apart from that though, what is "FM" anyways? If I frequency-modulate an oscillator with a 0.1hz LFO or an envelope, is that FM too?

Yes, absolutely. Of course, the only audible effect is vibrato, but if you had a spectrum analyzer with enough resolution, you could see some tiny sidebands with 0.1 Hz spacing. At what modulation frequency you will start to "hear FM" depends on the shape of the modulating waveform and the index (amplitude of the modulating waveform), but generally you'll start to hear FM overtones when the modulation gets up around 25 Hz.