No. Frequency Modulation is literally the first derivative of Phase Modulation: so for all intents and purposes they're the same thing. Nearly everyone uses PM -- especially Yamaha -- because it's rather easier to implement and doesn't present nasty challenges when doing self-modulation. Even Chowning's original paper on FM used PM. But everybody calls it FM because nobody ever heard of a PM Radio.
The GP is probably referring to the (false) urban legend that Phase Distortion, a technique developed by Casio, was meant to get around the FM patent. But PD has very little in common with FM (or PM) at all: the relationship largely begins and ends with the fact that they both operate on the phase of the sine wave. But PD is quite different, and its closest cousin is waveshaping. Indeed PD has its own patent.
I think it's a stretch to call it an urban legend. Casio was uninterested in licensing FM and developed a similar algorithm/approach. As far as I know Casio wasn't licensing FM throughout the 80s but still wanted to be competitive in the digital age.
This happened in the wake of the DX7, which was a massive success. Casio's CZ line never really touched it but they had some interesting qualities to them. I had the 101 which I bought for ~ $70 when nobody wanted them and they sell for a lot more now.
I disagree. It's true that Casio developed its own digital synthesis approach as it couldn't do FM. But this was true of Kawai (additive, hybrid single cycle, then PCM), Ensoniq (hybrid single cycle), Roland (single cycle + PCM), Korg (PCM), PPG (wavetables) etc. They all "worked around" the patent but none of these methods were anything like FM. PD in particular was designed to simulate low pass and resonant filters on traditional waves in a clever and cheap way. This really was a far cry from FM. It was inverse waveshaping with a window. It IS true that Casio eventually gave up and moved towards FM in later models (VZ).
I think we're saying the same thing. I wasn't suggesting any of these approaches offered some loophole that replicated FM, but that these manufacturers decided there's enough synthesis techniques that come close in sound that they opted to do so rather than pay Yamaha, as some other manufacturers did at the time.
Even if the underlying algorithms are nothing like FM if you get similar sounds (the gritty, busy waveforms) it made a lot of sense to market it and dilute the appeal of "FM" as THE digital synthesis method of the 1980s, as the DX7 nearly did.
I also wouldn't loop in wavetables with these approaches.
