DX7 and all other Yamaha "FM" synths actually use phase modulation for various reasons including vastly improved pitch stability, not to mention computational ease. The AN1x probably does too, though it clouds the workings by reducing them to a few, differently named parameters. There might be other differences to suit the 'analogueness' of the AN1x if it's trying to emulate the FM in prior analogue synths rather than the DX.
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Re: fm
2016-01-26 by Daniel Boles