[sdiy] PM vs FM was: Re: Buchla 295 10-band comb filter topology

Ingo Debus igg.debus at gmail.com
Thu Dec 1 21:48:53 CET 2022

> Am 01.12.2022 um 20:37 schrieb Donald Tillman <don at till.com>:
> So let's try an experiment.  I've got a DX7II-FD here.  It's been a long time; dusty, presets rotted away, 'forgot how to use the thing...
> Okay, Alg 3.
> Op2, 2x frequency, level 70
> Op1, 1x frequency.

:-) Dug that book out and did the same thing yesterday on my DX7 (anyone else?).
Boy, that thing is almost 40 years old. The second battery is probably dead, the volume pot is a bit scratchy, but the rest works just fine. Built like a tank.

> One of the cool things you can do with PM is to use an audio signal to modulate a low frequency oscillator.  (Huh?  That sounds so backwards.)  This creates a phase shifty chorus sound, so it's a sweet trick for Hammond patches.

Yes, and that is *the* real shortcoming of Yamaha’s four-operator FM synths. On the early ones the operators could not be set to „Fixed Frequency“ at all. I had a TX81-z, which did have „Fixed Frequency“ mode, but the lower limit was at 8 Hz! What were they thinking??
On the later models, SY77 etc., Fixed Frequency could even be tuned down to 0.

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