Phase modulation feedback averaging,yiehaa

gentleclockdivider

There has always been something that didn't quit sounded like the yamaha method of feedback phase modulation , when doing it in reaktor .
And thanks to the developer of Alpha modular ,I now finally know ..

It sounds so damn close to yamaha dx7 feedback
The feedback loop in all old skool yamaha fm synths are averaged , and can be considered as a verry simple fir filter in the feedback loop .

Also , the feedback coefficient on old dx synths have 8 possible values but that's another topic ( these are just feedback gain coefficients)

Now , feedback should ALWAYS be tapped after the operator has been scaled by it's envelope and it's gain coefficient ( some synths do this completely wrong , like oxe fm and even the reface dx ) because the envelope has a direct influence on the amount of gain that is fed back into the (feed ) loop but that's a different topic .

So here's the averaging in primary , take the current sample + previous sample and /2 .

Old method without averaging

With averaging

In core , I've used also used a sine function for the operator ( scale ramp by tau for a full sinewave cycle )
The averaging is done by using a write-read but the slave output of read obc should go in the master of write obc to get the previous sample , like this

Now , this is all nerdy stuff and I'm sure 99% won't notice the difference when it's not averaged ,but it's obvious on the scope ,when feed is averaged you can get a sharper saw wave before it starts breaking down into noise .

Just wanted to share my excitement , and big thanks to Alpha Forever Developer for pointing this out .

gentleclockdivider

Here's an old fm synth I made ( no snapshots possible thanks to N.I. for not fullfilling their promise when using on screen patch cables )
With the adjusted feedback scaling .

CablefmTX-feedaveraged.ens