PreenFM > preenfm2 and preenfm3

Newbie questions

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SirPrimalform:
Hi,

Not been using my PreenFM2 (or indeed FM/PM in general) for long and I'm still marvelling at the possibilities. There are a few things I'm wondering about though:

The LFO waveform 'saw' sounds a lot like a triangle and there's a noticeable absence of a triangle waveform in the list for the LFO. It seems like maybe it's just a triangle wave misnamed? It wouldn't make sense to have actual separate ramp and saw waveforms when we have positive or negative amounts in the matrix.

On the topic of operator feedback, I understand from other posts that feedback is very difficult to implement with genuine FM like the PreenFM2 uses as opposed to Yamaha's PM version. Assuming the sine waves use a phase accumulator and a look up table, would it not be possible to use PM to calculate the feedback even if the rest of the engine is FM? Forgive me if that's a very stupid question, I'm not a real programmer.

Also, is the S^2 waveform literally just an octave up sine wave? If so, I'm not sure what the point is (other than effectively increasing the range of the ratio to 32). Is there any other special use I'm missing? If not, I'm wondering if I might make a custom firmware build to replace it with a band limited triangle wave? The triangle with its quickly diminishing harmonics seems like an ideal compromise between the pure sine and the rich saw and square.

One last topic - how many harmonics are the saw and square waves bandlimited to? When played further down, the hard bandlimiting almost sounds like they're being tracked by a resonant filter. I assume it's because the ear finds the top harmonic conspicuous because there's nothing above it. I was experimenting with additively generating a saw with just the first 32 harmonics last night and found that it was more pleasing and less resonant sounding if the last few harmonics rolled off in volume so that the top one didn't stick out. If it's possible to change the S^2 wave to a triangle, I might change the saw and square in this way too.

kuzma_p:
Yeah, i can confirm that Saw isn't Saw but Triangle.

Xavier:
I confirm it too. Sorry for the confusion.
The Saw is a triangle.
And the "ramp" LFO is a saw  :)

s^2 is a sin*sin so it's one octave above sin and should have a different spectrum too.

Feedback is not that hard to implement. It requires a low pass filter to prevent pitch shifting. But preenfm2 already do that in algo with more than 2 Operator in cascade.
Problems is that it adds some CPU overhead that i cannot afford.
And where to add feedback in each algo ? Idealy on every operator... :)
Also feedback is less usefull when you can chose a waveform for each oscilator.

I made several tests with a mix of PM and FM but nothing was really worth it.
I decided to go without feedback.. I'll stick with that ;)

How many harmonics ?
The waveform are generated by this small java  program :
https://github.com/Ixox/preenFM2/blob/master/waveforms/waveforms.java
The answer is 20 harmonics for square and "triangle". The others are not bandwidth limited.
The problem is that i don't remember if i used the default value for the waveform currently in the firmware  ::)
Check with a spectrum analyser.
You can also use this code to rebuild you waveform with more or less harmonics and recompile your firmware ;)

Xavier

Xavier:
The answer is in the code, the order is written there :
https://github.com/Ixox/preenFM2/blob/master/waveforms/waves.c

So order : 20.
Reminder : square only uses every other harmonic so you'll find only 10 harmonics.

Xavier

SirPrimalform:
Well it's true we can select saw and noise for the operators, but feedback gives some nice intermediate states. The possibility of feedback on every oscillator would be amazing. Maybe for the PreenFM3 eh?

By sin*sin, do you mean they are effectively ring modulated? Either way, I'll have to experiment with it some more if it has some harmonics that I missed. I'd still like to try swapping in a triangle wave at some point if that's possible? What is the format the wave is required to be in?

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