PreenFM > preenfm2 and preenfm3

Basic waveforms with FM

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Xavier:

--- Quote from: SMF on August 12, 2019, 05:34:39 PM ---Hi Xavier,
when I read this for the first time (in an older thread), I assumed it was a typo, but as you repeatedly say it's a low-pass filter, I am curious now... because for all what I recall, it is a high-pass filter which is required to get rid of the DC-component of the resulting spectrum in case of FM (PM does get rid of the DC-component inherently)...

--- End quote ---

Yes, sorry. It was a typo, it's a high pass filter, as you said to get rid of the DC-component.

TanaBarbier:
Hi everybody

I am really interested in this topic. I know I am digging an old thread but if someone has any info, or just want to geek out a little bit on FM vs PM...
How are those two technics so different ?

PM is something like : Pm(t)=a*sin(f*t+b*sin(f’*t))
Is FM like this : Fm(t)=a*sin(f*t*b*sin(f’*t))
Or like this : Fm(t)=a*sin(f*t*(1+b*sin(f’*t))    (So that you still get a sine wave when there is no modulation)
Or something else ?

I get that frequency modulation will introduce a change in pitch because of DC offset (or even a small difference between positive and negative part of the cycle), so high passing it gets rid of that. But what about spectrum, how is it different? I mean sidebands still appear at the same frequencies, don’t they? Are their amplitudes different? Don’t they follow the same Bessel functions ?
I have to say that I don’t think I hear the difference, (the frequency drift being taken care of by the HP), but what is actually different? (Signal looks like phases have been messed with, no feedback etc, what else?)

Any idea, place to look for those kind of stuff?

 A good day to everybody.

Xavier:
How i see the forumas is
  Pm(t) = a*sin( f  * t + b * sin(f' * t))
  Fm(t) = a*sin( (f + b * sin(f' * t)) * t)

In FM the above operator(s) modulate the frequency, in PM they modulate the phase (as expected ;) )

The DC Offset only occures if you have 3 operators in a row.
A High Pass filter is required on the middle operator.

To hear a difference between PM and FM, you also have to use 3 operators. Each OP modulates the one bellow.
Then the resulting sound will be  different.
I made the maths a long time ago, but i don't remember at all  ::)

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