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Green Xenon

Why is it called FM synthesis?

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Hi:

Most so-called "FM synths" actually use Phase Modulation Synthesis. So why are they still referred to as FM? Wouldn't it be more appropriate to call them "PM synths"?

Also, isn't the math involved in PM Synthesis significantly different from that in FM Synthesis?

Does studying the math of FM synthesis do much good when it is actually a PM synth you're trying to design/build?

Thanks,

Green Xenon

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Phase Modulation and Frequency Modulation are essentially two names for the same thing.

Phase Modulation modulates the frequency indirectly, while FM directly does the same.

If you look at it from the math side, it is in it's essence the same operation.

Plus, you cannot tell any difference from the spectrum analysis.

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I wouldn't hesitate to imagine that it is called FM because yamaha said so hehehehe

If they had called the DX range PM it would be known as PM simple as that ;)

Flexi

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I think some companies called it Phase Modulation (instead of FM) to avoid law suits from Yamaha, who protected FM quite vigorously.

But the Casio CZ synths which use Phase modulation of a Sine wave to achieve other wave forms is quite a bit different to say, the DX-7's FM architecture with it's many operators.

To me, the CZ's sound heaps more like an analogue than a digital synth. (A little off topic tho)

Regards

Mike

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The Casio CZ series use Phase distortion synthesis which is a different concept to Frequency or Phase Modulation, though it did produce similar results.

The main difference between FM and PM is that a DC offset in the modulator produces a pitch shift in the carrier with FM and only a phase shift with PM.  This makes a PM synth more stable.

See http://archive.cs.uu.nl/pub/MIDI/DOC/phase-mod for more information and some C source code.

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The main difference between FM and PM is that a DC offset in the modulator produces a pitch shift in the carrier with FM and only a phase shift with PM.  This makes a PM synth more stable.

I think another point is that with direct FM, operator feedback (to let an operator modulate its own frequency) would not be possible cause it would just cancel itself out or so. With PM this is possible. I read this somewhere in a Csound documentation I think, or the Csound Book.

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Does studying the math of FM synthesis do much good anyway?

Listen to the vibes man....the vibes....

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Does studying the math of FM synthesis do much good anyway?

Listen to the vibes man....the vibes....

I agree with you to a point.  If you don't know anything about the math of Yamaha DX-style FM synthesis you may get used to the character of certain operator frequency relationships and intuitively build nice sounds, but using algorithms with operators stacked more than 2 high becomes pure trial and error.

Yeah, the vibes must prevail, but it's the difference between spending 10 minutes and 10 hours to achieve the sound you're looking for.

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Does studying the math of FM synthesis do much good anyway?

Listen to the vibes man....the vibes....

synths.jpg

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nebula you are bang on there mate.

Of course itys trial and error when the operators get too many, but i doubt that any math will predict the sound you have in your head.

As an example, I want to make the sound of two sines (500 Hz mod, 800 Hz carrier) which, when FM'd, drive one side of a ring mod, the other side being driven by two sines (50 Hz mod, 300 Hz carrier), the resultant waveform then being used as a mod input to another FM, the carrier being a further sine (1kH).

Play around with the math all you like, I still prefer to twiddle da nobs.

cheers

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Yeah, the vibes must prevail, but it's the difference between spending 10 minutes and 10 hours to achieve the sound you're looking for.

Are you talking about PM vs. FM?

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Are you talking about PM vs. FM?

I'm talking about whatever it is that Yamaha called FM or AFM synthesis.

The sonic possibilities are vast.  You have so much control over so many subtleties of the sound that it is easy to get lost.

I have a Yamaha DX11, TX81Z, DX7 and a TG77.  Most of the presets I have created for these instruments were made when I was trying to achieve something else.  For example while trying to create a hand drum sound and you end up with a great mallet sound.  Or while you're on your way to building a certain bass sound, you end up with a great clav sound, so you save it as such and then keep working.

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just enjoy neb.

By the way, I thought you said it only took 10 mins to get the sound you want? It seems to me that you start with a mental sound but end with something entirely different.

Twiddle and learn.... the maths are far too complex and restrict the music juices.

regards

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Ah, ah... Whats wrong about this is that an average guitarist knows more about harmonics than your average techno dj, hence, the FM synth is in better hands  :P

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