Does FM scale or add to frequency

[avasopht]

Which of the two lines best describes FM?

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modulated= freq * (abs(fm) * sign(fm))
modulated= freq + fm

[camsr]

Isn't their two types? They are both correct but different. One of them is called Chowning FM.

[helium]

abs(fm) * sign(fm) = fm

So it's between "freq * fm" and "freq + fm". In that case "freq + fm" describes it better.

[antto]

i'm aware of 3 kinds of "FM"

freq += fm*depth
pitch += fm*depth
phase += fm*depth; // yamaha ;P~

[helium]

freq += fm*depth AKA Linear FM
pitch += fm*depth AKA Exponential FM
phase += fm*depth AKA Phase Modulation (used by most digital "FM" synths)

[MadBrain]

Use phase modulation.

Like, there's no contest, it's by far the most workable, useful type. Frequency modulation is basically phase modulation using the integral of the modulator (so for instance, frequency modulation by a square wave is just like phase modulation with a triangle wave) and it has the added defect that it easily goes out of tune (you cannot use 3 modulator stacks or feedback because it goes out of tune). Exponential frequency modulation compounds this problem by putting modulation on an exponential scale, so it's essentially always out of tune.

So the ACTUAL algorithm to "fm" (phase modulation) is:

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output = volume * carrier_wave[carrier_freq * t + modulation * modulator_wave[modulator_freq * t] ]