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How are the amplitudes of FM sidebands calculated?

E.g. when negative frequencies are reflected back and their amplitudes added to any existing positive frequencies at that band, how are the amplitudes of the sidebands (+ and |-|) calculated?

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some_id
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  • I don't think I understand your question. Could you make a drawing of the spectrum you're talking about, and add it, alongside with a few formulas referencing that drawing? – Marcus Müller May 25 '16 at 14:06
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    A sideband doesn't have an amplitude; a signal has, so we'll need to first "sync our vocabulary"; that's why I need that drawing. – Marcus Müller May 25 '16 at 14:06
  • What I mean is if a frequency is below zero, and reflected so its positive, how can the amplitude of the sideband be calculated for the positive and reflected parts? Yes the signal has an amplitude, but each frequency sideband also has an amplitude inside of the signal. The carrier's amplitude decreases as the modulator's amplitude increases. I guess that leads to my other question, how is the strength of the sidebands calculated for the signal? Its easy to calculate where the sidebands are, but I dont get how to know how powerful they are. – some_id May 25 '16 at 14:31
  • Why is a frequency below 0 reflected to the opposite side? make a drawing. – Marcus Müller May 25 '16 at 14:32
  • each frequency sideband also has an amplitude inside of the signal really, no, unless you define "amplitude" as some property of a group of Fourier coefficients or something. – Marcus Müller May 25 '16 at 14:32
  • Do you know FM synthesis? – some_id May 25 '16 at 14:34
  • yes. That's why really really recommend you clarify the system you're considering. Sideband, amplitude and "inside he signal" are not the same words for me that they seem to be for you. I really don't mean to offend you – it's just that your question remains unclear. And since you're the one asking, I can only tell you to make it clearer. This far, I'm your whole audience, and your audience doesn't understand you. – Marcus Müller May 25 '16 at 14:37
  • haha :) ok. So I have read this http://www.sfu.ca/~truax/fmtut.html which explains a lot of the calculations and ratios etc. Audio software uses the absolute value to avoid negative frequencies and destructive noise in the synthesised sound. Sidebands can be calculated from the ratio and the carrier frequency. If I think of sidebands as a bucket in the FFT, with higher values representing more frequency presence in that range, how is the amount or strength of a frequency range calculated for FM sidebands? How can the reflected/absolute sidebands strength be separated from the summed + sideband – some_id May 25 '16 at 14:44
  • Let us continue this discussion in chat. – some_id May 25 '16 at 14:46

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