Description:
Computes a frequency modulation spectrum, returning a chord object. The carrier frequency C <carrier> is modulated by the modulating frequency M <modul> with modulation index I <index>.
<carrier> and <modul> may be expressed in midics (the default) or in freqs. In that case the menu <unit> must be set to 'Freq'. <index>, the modulation index, is a positive integer between 1 and 25.
The inputs <carrier>, <modul> and <index> may also be lists. In that case, the nth element in <carrier> is modulated by the nth element in <modul> using the nth element in <index>, and so on. The results are then merged into a chord object (by default) or a chord-seq object by selecting 'chordseq' in the menu <type>.
A short explanation of FM (Curtis Roads, the computer music tutorial, MIT press, Massachusetts, p. 227-230): In case the inputs are atoms, we have Simple FM or Chowning FM (Chowning 1973). FM between two sinusoids generates a series of sidebands around C. Each sideband is located at a distance equal to a multiple of M. When the ratio between C and M (the C:M ratio) is a simple integer ratio such as, for example, 3:2 or 4:1, FM generates harmonic spectra. This means that the sidebands are integer multiples of both M and C. When C:M is not a simple integer ratio, FM creates inharmonic spectra. The number of sidebands the bandwidth) of the FM spectrum is controlled by the modulation index I, etc.
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