ghettosynth wrote: fmr wrote:
aciddose wrote: In that sense ring mod is like FM; AM is like vibrato.
AM is NOT
like vibrato. AM is tremolo
Vibrato is modulation applied to frequency (by a low frequency oscillator). Tremolo is modulation applied to amplitude (by also a low frequency oscillator).
RM, when thought of as is it used in synthesizers, is a form of AM. While what results from any modulation process is some combination of the input frequencies, there is a subtle technical difference. In FM modulation, the frequency of the carrier is being modulated. In AM and RM, the amplitude of the carrier is being modulated.
I didn't deny that RM is "a form of AM". Actually, the mistake I pointed, and that caused my post, was calling vibrato to AM, a very common mistake. When using a low frequency oscillator, we can have vibrato if we modulate the frequency. But if we modulate the amplitude what we have is called tremolo, NOT vibrato. And the result is not the same, alhtough it may be close in certain circumstances. acidose post is basically correct, except when he says that thing about vibrato, and when he compares RM and FM. These two are quite different, even sonically.
About the difference between RM and AM in synthesis terms - Let's grab some help from Curtis Roads, and the book "The Computer Music Tutorial":
"Like RM, AM generates a pair of sidebands for every sinusoidal component in the carrier and the modulator. .../... The sonic difference between RM and AM is that the AM spectrum contains the carrier frequency as well. The amplitude of the sidebands increases in proportion to the amount of modulation, but never exceeds half the level of the carrier
This is the main difference. In RM, the carrier frequency disappears, according to Curtis Roads, when the frequency of the modulator is in the audible range (which is when we actually have "our" RM synthesis). Even if it doesn't disappears, as some here said, certainly its frequency will me much lower than the one of the sidebands, resulting in quite different spectra. AM will always be much "mellower", which is indeed what we can easily check in real life, and maybe the reason why it doesn't get so much interest as RM and FM.
Furthermore, if C and M are an integer ratio of one another, the sidebands generated are harmonic. Otherwise, they are inharmonic. That's why RM is often used to produce sounds that are difined as "clangorous" or "metallic".
Another curious effect mentioned is that, in analog implementations, depending on the type of diodes, the circuits introduce extraneous frequencies. One example quoted is that, in circuits based is silicon diodes, the diodes clip the carrier, truning it into a quasi-square wave, when it reaches the momentary level of the modulator, creating the effect of several sums and diferences on odd harmonics of the carrier (maybe this is where the "clangorous" effect comes from).
AFAIK, nothing of this happens in "pure" AM.
Last edited by fmr on Fri Aug 11, 2017 11:03 am, edited 1 time in total.