In synthesising a musical note consisting of multiple pure tones combined, what is the perceptual effect of giving all tones in the note the same vibrato and/or tremolo?
Definition of vibrato I'm using is a periodic change in the pitch of a note. What happens when a musical note consisting of a multiple of pure tones is subject to vibrato? I'm answering this way because the perceptual effect of what happens may vary between different listeners.
Listener 'A' may hear something gliding back and forth whereas Listener 'B' may notice volume changes as the note is periodically altered. The volume change is usually called tremelo and all the notes in the "sound" will rise and fall in amplitude by the same amount if the sound is synthesized in a simple way BUT, synthesis of a tremelo effect may be subtler and vary some of the multiple pure tones in amplitude more or less than others - this of course raises or lowers the overall volume but, will also lead to timbral variations in the sound and this may produce effects that are more like a real instrument.
Vibrato changes pitch and my take on it is this; if you have a set of synthesized pure tones that make up the sound, the ratio of each tone relative to the lowest note creates a certain timbre (ignoring their relative amplitudes) - natural instruments like violins, guitars (all of them I suppose) owe their distinctive sound to the harmonics superimposed upon the lowest note. These harmonics are exact multiples of the frequency of the base note and so vibrato should affect all the individual tones equally. By equal I mean if the base note shifts up and down 1% in frequency then the harmonics should also OR, you'll end up with different musical intervals and a clashing harmonically.
I'm not saying you shouldn't do this - I'm saying that, in the main, a natural instrument when subject to vibrato wouldn't do this.
You may, of course be synthesizing fifths or thirds and in this instant you definitely won't want to be drifting the individual tones at different percentages to the base note.