How does the ear pick which note to hear when hearing guitar vibrato

Question

When adding vibrato to a fretted note on an electric guitar, if I do so by bending the note up a semitone, I perceive as the pitch of the original note being modulated. When applying vibrato to a bend however I sort of bend up to the note from the semitone below but this I hear it as the sound of the higher pitch being modulated, despite it technically being the same as the pitch I'm not hearing in the original case.

I thought it might be my brain latching onto the start point of the vibrato as you typically bend up to pitch then release but it seems to be the same if I just start from the semi tone down.

Is this just an ambiguous sound that forces my brain just pick the most likely interpretation? If so why does it always pick the same option?

Answer 1

I found an excerpt from a chapter written by Johan Sundberg in The Psychology of Music, a compilation of articles, presumably all related to psychoacoustics.

Here are some quotes and explanations:

Although F₀ [the fundamental frequency of the note] varies regularly in such tones, the pitch we perceive is perfectly constant as long as the rate and extent of vibrato are kept within certain limits.

This means if a vibrato is too wide or too slow or too fast, it will not be perceived as vibrato of one note, but instead a fast glissando or glide back and forth. I doubt that human-generated vibrato is likely to ever be too fast, but electronic vibrato can easily be sped up to the point that it is actually frequency modulation that causes a dramatic change in timbre, as used in synthesizers.

Later:

Our conclusions are that the pitch of a vibrato tone is practically identical to the pitch of a vibrato-free tone with an F₀ equal to the geometric mean of the F₀ of the tone with vibrato.

That suggests that upwards vibrato from a fretted note should sound a bit sharp, and downwards vibrato from a bent note should sound a bit flat.

In your particular situation, you can't entirely trust your perception of pitch, because you are overly informed about how you're creating the sounds and therefore are susceptible to confirmation bias. By that I mean, you expect to hear a certain pitch and that can create the auditory illusion of hearing exactly the pitch you expect to hear.

That said, unless you're playing in an ensemble with other instruments that are playing the same nominal pitches as you, naive listeners are unlikely to notice the difference.

Answer 2

Could be a few things. The note you hear is often the one you want to hear - in tune with the accompanying chord and relevant to the melody. If the vibrato stays a little longer on the higher/lower note, that's coming out as a more important pitch.

Somehow, we tend to hear a fluctuating note as the highest part. For that reason, we often play the note we want a fret lower than it should be, so that giving it a semitone vibrato, it gives us the right note to hear. We may even start that with the string bent to pitch - a cunning, but not easy move.

There's probably a limit to the amount a note can be stretched upwards before we become aware that something's out of tune, but I'm not party to it.