Pitch Perception
Play the harmonics of a note and leave out the note itself, and you will hear the note anyway. Your brain reconstructs it from the pattern. One button settles what a page of theory cannot: pitch is something you build, not something you receive.
- the missing fundamental
- your brain fills it in
- one button proves it
Where you run into this
- Production
- Mixing
- Hearing science
- Instrument design
In short
Your auditory system recognises the spacing of a harmonic series and infers the fundamental that would produce it. If the spacing is there, the pitch is there, even when the frequency itself has been removed. This is not an illusion in the trick sense; it is how hearing normally works, and it is why a small phone speaker that cannot reproduce low notes still lets you hear a bass line.
The moment you add the fundamental back and the pitch does not change is the moment the subject lands. You expected it to appear, and instead something else got fuller.
How it works
Pitch perception explains several things that otherwise look like separate curiosities: octave equivalence, why we name notes in cycles of twelve, and why a note can be identified from a fraction of a second of sound.
Where you run into this
- A bass line that is audible on a laptop speaker that cannot produce those frequencies
- A telephone voice that still has the right pitch despite a narrow frequency range
- A church bell, whose named pitch is often not the loudest thing in the sound
Our own examples
Three demos: the harmonics above a missing fundamental, the fundamental added back so you can hear that the pitch was already there, and a single sine at that pitch for comparison.