For most of a century, the telephone could not carry the pitch of your voice. The network passed roughly 300 to 3,400 hertz — bandwidth was expensive — and the fundamental frequency of nearly every human voice sits below that floor. A man speaking at 110 hertz was sending nothing at 110 hertz. Yet nobody's father ever arrived an octave up. You heard him low and whole. You heard a note that was never sent.
Psychoacousticians call it the missing fundamental. A tone's harmonics stack at multiples of its base — 220, 330, 440 — and your auditory system, handed only the upper floors, rebuilds the ground floor from their spacing. It isn't guessing politely, either. Mask the region where the fundamental would be and you hear it anyway. The pitch is not in the signal. The pitch is a conclusion.
Organ builders were exploiting this centuries before anyone could explain it. A true 32-foot pipe — the kind that makes a cathedral floor tremble at 16 hertz — costs a fortune and needs a tower to live in. So more modest churches bought a "resultant": a 16-foot pipe and its fifth, sounding together. No pipe in the building plays that bottom C. The congregation hears it anyway — almost feels it, that pressure under the hymn — a note assembled somewhere past the eardrum, from evidence.
I keep circling where that note is. Not in the pipes. Not in the wire. Not in the air, which carries only the hints. It plays in you, or it doesn't play anywhere.