Chapter 2 — The body before the ear

Pinna, canal, head, HRTF

A sound wave arrives at the side of your head as a pressure fluctuation in air. It does not arrive at the eardrum yet. It arrives at the outside of your body, where it is filtered, shaped, and split into two slightly different signals — one to each ear — before any neuron has any chance to do anything about it. The brain’s eventual sense of where the sound came from is built almost entirely from the differences between those two signals, plus the spectral fingerprint that the body’s outer geometry leaves on each.

This movement is about the acoustic transformations the body performs before the ear. They are subtle, ancient, and extraordinarily informative.

Anatomy of the human ear (preview)
Open 3D ear model in a new tab ↗ U.S. DoD Hearing Center of Excellence — fully interactive 3D model
Use the 3D viewer for anatomy reference whenever a written description leaves something fuzzy. The inline 2-D diagrams in this essay show only what we need for the current argument.