Stereo Math

What a stereo image is doing, as pure numbers: correlation at lag zero on the meter convention (no mean removal), mid/side energies and the width ratio they imply, an L-R energy balance, the constant-power pan law Web Audio specifies for a mono input, framerate-independent meter ballistics, and the field geometry a pan cursor and a width spread are drawn with. Every function has a defined answer for silence, empty buffers, mismatched lengths and non-finite samples, and returns a finite number for all of them. No React, no DOM — testable in Node and safe to draw with on the server.