Try the live page: load any number of audio tracks into the player, and click a track to play. Or see a quick YouTube walkthrough.
Back when I was a full-time broadcaster and spent my evenings in a windowless studio, one source of both fun and useful information was the "phase-o-scope," a single-purpose oscilloscope that worked only in "xy mode", showing the stereo spread of an audio signal by drawing Lissajous patterns.
The pattern for in-phase audio will group roughly around the line y=x (the diagonal line from top right to bottom left of the display), although tracks with a broader stereo signal will deviate more. A pattern oriented around y=-x (top left to bottom right) is a sign of phase cancellation.
| In-phase audio | Out-of-phase audio |
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The "extreme green" look is a tribute to the glowing green CRT display typical of an old oscilloscope.
Phase-o-scope is an ongoing project written in React.js. The oscilloscope portion is hand-coded using the html Canvas and Web Audio APIs, while the waveform and spectrogram at the bottom of the page use wavesurfer.js.