See what sound looks like
Every sound is a stack of pure tones. Play one of the samples, or whistle into your microphone, and watch this page pull the tones apart and paint them as they arrive.
Your microphone never leaves this page
How to read the picture
Left to right is time
The picture is drawn one thin column at a time, the way a seismograph draws. The right-hand edge is the newest sound.
Bottom to top is pitch
Low rumbles sit at the bottom, hiss and cymbals at the top. A note that slides upwards draws a line that climbs.
Bright means loud
A bright band is a strong tone; dark is silence at that pitch. One plucked guitar string draws a whole stack of stripes — the note itself, plus the overtones above it that make it sound like a guitar and not a flute.
Three things to try
See sound
Play a guitar note, a chord, a drum hit, or your own voice, and watch the picture build as it happens.
02Build a sound
Stack pure tones with sliders, hear the result, and check that the picture finds exactly the tones you put in.
03Check the maths
Run our transform beside the browser’s own on the same sound, and see for yourself how far apart the two answers are.
The one idea worth taking away
You cannot know exactly when a sound happened and exactly what pitch it was, both at once. Measuring a low note takes time — you have to watch several of its cycles go by — so the sharper the pitch, the blurrier the timing. Drag the detail control and you can watch the picture trade one for the other. It is the same mathematics as Heisenberg’s uncertainty principle, not a limitation of this page.
Start listeningYour microphone never leaves this page
Once loaded, this page makes no network requests at all — no analytics, no error reporting, nothing. Sound is analysed inside this tab and thrown away. The sample sounds are generated by code rather than downloaded, and a test in the repository fails the build if a single network call is ever added.
Written by hand, on purpose
Browsers already ship a Fourier transform, and a spectrogram built on top of it takes ten lines and teaches nobody anything. The transform here is written from scratch — the same Cooley-Tukey algorithm from 1965 — and checked four independent ways: against the textbook definition, against a conservation law, by running it backwards, and against signals whose answers are known in advance.