Audio Visualizer

The browser runs the FFT — that is what AnalyserNode is for, and it costs nothing to download. Everything after it is C++ compiled to WebAssembly: 1024 linear frequency bins folded into logarithmically-spaced bands, smoothed by an envelope follower with a fast attack and a slow release, and watched by an onset detector that reports a kick once rather than once per frame it is loud.

Nothing is playing when the page opens, and the bars still move. That is a synthesized demo signal generated in C++, and the panel says so while it is running — a visualizer reacting to a sound nobody is playing is the genre's house style and it is a lie unless it tells you. Choose a file and the label changes with the source.

Your audio never leaves your browser. The file is decoded by the browser and analysed on this page; it is not uploaded, and there is no endpoint on this site that could receive it.