The Microphone Sound Analyzer JavaScript Model records the sound from a computer or mobile device microphone and displays its amplitude and frequency spectrum.  Users can vary the recording length by selecting the number of data points. The number of points must, however, be a power of 2 in order to utilize the audio processor's Fast Fourier Transform (FFT) to compute the sound's frequency spectrum.  Because the domain of the computed frequency spectrum is usually too large for audio signals between 20 Hz to 20 kHz, users can set the minimum and maximum values on the graph to display only the range of interest.

The Microphone Sound Analyzer is designed for classroom demonstration and student experimentation. It was developed using the Easy JavaScript Simulations (EjS) version 5.3 and is distributed as a ready-to-run html page and requires only a browser with JavaScript support. This model runs on all platforms, including mobile devices, that support the W3C Media Devices API.

https://developer.mozilla.org/en-US/docs/Web/API/MediaDevices