Tone.js/test/helper/compare/Spectrum.ts

import { TestAudioBuffer } from "./TestAudioBuffer.js";
import windowing from "fft-windowing";
import ft from "fourier-transform";

/**
 * Return a spectrogram of the buffer
 */
export function analyze(
	buffer: TestAudioBuffer,
	fftSize = 256,
	hopSize = 128
) {
	const spectrogram: number[][] = [];
	buffer
			.toMono()
			.toArray()
			.forEach((channel) => {
				for (
					let index = 0;
					index < channel.length - fftSize;
					index += hopSize
				) {
					const segment = windowing.blackman_harris(
						channel.slice(index, index + fftSize)
					);
					spectrogram.push(ft(segment));
				}
			});
	return spectrogram;
}