meyda/dist/node/extractors/spectralRolloff.js

Real-time feature extraction for the web audio api

'use strict';

function spectralRolloff (_a) {
    var ampSpectrum = _a.ampSpectrum, sampleRate = _a.sampleRate;
    if (typeof ampSpectrum !== "object") {
        throw new TypeError();
    }
    var ampspec = ampSpectrum;
    //calculate nyquist bin
    var nyqBin = sampleRate / (2 * (ampspec.length - 1));
    var ec = 0;
    for (var i = 0; i < ampspec.length; i++) {
        ec += ampspec[i];
    }
    var threshold = 0.99 * ec;
    var n = ampspec.length - 1;
    while (ec > threshold && n >= 0) {
        ec -= ampspec[n];
        --n;
    }
    return (n + 1) * nyqBin;
}

module.exports = spectralRolloff;