meyda/dist/node/windowing.js

Real-time feature extraction for the web audio api

'use strict';

function blackman(size) {
    var blackmanBuffer = new Float32Array(size);
    var coeff1 = (2 * Math.PI) / (size - 1);
    var coeff2 = 2 * coeff1;
    //According to http://uk.mathworks.com/help/signal/ref/blackman.html
    //first half of the window
    for (var i = 0; i < size / 2; i++) {
        blackmanBuffer[i] =
            0.42 - 0.5 * Math.cos(i * coeff1) + 0.08 * Math.cos(i * coeff2);
    }
    //second half of the window
    for (var i = Math.ceil(size / 2); i > 0; i--) {
        blackmanBuffer[size - i] = blackmanBuffer[i - 1];
    }
    return blackmanBuffer;
}
function sine(size) {
    var coeff = Math.PI / (size - 1);
    var sineBuffer = new Float32Array(size);
    for (var i = 0; i < size; i++) {
        sineBuffer[i] = Math.sin(coeff * i);
    }
    return sineBuffer;
}
function hanning(size) {
    var hanningBuffer = new Float32Array(size);
    for (var i = 0; i < size; i++) {
        // According to the R documentation
        // http://ugrad.stat.ubc.ca/R/library/e1071/html/hanning.window.html
        hanningBuffer[i] = 0.5 - 0.5 * Math.cos((2 * Math.PI * i) / (size - 1));
    }
    return hanningBuffer;
}
function hamming(size) {
    var hammingBuffer = new Float32Array(size);
    for (var i = 0; i < size; i++) {
        //According to http://uk.mathworks.com/help/signal/ref/hamming.html
        hammingBuffer[i] = 0.54 - 0.46 * Math.cos(2 * Math.PI * (i / size - 1));
    }
    return hammingBuffer;
}

exports.blackman = blackman;
exports.hamming = hamming;
exports.hanning = hanning;
exports.sine = sine;