Helpful bits for synthesizing/analyzing audio

synt_helper_functions.js

// The sample rate of your audio playback;
const RATE = 44100;

// Magic number!
var Hz = 2 * Math.PI / RATE;

// Frequencies of some notes
var freqTable = [16.35,17.32,18.35,19.45,20.6,21.83,23.12,24.5,25.96,
27.5,29.14,30.87,32.7,34.65,36.71,38.89,41.2,43.65,46.25,49,51.91,55,58.27,
61.74,65.41,69.3,73.42,77.78,82.41,87.31,92.5,98,103.83,110,116.54,123.47,
130.81,138.59,146.83,155.56,164.81,174.61,185,196,207.65,220,233.08,246.94,
261.63,277.18,293.66,311.13,329.63,349.23,369.99,392,415.3,440,466.16,493.88,
523.25,554.37,587.33,622.25,659.26,698.46,739.99,783.99,830.61,880,932.33,
987.77,1046.5,1108.73,1174.66,1244.51,1318.51,1396.91,1479.98,1567.98,1661.22,
1760,1864.66,1975.53,2093,2217.46,2349.32,2489.02,2637.02,2793.83,2959.96,
3135.96,3322.44,3520,3729.31,3951.07,4186.01,4434.92,4698.64,4978.03];

var notes = 'cCdDefFgGaAb';

// example usage:
// decodeNote('a4');
// > 57
// freqTable[57];
// > 440
function decodeNote(n) {
    var match = n.match(/(\w)(\d+)/);
    return notes.indexOf(match[1]) + match[2] * 12;
}

//example function
function generateSine(freq, duration) {
    var samples = new Float32Array(~~(duration * RATE));
    for (var i = 0; i < samples.length; i++) {
        samples[i] = Math.sin(i * freq * Hz);
    }
    return samples;
}