Convert note to frequency

Note to Frequency

// Takes string of Note + Octave
// Example:
// var frequency = getFrequency('C3');

var getFrequency = function (note) {
    var notes = ['A', 'A#', 'B', 'C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#'],
        octave,
        keyNumber;

    if (note.length === 3) {
        octave = note.charAt(2);
    } else {
        octave = note.charAt(1);
    }

    keyNumber = notes.indexOf(note.slice(0, -1));

    if (keyNumber < 3) {
        keyNumber = keyNumber + 12 + ((octave - 1) * 12) + 1; 
    } else {
        keyNumber = keyNumber + ((octave - 1) * 12) + 1; 
    }

    // Return frequency of note
    return 440 * Math.pow(2, (keyNumber- 49) / 12);
};