function Melody(str, tempo) {
    this.tempo = tempo;
    this.notes = [];
    this.octave = 4;
    this.lastNote = null;

    // parse the melody string...
    var l = str.length;
    var cCode = 'C'
    str = str.toUpperCase();
    for (var i = 0; i < l; ++i) {
        var c = str.charAt(i);
        if (c >= 'A' && c <= 'G') {
            if (this.lastNote != null) {
                this.notes[this.notes.length] = this.octave * 12 + this.lastNote - 48;
            }
            var noteInOctave;
            switch (c) {
                case 'C': noteInOctave = 0; break; 
                case 'D': noteInOctave = 2; break; 
                case 'E': noteInOctave = 4; break; 
                case 'F': noteInOctave = 5; break; 
                case 'G': noteInOctave = 7; break; 
                case 'A': noteInOctave = 9; break; 
                case 'B': noteInOctave = 11; break; 
            }
            this.lastNote = noteInOctave; 
        } else if (c >= '0' && c <= '9') {
            this.octave = parseInt(c);
        } else if (c == '+' || c == '#') {
            this.lastNote++; 
        } else if (c == '-') {
            this.lastNote--; 
        } else { // any other char is counted as a rest
            this.lastNote == null;
        }     
    }
    this.notes[this.notes.length] = this.octave * 12 + this.lastNote - 48;
}
Melody.prototype.noteFrequency = function (noteNum) {
    return 440 * Math.pow(2, (noteNum-9)/12);
}
Melody.prototype.getCurrentFrequency = function (t) {
    var currentBeat = Math.floor(t * this.tempo / 60); 
    return this.noteFrequency(this.notes[currentBeat]); 
}
Melody.prototype.length = function () { // returns score length in seconds
    return this.notes.length * 60 / this.tempo;
}