old_contents: var WO = WO || {};
  WO.Song = Backbone.Collection.extend({
    model: WO.Track,
    
    settings : {
      tempo: 120,
      title: "untitled song",
      timeSignature: 4,
      length: "16:0:0"
    }
  
  });
  
new_contents: var WO = WO || {};
  WO.Song = Backbone.Collection.extend({
    model: WO.Track,
    
    settings : {
      tempo: 130,
      title: "untitled song",
      timeSignature: 4,
      length: "16:0:0",
      activeInstrument: ""
    },
  
    initialize : function(){
  
      this.add( new WO.Track());
      this.settings['activeInstrument'] = this.at(0);
      // WO.setTempo(this.settings.tempo);
    }
  
  });
  
subject: add activeInstrument functionality