     var lastKey: UIButton?
     var monoMode: Bool = false
     var holdMode: Bool = false
-    var keysHeld = [UIButton]()
     var midiNotesHeld = [Int]()
     let blackKeys = [49, 51, 54, 56, 58, 61, 63, 66, 68, 70]
     

        }
        
        if holdMode {
            if keysHeld.contains(key) {
                turnOffKey(key)
                return
            }

        }
    }
    
    // About App
    @IBAction func audioKitHomepage(sender: UIButton) {
        if let url = NSURL(string: "http://audiokit.io") {
