     @IBAction func keyPressed(sender: UIButton) {
         let key = sender
         
+        // Turn off last key press in Mono
         if monoMode {
-            if let lastKey = lastKey where lastKey != key {
+            if let lastKey = lastKey {
                 turnOffKey(lastKey)
             }
         }
         
+        // Toggle key if in Hold mode
         if holdMode {
             if midiNotesHeld.contains(midiNoteFromTag(key.tag)) {
                 turnOffKey(key)

    func toggleMonoKeyHeld(key: UIButton) {
        if midiNotesHeld.contains(midiNoteFromTag(key.tag)) {
            midiNotesHeld.removeAll()
            midiNotesHeld.append(midiNoteFromTag(key.tag))
        } else {
            midiNotesHeld.removeAll()
        }
    }
    

    func turnOffHeldKeys() {
        updateAllKeysToUpPosition()
        
        for note in 21...108 {
            conductor.core.stopNote(note)
        }
    
