Increase polyphony to 24 voices

include/voicemanager.h

@@ -2,10 +2,11 @@
 #define __VOICEMANAGER_H__
 
 #include <unordered_set>
+#include <thread>
 
 #include "voice.h"
 
-#define NUM_VOICES 16
+#define NUM_VOICES 24
 
 class VoiceManager {
 public:
@@ -31,4 +32,4 @@ private:
     unsigned int scoreVoice(VoiceData& voiceData);
 };
 
-#endif
+#endif