I solved it calling a method of the "userdata" object instead of emitting a signal so:

Qt Code: 
  1. //! Executed when a sound finish playing
  2. FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
  3. 								   unsigned int commanddata1, unsigned int commanddata2)
  4. {
  5. 	(void)commanddata1; // Unused (to avoid warnings)
  6. 	(void)commanddata2; // Unused (to avoid warnings)
  7.  
  8. 	WaveWidget* wave;
  9.  
  10. 	switch(type)
  11. 	{
  12. 	case FMOD_CHANNEL_CALLBACKTYPE_END:
  13. 		{
  14. 			FMOD_RESULT result;
  15. 			FMOD::Channel *currentChannel = (FMOD::Channel *)channel;
  16.  
  17. 			void *ud = NULL;
  18. 			result = currentChannel->getUserData( &ud ); // Here I get the userdata
  19.  
  20. 			wave = (WaveWidget*)ud; // I cast it
  21. 			wave->stopTimer(); // Call userdata method
  22.  
  23. 			//emit AudioDevice::getInstance()->soundStopped(); //inform that sound is stopped
  24. 			break;
  25. 		}
  26. 	default:
  27. 		break;
  28. 	}
  29.  
  30. 	return FMOD_OK;
  31. }
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Bye