Definition of Problem
	¡ For level 1~level 2, suppose a sequence of meaningful units can be perceived by  Human Beings from the raw audio data as:                       {                 }    The problem is how to detect the same  sequence from the raw data automatically. ¡ For level 2~level 3, suppose the sequence obtained from low level signal processing is:{                 }     The problem is how to use high level knowledge to correct the error introduced by low level signal processing and get the sequence of                          {                  }