One of the purposes of CBI is to train students in the knowledge bases and in the problem solving strategies that characterize a discipline. As Section 1 suggested, a computer system may not always permit a student to express his or her knowledge of a subject area because the types of inputs that a system accepts may not express the structure of that knowledge. The keyboard and the mouse are standard input devices for most microcomputer systems. PowerPC computer systems now include speech recognition hardware that enables a student to give simple commands or responses to the computer in English.
Music CBI systems have their own special limitations in interacting with students. Although subjects such as sight singing and keyboard harmony are integral parts of university music curricula, a student cannot express his or her knowledge of these subjects with a computer keyboard or with a mouse. The CBI system must be able to hear a student singing or observe the student playing a piano keyboard. The ready availability of MIDI keyboards has given music CBI a tool for addressing one of these subjects. This section discusses the design of a pitch detector that enables a microcomputer system to listen to a student singing and to respond in real time.
This section addresses the many problems inherent in designing a pitch detector for a music CBI system. Not only should such a peripheral be affordable, but it also must accurately recognize the pitches that a student performs and it must do so with little or no perceptible delay. If such systems were easy to design, they already would be widely available. One reason that they are not is that psychologists and acousticians do not completely understand how humans perceive pitch. This section briefly discusses strategies for pitch extraction that other researchers have used. It then discusses a design that serves the needs of music CBI and meets most of the constraints of this discipline. This pitch detection system is also discussed in Clendinning (1983), Clendinning and Dworak (1982), and Dworak and Clendinning (1983).
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