1. Dr. Jie ZouPHY 10711 Chapter 21 Musical Sound Noise corresponds to an irregular vibration of the eardrum produced by some irregular vibration. The sound of music has a different character, having periodic tones-or musical “tones”. Musicians usually speak of musical tones in terms of three principal characteristics: pitch, loudness, and quality.

2. Dr. Jie ZouPHY 10712 Pitch The pitch of a sound relates to its frequency. Rapid vibrations of the sound source (high frequency) produce a high note, whereas slow vibrations (low frequency) produce a low note. Different musical notes are obtained by changing the frequency of the vibrating sound source.

3. Dr. Jie ZouPHY 10713 Sound intensity and loudness The intensity of sound depends on the amplitude of pressure variations within the sound wave. –Sound intensity is a purely objective and physical attribute of a sound wave and can be measured by various acoustic instrument. Loudness is a physiological sensation. The ear senses some frequencies much better than others. –For example, a 3500-Hz sound and a 125- Hz sound with the same intensity, the 3500-Hz sound sounds about twice as loud to most people as the 125-Hz sound- humans are more sensitive to the 3500-Hz range of frequencies.

4. Dr. Jie ZouPHY 10714 Musical instrument Conventional musical instruments can be grouped into one of three classes: –Those in which the sound is produced by vibrating strings –Those in which the sound is produced by vibrating air columns –Those in which the sound is produced by percussion-the vibrating of a two-dimensional surface.

5. Dr. Jie ZouPHY 10715 In a stringed instrument such as a violin, the vibration of the strings is transferred to a sounding board and then to the air.

6. Dr. Jie ZouPHY 10716 In a wind instrument, like a flute, the sound is produced by a vibrating air column in the instrument. The musician blows air against the edge of a hole to produce a fluttering stream that sets the air column into vibration.

7. Dr. Jie ZouPHY 10717 In percussion instruments, such as a drum, a two- dimensional membrane or elastic surface is struck to produce sound.

8. Dr. Jie ZouPHY 10718 Homework Chapter 21, P. 406-408, Exercises: 8, 26, 27, 30. The above problems are assigned from the 10 th edition of the textbook by Hewitt.