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Unformatted text preview: Physics 1240 Hall Chapter 3 Notes 1 Focus questions and learning goals Chapter 3 focus questions: 1. How can we make sound? 2. What are the physical differences between different ways of making sound? Chapter 3 learning goals. After studying this chapter, you should be able to: 1. Predict how the sound of various instrumentsparticularly string and wind instrumentswill change as you: (a) Make the instrument longer. (b) Tighten the instruments strings. (c) Strike, pluck or blow harder on the instrument. 2. Explain how you could change the pitch of an instrument by precisely an octave. 3. Explain whats so special to humans (and music) about an octave. 4. Explain why some percussion instruments tend not to have well defined pitch, but do have a sort of rough pitch. 5. Predict how that pitch depends on the size of the instrument. Explain what else might affect the pitch besides size. 6. Design a drum whose pitch you can change. 7. Explain why electric guitars are so quiet if theyre not plugged in. 2 Sound categories This chapter focuses on the production of sound (as opposed to propagation and perception). Its the first introduction in this course to broad categories of instruments. This chapter is fairly qualitative and descriptive. The discussion has some useful concepts and vocabulary, and sets us up for more detailed study of instruments in a few chapters. Note that were not looking to zoom in just yet! In the first section of the chapter, Hall tries to categorize sounds. This has some value, although frankly I think that for whatever categories you come up with, we can find interesting sounds that dont fit exactly in the categories. The first distinction is natural versus artificial . Were going to be mostly studying artificial sounds: this means sounds produced on purpose, by us, for some reason, generally musical. (Al- though artificial sounds could be produced for medical or other research reasons.) So, if Laurie Anderson records a buzzing bee and plays it in a concert, is that natural or artificial? What if she slows it down or distorts it to make sound cooler? 1 Physics 1240 Chapter 3 notes Then theres original versus reproduced . This has little to do with the sound itself, although well certainly be interested in the fidelity (honesty, faithfulness) of recorded sounds. This will come much later in the course! The author then introduces steady versus transient sounds. A steady sound is one that is close to periodic: it continues in the same way for many cycles. Unlike the sinusoidal waves shown in the book and in class, real waveforms are never perfectly periodic. Therefore all sounds are transient to some extent. Real waveforms start (attack) and end (decay). The amplitude may be fairly constant while the sound is playing, or it may vary, fade, rise and fall. Last chapter when we looked at waveforms, we started talking about issues of transience. If you look at figure 3.1 of the text, you see a note which is transient (it dies away after only about a dozen cycles), yet...
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This note was uploaded on 08/24/2010 for the course PHYS 1240 taught by Professor Holland,murray during the Spring '08 term at Colorado.
- Spring '08