0.4 Jbs2000-what is sound?

Table of contents

• Preface
• General background information
• Discussion
  • What is sound?
    • Vibration
    • Sensing vibration
  • Creating sound with a hammer
  • Creating sound with a computer
    • An object of a class
    • Alternating positive and negative values
  • Sine and cosine functions
    • Populating the array
    • The shape of a sinusoid
    • An audio graph of a sinusoid
    • Points on graph
    • A dual purpose
• Miscellaneous

Preface

This module is part of a collection titled Accessible Objected-Oriented Programming Concepts for Blind Students using Java . It explains some of the physical aspects of sound ina format that is accessible to blind students. It also explains a little about the trigonometric sine and cosine functions and suggests that they canbe used to create sound with a computer. An audio file is provided where audio pulses of different frequencies are used to represent points on agraph of a sinusoid.

General background information

By this point in the course, you should have learned enough that you can put Java OOP to work in a substantive way. Normally at this point, mysighted students would begin using OOP to manipulate the pixels and colors in digital images. That is not well suited to teaching OOP to blind students.In this course, which is designed specifically for blind students, you will begin writing substantive programs that deal with something that you areprobably very good at -- sound.

For example, you will soon learn how to write a Java OOP program to produce simple sounds such as TonesStereo .

(Note that if you are viewing the HTML version of this module on the Legacy site, you should be able to download this file and the other audio files in thismodule and play them using any standard media player that supports audio files of type AU. However, if you are on the OpenStax site, or ifyou are viewing the PDF version of this module on either site, you may not be able to download the file.)

As you study future modules in this collection, you will learn to write OOP programs to produce more complex sounds such as StereoPingpong .

Ultimately you will learn to write OOP programs that can be used to compose and play various melodies such as the following:

• FourScales
• MaryHadALittleLamb
• Greensleeves

Discussion

What is sound ?

An old physics question goes something like this. If the earth were populatedsolely by humans and a tree fell in the forest with no humans present, would it make a sound?

The answer is "No, it would not make a sound." The explanation follows.

Vibration

Assume that someone strikes the top of a car with their hand. This would cause the metal roof of the car to startvibrating. That vibration would cause the adjacent air molecules to also vibrate causing them to collide with their neighbors. Those molecules would collide withtheir neighbors, and on and on. We can think of this as a wave of vibrating molecules propagating outward from the car.

This wave of vibrating molecules propagates outward at a speed of approximately one mile every five seconds and decreases in intensity as itpropagates out from the source. At some distance from the source, the intensity of the vibrations has decreased to an insignificant level.