651Appendix A
Audio Concepts, Terminology,
and Codecs
This appendix will help get you to get up to speed on the foundation of audio, as well as on digital
audio concepts, terminology, and codecs (file formats) supported in the Android OS.
I added this appendix to make sure that you have a deep understanding of the digital audio new
media assets that you will be creating, optimizing, and eventually “rendering” using Android’s digital
audio compatible classes such as SoundPool, MediaPlayer, Uri and MediaController.
Analog Audio and Digital Audio: History, Concepts,
and Theory
For developers to use digital audio assets wisely and optimally, they will need to know the basic
foundation of both analog audio and digital audio—where they came from, why they do what they
do, and how to harness them. I felt that this book would not be complete without an in-depth
discussion of analog and digital audio.
Foundation of Analog Audio: Sound Waves of Air
Those of you who are audiophiles already know that sound is created by sound waves pulsing
through the air. This is the reason you see sub-woofers with massive 18- to 30-inch cones rapidly
pushing out thunderous sound waves into audiences containing thousands of screaming fans at
rock concerts. Before the digital audio industry existed, the analog audio industry was a major
consumer electronics force. In fact, it still is today, with sound waves being controlled by complex
analog electronics products, featuring capacitors, resistors, oscillators, crystals, vacuum tubes, circuit
boards, mylar speaker cones, cardiod microphones, and similar analog audio creation technologies.