Silicon, Circuits, and the Digital Revolution
Sound and Its Digitization
- Storage of text information
- ASCII: American Standard Code for Information Interchange
- Demonstration of sample text (sample.txt)
- Demonstration of sound waves
- Oscilloscope output of electrical signal driving speaker>
- Variation of frequency of audio generator
- Effects of enclosing speaker
- Effects of resolution (number of bits of digitization)
- Effects of sampling rate (number of digitizations per second)
- Slide Show of sampling issues
- Another Slide Show showing aliasing
- Nyquist Sampling Criterion:
- a waveform must be sampled at a rate at least twice its highest frequency to avoid aliasing
- Playing time of an audio compact disc
- Recall that storage capacity is 650 Mb (megabytes)
- 2 bytes per sample of sound (16 bits)
- 2 channels for stereo sound => 4 bytes per sample
- Thus a CD can store 160 million audio samples.
- Since the human hear only hears up to 22 kHz (22,000 cycles/sec),
a sampling rate of 44 kHz is used for sampling audio (Nyquist sampling criterion!).
- The time elapsed in making 160,000,000 samples at a rate of 44,000 samples per second is 3600 sec.
- This is 1 hour, the nominal playing time for an audio CD (actually 74 minutes).
Comments, suggestions, or requests to firstname.lastname@example.org.
Last updated November 29, 2004.
© George Watson, Univ. of Delaware, 2000.