SCEN103 Class 22
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Sound and its Digitization
- Storage of text information
-- ASCII: American Standard Code for Information Interchange
-- Demonstration of sample text
(Using Xtree Gold and 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 disk
- 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.
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Last updated feb. 4, 1998.
Copyright George Watson, Univ. of Delaware, 1996.