Figure 13'6'

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13.4 Transducing and Recording Sound

• Figure 13.6.
• Clipping of a signal (right) when the
  preamplifier has been set too high, so that the
  signal is outside of the -5 to 5 V range of the
  A/D converter.

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13.5 Aliasing and the Sampling Frequency

• Someone has an alias when they use more than one
  name (representation)
• In the world of signals, this means having more
  than one representation of an analog signal,
  because of inadequate sampling frequency
• Familiar visual aliasing from the movies (when 32
  frames per second is too slow)
• Wagon wheel / propeller going backwards
• Scan lines appearing on computer screen

• Inadequate Fs can result in aliasing for sounds
  too....

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13.5 Aliasing and the Sampling Frequency Visual
Signals
The Wagon-Wheel Effect film a fast
clockwise-rotating wheel/propeller at 24 frames
per second
0 sec
1/24 sec
2/24 sec
30.75 rotations
30.75 rotations
Perceive slow counter-clockwise rotation
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13.5 Aliasing and the Sampling Frequency Audio
Signals
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13.5 Aliasing and the Sampling Frequency

• Figure 13.8.
• Aliasing. A set of samples marked as circles.
  The three sine waves plotted are of different
  frequencies, but all pass through the same
  samples. The aliased frequencies are F m/?T,
  where m is any integer and ?T is the sampling
  interval. The sine waves shown are m 0, m 1,
  and m 2.