Fluency%20with%20IT

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JPEG images
Representing avg. pixel colour for large vs.
small blocks
Idea behind the Fourier transform Pixel values
2 3 3 4 8 7 3 2
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Fourier transform
Takes a function f(x)
Represents it as amplitude/frequency
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JPEG compression
Small bits for amplitude of high frequency
functions
Large bits for amplitude of low frequency
functions
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Digitizing Sound

• An object creates sound by vibrating in a medium
  such as air
• Vibrations push the air
• Pressure waves emanate from the object and
  vibrate our eardrums
• The force, or intensity of the push determines
  the volume
• The frequency (number of waves per second) is the
  pitch

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Sampling

• Take measurements at regular intervals
• Number of samples in a second is the sampling
  rate
• The faster the rate, the more accurate the
  recording

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MP3 compression
Use psychoacoustic model to eliminate sounds that
cannot be heard.
Experiment (T26) Pure tones that are close
together in pitch mask each other better than
those widely separated. To demonstrate this
fact, a single tone is played, followed by the
same tone and a higher frequency tone. The higher
frequency tone is reduced in intensity first by
12 dB, then by steps of 5 dB. The sequence above
is repeated twice. The second time the frequency
separation between the tones is increased
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MP3 compression
Use psychoacoustic model to eliminate sounds that
cannot be heard.
Experiment Pure tones also mask higher
frequencies better than lower frequencies. Track
27 and 28 attempt to mask high and low
frequencies respectively. The higher frequencies
will mask more easily than the lower frequencies.