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Unformatted text preview: Lesson 07 Lesson 7 Challenge 6 Lesson 7 Aliasing What is it? How do you measure it? Challenge 7 Lesson 07 Challenge 6 T minutes = 0.5*10 9 Bytes * 1/4 sample/Byte * 1/44100 seconds/sample * 1/60 minutes/second ~ 47.25 minutes (average lecture time). In an average semester = ( 36) 47.5 minute lectures = 18GBy storage Need compression: For real world voice and image signals, Fourier or Fourier like methods are used (MP3 uses Direct Cosine Transform inspired by the Fourier Transform) 0.5GBy 44.1kSa/s 4 Bytes/word Lesson 07 Sampling Theorem Sampling Theorem Revisited If x(t) is baseband limited from above by some f max , If x(t) is periodically sampled at some rate f s , where f s > 2f max ; T s =1/ f s Then x(t) can be reconstructed (interpolated) from the sample values x[kT s ]. Lesson 07 Sampling Modalities f max /2 is called the Nyquist frequency. Sampling modalities over sampling f s >> 2f max (common case) critical sampling f s = 2f max undersampled f s < 2f max Lesson 07 Lets Give it a Test Oversampled Chirp Sweep :01,000Hz in 2 sec. Sample rate 8000 Lesson 07 Undersampled Sweep: 016,000Hz in 2 sec....
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 Spring '08
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 Aliasing

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