# lecture3 - CSE 471 Media Processing and Multimedia Sampling...

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1 CSE 471 Media Processing and Multimedia Sampling and Quantization Capturing sounds electronically Sampling sounds Aliasing Quantization

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2 CSE 471 Media Processing and Multimedia Electronic capture of sounds N S
3 CSE 471 Media Processing and Multimedia Sampling Sampling - simply taking voltage readings at fixed points in time Uniform sampling – sampling at regular intervals

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4 CSE 471 Media Processing and Multimedia Sampling Real values at fixed points in time Uses a “sample-and-hold” Values are called “samples” Analog signal Sample and Hold Sampled signal Sample
5 CSE 471 Media Processing and Multimedia How might you measure waves on a beach? Or, even, sample the wave height

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6 CSE 471 Media Processing and Multimedia Is sampling okay? Question: Is a sampled representation the same thing? Yes, provided…
7 CSE 471 Media Processing and Multimedia The Sampling Theorem Given a uniform sample rate of f s , the highest frequency that can be unambiguously represented is f s /2 f s /2 is the Nyquist Frequency CD Players use f s =44,100 samples/sec The Nyquist Frequency is 22,050 Hz Why don’t CD’s sample at 40KHz?

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8 CSE 471 Media Processing and Multimedia Sound in the Real World Recall: All sounds can be expressed as a combination of sinusoids String instruments generate harmonics C8 on piano = 4186 Hz 6 th Harmonic is 25,116 Hz Above the Nyquist Frequency!! Many instruments generate content above 20 KHz ( 29 = + = 1 sin ) ( h h h t h c t f φ ϖ
9 CSE 471 Media Processing and Multimedia What happens above Nyquist Frequency? For now, we’ll use the term Aliasing

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## This note was uploaded on 07/25/2008 for the course CSE 471 taught by Professor Owen during the Fall '07 term at Michigan State University.

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lecture3 - CSE 471 Media Processing and Multimedia Sampling...

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