03_CM0340_DataRep_Audio

03_CM0340_DataRep_Audio - 65 JJ II J I Back Close Digital...

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Unformatted text preview: 65 JJ II J I Back Close Digital Audio What is Sound? Source — Generates Sound • Air Pressure changes • Electrical — Loud Speaker • Acoustic — Direct Pressure Variations Destination — Receives Sound • Electrical — Microphone produces electric signal • Ears — Responds to pressure hear sound ( more later (MPEG Audio) ) 66 JJ II J I Back Close Digitising Sound (Recap from CM0268) • Microphone produces analog signal • Computer like discrete entities Need to convert Analog-to-Digital — Speed Hardware Also known as Sampling 67 JJ II J I Back Close Digital Sampling Sampling basically involves: • Measuring the analog signal at regular discrete intervals • Recording the value at these points 68 JJ II J I Back Close Sample Rates and Bit Size How do we store each sample value ( Quantisation )? 8 Bit Value (0-255) 16 Bit Value (Integer) (0-65535) How many Samples to take? 11.025 KHz — Speech (Telephone 8 KHz) 22.05 KHz — Low Grade Audio (WWW Audio, AM Radio) 44.1 KHz — CD Quality 69 JJ II J I Back Close Nyquist’s Sampling Theorem Sampling Frequency is Very Important in order to accurately reproduce a digital version of an Analog Waveform Nyquist’s Theorem: The Sampling frequency for a signal must be at least twice the highest frequency component in the signal. 70 JJ II J I Back Close Figure 1: Sampling at Signal Frequency 71 JJ II J I Back Close Figure 2: Sampling at Nyquist Frequency (Twice Signal Frequency 72 JJ II J I Back Close Figure 3: Sampling at above Nyquist Frequency 73...
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This note was uploaded on 01/26/2012 for the course CM 0340 taught by Professor Davidmarshall during the Fall '09 term at Cardiff University.

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03_CM0340_DataRep_Audio - 65 JJ II J I Back Close Digital...

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