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 Nyquists Sampling Theorem Sampling Frequency is Very Important in order to accurately reproduce a digital version of an Analog Waveform Nyquists 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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03_CM0340_DataRep_Audio - 65 JJ II J I Back Close Digital...

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