Chapter1-1

Chapter1-1 - Spring 2009 ELEC001 Electronic Information Technology Chapter 01-Time and Frequency Domain Representation of Signals P.1 Signal is

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P.1 Chapter 01 -- Time and Frequency Domain Representation of Signals Spring 2009 ELEC001 Electronic & Information Technology
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Signal is everywhere Signal: A pattern or variation that contains information. It is what human can see, hear, touch, smell, taste, and visualized Example: Audio, image, and video signal
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P.3 Signal is everywhere Hang Seng Index Signal in Finance Radio, cellular phone, and wireless LAN signal Particle Physics Tracks in a hydrogen bubble chamber
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P.4 Signal Conveys Information Computer Tomography Electrocardiogram X-ray Information arouse our senses, guide our decisions and courses of actions, and help in our pursuit of understanding of nature http://hk.youtube.com/watch?v=P_0kBD_4T6o
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P.5 Representation of Signal Before we discuss how to process signals we need to discuss how we represent (describe) signals. Often, signal is the variation of some physical quantity over time Variation of the Hang Seng Index over one year Audio Signal – Variation of Acoustic Pressure over 1/20 of a second 50 msec
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P.6 Representation of Signal Signal can also be variations of some physical quantity over space Lena – The standard picture in image processing Color and brightness of pixels (picture elements) over 2-dimensional space Tracks in a hydrogen bubble chamber
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P.7 Representation of Signal Signal can also be variations over both space and time. Example: video
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P.8 Some engineering notations (Prefix) Prefix Symbol Value tera T 10 12 giga G 10 9 mega M 10 6 kilo k 10 3 (no prefix) 10 0 milli m 10 -3 micro μ 10 -6 nano n 10 -9 pico p 10 -12 Examples: “4 GB” USB flash memory, “5M Pixels Digital Camera”, “10 Mbps broadband service.” Also, you heard about “nanotechnology.” Nano, in fact, is an engineering notation for 10 -9 . In engineering and science we may encounter dimensions that can be very large or very small. So let us introduce the following notations before we begin our technical discussions
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P.9 Topics in this Chapter Example: Audio Signal and Frequency Frequency Domain Representation of Signal Processing of Signals - Filtering Electromagnetic wave – messenger given by Nature
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P.10 Audio signal (sound) Audio signal is a signal we can hear, through variation in the acoustic pressure that reaches our ears. In 1877, Alexander Graham invented the telephone, a device to convert audio signal from acoustic pressure into a varying electrical current that can be transmitted over wires. acoustic pressure moves a diaphragm that compresses the carbon granules and changes the amount of electricity that can pass through the circuit
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P.11 Audio Signal as Acoustic Pressure or Electrical Current Thus, audio signal can be viewed as a variation of acoustic pressure or electrical current as a function of time time Acoustic Pressure Electrical Current time 10 ms 20 ms 20 ms 10 ms The electrical signal is an almost exact replicate of the acoustic signal except for some distortion .
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P.12 Hearing and Plotting an Audio Signal Let’s hear an audio signal Plot of the audio signal as a function of time What are we actually hearing? What is “ sound ”?
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P.13
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This note was uploaded on 01/28/2011 for the course ELEC 001 taught by Professor Albertwong during the Spring '09 term at HKUST.

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Chapter1-1 - Spring 2009 ELEC001 Electronic Information Technology Chapter 01-Time and Frequency Domain Representation of Signals P.1 Signal is

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