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DSP A Khoa học máy tính quan điểm P7

In everyday parlance a ‘filter’ is a device that removes some component from whatever is passed through it. A drinking-water filter removes salts and bacteria; a coffee filter removes coffee grinds; an air filter removes pollutants and dust. In electronics the word ‘filter’ evokes thoughts of a system that removes components of the input signal based on frequency. A notch filter may be employed to remove a narrow-band tone from a received transmission; a noise filter may remove high-frequency hiss or low-frequency hum from recordings; antialiasing filters are needed to remove frequencies above Nyquist before A/D conversion | Digital Signal Processing A Computer Science Perspective Jonathan Y. Stein Copyright 2000 John Wiley Sons Inc. Print ISBN 0-471-29546-9 Online ISBN 0-471-20059-X Filters In everyday parlance a filter is a device that removes some component from whatever is passed through it. A drinking-water filter removes salts and bacteria a coffee filter removes coffee grinds an air filter removes pollutants and dust. In electronics the word filter evokes thoughts of a system that removes components of the input signal based on frequency. A notch filter may be employed to remove a narrow-band tone from a received transmission a noise filter may remove high-frequency hiss or low-frequency hum from recordings antialiasing filters are needed to remove frequencies above Nyquist before A D conversion. Less prevalent in everyday usage is the concept of a filter that emphasizes components rather than removing them. Colored light is created by placing a filter over a white light source one filters flour retaining the finely ground meal entrance exams filter to find the best applicants. The electronic equivalent is more common. Radar filters capture the desired echo signals deblurring filters are used to bring out unrecognizable details in images narrow-band audio filters lift Morse code signals above the interference. In signal processing usage a filter is any system whose output spectrum is derived from the input s spectrum via multiplication by a time-invariant weighting function. This function may be zero in some range of frequencies and as a result remove these frequencies or it may be large in certain spectral regions consequently emphasizing these components. Or it may half the energy of some components while doubling others or perform any other arbitrary characteristic. However just as a chemical filter cannot create gold from lead a signal processing filter cannot create frequency components that did not exist in the input signal. Although definitely a limitation this should not