of Microprocessors

DIGITAL FILTERING 507
lowest frequency "feature" significantly affects the duration of the impulse
response. This means that the other features essentially ride along free.
Figure 14-19 shows several response curves and their associated impulse
responses, which should aid in understanding these properties. Note in
particular that, while an ideal low-pass or bandpass filter characteristic can be
achieved with this technique, the extremely long, slowly decaying impulse
response makes its application impractical. Any attempt to shorten the response
by truncation or smoothing off destroys the ideal cutoff shape. Because
of the long impulse response, the FFT filtering method should be used
when such idealized filtering functions are needed.
o
;;;
~ -10
UJ
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~ -20
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Cl.
:i -30
-40'----'----------------------_
FREOUENCY (kHz)
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~ -10
UJ
o
~-20
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Cl.
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