Digital Signal Processing Reference
In-Depth Information
to pass through.
Notch filter with cutoff freq 40%
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Figure 3.22: A notch lter.
Bandpass filter with cutoff freqs 20%, 40%, 60% and 80%
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Figure 3.23: Frequency magnitude response for a bandpass lter with two pass-
bands.
To see how a lter behaves, we can view a plot of its frequency magnitude
response, as we did above. To get the frequency magnitude response, rst perform
the Discrete Fourier Transform (DFT, Chapter 6, \The Fourier Transform") on the
lter coecients. These coecients may be zero padded to make the curves smooth.
An assumption is that the number of coecients passed to this function is less than
128, a convenient power of 2. The example below looks at two lters, a lowpass
lter and a highpass lter. We show only the rst half of the spectrum. The second
half will be only a mirror image, since the input signal is real.
