cheb1ord(wp, ws, gpass, gstop, analog=False, fs=None)
Return the order of the lowest order digital or analog Chebyshev Type I filter that loses no more than gpass
dB in the passband and has at least gstop
dB attenuation in the stopband.
Passband and stopband edge frequencies.
For digital filters, these are in the same units as :None:None:`fs`. By default, :None:None:`fs` is 2 half-cycles/sample, so these are normalized from 0 to 1, where 1 is the Nyquist frequency. (:None:None:`wp` and :None:None:`ws` are thus in half-cycles / sample.) For example:
Lowpass: wp = 0.2, ws = 0.3
Highpass: wp = 0.3, ws = 0.2
Bandpass: wp = [0.2, 0.5], ws = [0.1, 0.6]
Bandstop: wp = [0.1, 0.6], ws = [0.2, 0.5]
For analog filters, :None:None:`wp` and :None:None:`ws` are angular frequencies (e.g., rad/s).
The maximum loss in the passband (dB).
The minimum attenuation in the stopband (dB).
When True, return an analog filter, otherwise a digital filter is returned.
The sampling frequency of the digital system.
The lowest order for a Chebyshev type I filter that meets specs.
The Chebyshev natural frequency (the "3dB frequency") for use with cheby1
to give filter results. If :None:None:`fs` is specified, this is in the same units, and :None:None:`fs` must also be passed to cheby1
.
Chebyshev type I filter order selection.
buttord
Find order and critical points from passband and stopband spec
cheby1
Filter design using order and critical points
iirdesign
General filter design using passband and stopband spec
iirfilter
General filter design using order and critical frequencies
Design a digital lowpass filter such that the passband is within 3 dB up to 0.2*(fs/2), while rejecting at least -40 dB above 0.3*(fs/2). Plot its frequency response, showing the passband and stopband constraints in gray.
>>> from scipy import signal
... import matplotlib.pyplot as plt
>>> N, Wn = signal.cheb1ord(0.2, 0.3, 3, 40)
... b, a = signal.cheby1(N, 3, Wn, 'low')
... w, h = signal.freqz(b, a)
... plt.semilogx(w / np.pi, 20 * np.log10(abs(h)))
... plt.title('Chebyshev I lowpass filter fit to constraints')
... plt.xlabel('Normalized frequency')
... plt.ylabel('Amplitude [dB]')
... plt.grid(which='both', axis='both')
... plt.fill([.01, 0.2, 0.2, .01], [-3, -3, -99, -99], '0.9', lw=0) # stop
... plt.fill([0.3, 0.3, 2, 2], [ 9, -40, -40, 9], '0.9', lw=0) # pass
... plt.axis([0.08, 1, -60, 3])
... plt.show()
The following pages refer to to this document either explicitly or contain code examples using this.
scipy.signal._filter_design.ellipord
scipy.signal._filter_design.iirfilter
scipy.signal._filter_design.cheb1ord
scipy.signal._filter_design.buttord
scipy.signal._filter_design.cheby1
scipy.signal._filter_design.cheb2ord
scipy.signal._filter_design.iirdesign
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