scipy.signal.cheb1ord¶

scipy.signal.
cheb1ord
(wp, ws, gpass, gstop, analog=False, fs=None)[source]¶ Chebyshev type I filter order selection.
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.
 Parameters
 wp, wsfloat
Passband and stopband edge frequencies.
For digital filters, these are in the same units as fs. By default, fs is 2 halfcycles/sample, so these are normalized from 0 to 1, where 1 is the Nyquist frequency. (wp and ws are thus in halfcycles / 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, wp and ws are angular frequencies (e.g., rad/s).
 gpassfloat
The maximum loss in the passband (dB).
 gstopfloat
The minimum attenuation in the stopband (dB).
 analogbool, optional
When True, return an analog filter, otherwise a digital filter is returned.
 fsfloat, optional
The sampling frequency of the digital system.
New in version 1.2.0.
 Returns
See also
Examples
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()