bundles / scipy latest / scipy / signal / _filter_design / cheb2ord
function
scipy.signal._filter_design:cheb2ord
Signature
def cheb2ord ( wp , ws , gpass , gstop , analog = False , fs = None ) Summary
Chebyshev type II filter order selection.
Extended Summary
Return the order of the lowest order digital or analog Chebyshev Type II filter that loses no more than gpass dB in the passband and has at least gstop dB attenuation in the stopband.
Parameters
wp, ws: floatPassband and stopband edge frequencies.
For digital filters, these are in the same units as
fs. By default,fsis 2 half-cycles/sample, so these are normalized from 0 to 1, where 1 is the Nyquist frequency. (wpandwsare 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,
wpandwsare angular frequencies (e.g., rad/s).gpass: floatThe maximum loss in the passband (dB).
gstop: floatThe minimum attenuation in the stopband (dB).
analog: bool, optionalWhen True, return an analog filter, otherwise a digital filter is returned.
fs: float, optionalThe sampling frequency of the digital system.
Returns
Notes
Array API Standard Support
cheb2ord has experimental support for Python Array API Standard compatible backends in addition to NumPy. Please consider testing these features by setting an environment variable SCIPY_ARRAY_API=1 and providing CuPy, PyTorch, JAX, or Dask arrays as array arguments. The following combinations of backend and device (or other capability) are supported.
==================== ==================== ==================== Library CPU GPU ==================== ==================== ==================== NumPy ✅ n/a CuPy n/a ✅ PyTorch ✅ ✅ JAX ⚠️ no JIT ⛔ Dask ⚠️ computes graph n/a ==================== ==================== ====================
The torch backend on GPU does not support the case where wp and ws specify a Bandstop filter.
See
dev-arrayapifor more information.
Examples
Design a digital bandstop filter which rejects -60 dB from 0.2*(fs/2) to 0.5*(fs/2), while staying within 3 dB below 0.1*(fs/2) or above 0.6*(fs/2). Plot its frequency response, showing the passband and stopband constraints in gray.from scipy import signal import matplotlib.pyplot as plt import numpy as np✓
N, Wn = signal.cheb2ord([0.1, 0.6], [0.2, 0.5], 3, 60) b, a = signal.cheby2(N, 60, Wn, 'stop') w, h = signal.freqz(b, a)✓
plt.semilogx(w / np.pi, 20 * np.log10(abs(h))) plt.title('Chebyshev II bandstop filter fit to constraints') plt.xlabel('Normalized frequency') plt.ylabel('Amplitude [dB]')✗
plt.grid(which='both', axis='both')
✓plt.fill([.01, .1, .1, .01], [-3, -3, -99, -99], '0.9', lw=0) # stop plt.fill([.2, .2, .5, .5], [ 9, -60, -60, 9], '0.9', lw=0) # pass plt.fill([.6, .6, 2, 2], [-99, -3, -3, -99], '0.9', lw=0) # stop plt.axis([0.06, 1, -80, 3])✗
plt.show()
✓
See also
Aliases
-
scipy.signal.cheb2ord