scipy.signal.iirdesign¶

scipy.signal.
iirdesign
(wp, ws, gpass, gstop, analog=False, ftype='ellip', output='ba')[source]¶ Complete IIR digital and analog filter design.
Given passband and stopband frequencies and gains, construct an analog or digital IIR filter of minimum order for a given basic type. Return the output in numerator, denominator (‘ba’), polezero (‘zpk’) or second order sections (‘sos’) form.
Parameters: wp, ws : float
Passband and stopband edge frequencies. For digital filters, these are normalized from 0 to 1, where 1 is the Nyquist frequency, pi radians/sample. (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).
gpass : float
The maximum loss in the passband (dB).
gstop : float
The minimum attenuation in the stopband (dB).
analog : bool, optional
When True, return an analog filter, otherwise a digital filter is returned.
ftype : str, optional
The type of IIR filter to design:
 Butterworth : ‘butter’
 Chebyshev I : ‘cheby1’
 Chebyshev II : ‘cheby2’
 Cauer/elliptic: ‘ellip’
 Bessel/Thomson: ‘bessel’
output : {‘ba’, ‘zpk’, ‘sos’}, optional
Type of output: numerator/denominator (‘ba’), polezero (‘zpk’), or secondorder sections (‘sos’). Default is ‘ba’.
Returns: b, a : ndarray, ndarray
Numerator (b) and denominator (a) polynomials of the IIR filter. Only returned if
output='ba'
.z, p, k : ndarray, ndarray, float
Zeros, poles, and system gain of the IIR filter transfer function. Only returned if
output='zpk'
.sos : ndarray
Secondorder sections representation of the IIR filter. Only returned if
output=='sos'
.See also
butter
 Filter design using order and critical points
buttord
 Find order and critical points from passband and stopband spec
iirfilter
 General filter design using order and critical frequencies
Notes
The
'sos'
output parameter was added in 0.16.0.