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’), pole-zero (‘zpk’) or second order sections (‘sos’) form.

Parameters:

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 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, 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’), pole-zero (‘zpk’), or second-order 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 Second-order sections representation of the IIR filter. Only returned if `output=='sos'`.

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 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, 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’), pole-zero (‘zpk’), or second-order 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: Second-order sections representation of the IIR filter. Only returned if output=='sos'.

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