scipy.signal.buttord(wp, ws, gpass, gstop, analog=0)

Butterworth filter order selection.

Return the order of the lowest order digital Butterworth filter that loses no more than gpass dB in the passband and has at least gstop dB attenuation in the stopband.

Parameters :

wp, ws : float

Passband and stopband edge frequencies, normalized from 0 to 1 (1 corresponds to pi radians / 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]

gpass : float

The maximum loss in the passband (dB).

gstop : float

The minimum attenuation in the stopband (dB).

analog : int, optional

Non-zero to design an analog filter (in this case wp and ws are in radians / second).

Returns :

ord : int

The lowest order for a Butterworth filter which meets specs.

wn : ndarray or float

The Butterworth natural frequency (i.e. the “3dB frequency”). Should be used with butter to give filter results.

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