`scipy.signal._filter_design:iirnotch`

source: build-install/usr/lib/python3.14/site-packages/scipy/signal/_filter_design.py:5436

Signature

def iirnotch(w0, Q, fs = 2.0, *, xp = None, device = None)

Summary

Design second-order IIR notch digital filter.

Extended Summary

A notch filter is a band-stop filter with a narrow bandwidth (high quality factor). It rejects a narrow frequency band and leaves the rest of the spectrum little changed.

Parameters

w0 : float: Frequency to remove from a signal. If fs is specified, this is in the same units as fs. By default, it is a normalized scalar that must satisfy 0 < w0 < 1, with w0 = 1 corresponding to half of the sampling frequency.
Q : float: Quality factor. Dimensionless parameter that characterizes notch filter -3 dB bandwidth bw relative to its center frequency, Q = w0/bw.
fs : float, optional: The sampling frequency of the digital system.
versionadded 1.2.0
xp : array_namespace, optional: Optional array namespace. Should be compatible with the array API standard, or supported by array-api-compat. Default: numpy
device : any: optional device specification for output. Should match one of the supported device specification in xp.

Returns

b, a : ndarray, ndarray: Numerator (b) and denominator (a) polynomials of the IIR filter.

Notes

Examples

Design and plot filter to remove the 60 Hz component from a signal sampled at 200 Hz, using a quality factor Q = 30

from scipy import signal
import matplotlib.pyplot as plt
import numpy as np

✓

fs = 200.0  # Sample frequency (Hz)
f0 = 60.0  # Frequency to be removed from signal (Hz)
Q = 30.0  # Quality factor
b, a = signal.iirnotch(f0, Q, fs)

✓

freq, h = signal.freqz(b, a, fs=fs)
fig, ax = plt.subplots(2, 1, figsize=(8, 6))

✓

ax[0].plot(freq, 20*np.log10(abs(h)), color='blue')
ax[0].set_title("Frequency Response")
ax[0].set_ylabel("Amplitude [dB]", color='blue')
ax[0].set_xlim([0, 100])
ax[0].set_ylim([-25, 10])

✗

(-25.0, 10.0)

ax[0].grid(True)

✓

ax[1].plot(freq, np.unwrap(np.angle(h))*180/np.pi, color='green')
ax[1].set_ylabel("Phase [deg]", color='green')
ax[1].set_xlabel("Frequency [Hz]")
ax[1].set_xlim([0, 100])
ax[1].set_yticks([-90, -60, -30, 0, 30, 60, 90])
ax[1].set_ylim([-90, 90])

✗

(-90.0, 90.0)

ax[1].grid(True)
plt.show()

✓

Aliases

scipy.signal.iirnotch