python-scipyHow can I use Python and SciPy to create a low pass filter?

In order to create a low pass filter using Python and SciPy, the following steps should be taken:

1. Import the necessary libraries:

import numpy as np
from scipy import signal

2. Create the low-pass filter. This can be done by using the signal.butter function, which takes three parameters:
   • N: The order of the filter
   • Wn: The cutoff frequency of the filter, normalized from 0 to 1 (1 being the Nyquist frequency)
   • btype: The type of filter, in this case ‘lowpass’

b, a = signal.butter(N=4, Wn=0.2, btype='lowpass')

3. Use the filter to filter a signal. This can be done by using the signal.lfilter function, which takes three parameters:
   • b: The numerator coefficient array of the filter
   • a: The denominator coefficient array of the filter
   • x: The signal to be filtered

x = np.linspace(0, 10, num=1000)
y = signal.lfilter(b, a, x)

4. Plot the filtered signal. This can be done by using the matplotlib.pyplot library:

import matplotlib.pyplot as plt

plt.plot(x, y)
plt.show()

Helpful links

• Scipy Signal Butter
• Scipy Signal Lfilter
• Matplotlib Pyplot

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