I'm trying to convert my working 2nd-order Butterworth low pass filter to 1st-order in python, but it gives me very big numbers. Here's my 2nd-order Butterworth:
import math
import numpy as np
def bw_2nd(x=100, y, fc=200, fs=1000):
filtered_y = np.zeros(len(x))
omega_c = math.tan(np.pi*fc/fs)
k1 = np.sqrt(2)*omega_c
k2 = omega_c**2
a0 = k2/(1+k1+k2)
a1 = 2*a0
a2 = a0
k3 = 2*a0/k2
b1 = -(-2*a0+k3)
b2 = -(1-2*a0-k3)
filtered_y[0] = y[0]
filtered_y[1] = y[1]
for i in range(2, len(x)):
filtered_y[i] = np.int(a0*y[i]+a1*y[i-1]+a2*y[i-2]-(b1*filtered_y[i-1]+b2*filtered_y[i-2]))
return filtered_y
Here's my non-working 1st-order Butterworth:
def bw_1st(x=100, y, fc=200, fs=1000):
filtered_y = np.zeros(len(x))
omega_c = math.tan(np.pi*fc/fs)
k1 = np.sqrt(2)*omega_c
k2 = omega_c**2
a0 = k2/(1+k1+k2)
a1 = 2*a0
a2 = a0
k3 = 2*a0/k2
b1 = -(-2*a0+k3)
filtered_y[0] = y[0]
for i in range(1, len(x)):
filtered_y[i] = np.int(a0*y[i]+a1*y[i-1]-(b1*filtered_y[i-1]))
return filtered_y
... I removed all [i-2]s, which were a feed-forward and a feed-back. I thought it would work, but it doesn't. Could you tell me how to fix this? Thank you.
Both should be doing fine if you remove the np.int(...)
. I get no problems when calling it (after removing that).