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Update butterworth_filter.py

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Aryan Rajesh 2024-11-04 10:45:17 +05:30 committed by GitHub
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1 changed files with 18 additions and 15 deletions
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audio_filters/butterworth_filter.py
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@ -1,15 +1,13 @@
from math import cos, sin, sqrt, tau
from audio_filters.iir_filter import IIRFilter
"""
Create 2nd-order IIR filters with Butterworth design.
Code based on https://webaudio.github.io/Audio-EQ-Cookbook/audio-eq-cookbook.html
Alternatively you can use scipy.signal.butter, which should yield the same results.
Alternatively, you can use scipy.signal.butter, which should yield the same results.
"""
def make_lowpass(
frequency: int,
samplerate: int,
@ -208,27 +206,32 @@ def make_highshelf(
>>> filter = make_highshelf(1000, 48000, 6)
>>> filter.a_coeffs + filter.b_coeffs # doctest: +NORMALIZE_WHITESPACE
[2.2229172136088806, -3.9587208137297303, 1.7841414181566304, 4.295432981120543,
-7.922740859457287, 3.6756456963725253]
[2.2229172136088806, -3.616080374557819, 1.4122939941901636, 0.5690651073937642,
-1.3335115824061685, 0.7666141956641752]
"""
w0 = tau * frequency / samplerate
_sin = sin(w0)
_cos = cos(w0)
alpha = _sin / (2 * q_factor)
big_a = 10 ** (gain_db / 40)
pmc = (big_a + 1) - (big_a - 1) * _cos
ppmc = (big_a + 1) + (big_a - 1) * _cos
mpc = (big_a - 1) - (big_a + 1) * _cos
pmpc = (big_a - 1) + (big_a + 1) * _cos
pmc = (big_a + 1) + (big_a - 1) * _cos
ppmc = (big_a + 1) - (big_a - 1) * _cos
mpc = (big_a - 1) + (big_a + 1) * _cos
pmpc = (big_a - 1) - (big_a + 1) * _cos
aa2 = 2 * sqrt(big_a) * alpha
b0 = big_a * (ppmc + aa2)
b1 = -2 * big_a * pmpc
b2 = big_a * (ppmc - aa2)
a0 = pmc + aa2
a1 = 2 * mpc
a2 = pmc - aa2
b0 = big_a * (pmc - aa2)
b1 = -2 * big_a * mpc
b2 = big_a * (pmc + aa2)
a0 = ppmc - aa2
a1 = 2 * pmpc
a2 = ppmc + aa2
filt = IIRFilter(2)
filt.set_coefficients([a0, a1, a2], [b0, b1, b2])
return filt
if __name__ == "__main__":
import doctest
doctest.testmod()