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Fix issue in filter design code #13001

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Fix issue in filter design code #13001

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454be7e
Fix: updated filter code
ShubhamRaghu03 Sep 27, 2025
52670cf
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Sep 27, 2025
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140 changes: 30 additions & 110 deletions audio_filters/butterworth_filter.py
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Original file line number Diff line number Diff line change
@@ -1,6 +1,5 @@
from math import cos, sin, sqrt, tau

from audio_filters.iir_filter import IIRFilter

Check failure on line 2 in audio_filters/butterworth_filter.py

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Ruff (I001) 

audio_filters/butterworth_filter.py:1:1: I001 Import block is un-sorted or un-formatted

"""
Create 2nd-order IIR filters with Butterworth design.
Expand All @@ -10,27 +9,23 @@
"""


def make_lowpass(
frequency: int,
samplerate: int,
q_factor: float = 1 / sqrt(2),
) -> IIRFilter:
"""
Creates a low-pass filter

>>> filter = make_lowpass(1000, 48000)
>>> filter.a_coeffs + filter.b_coeffs # doctest: +NORMALIZE_WHITESPACE
[1.0922959556412573, -1.9828897227476208, 0.9077040443587427, 0.004277569313094809,
0.008555138626189618, 0.004277569313094809]
"""
def _precompute(frequency: int, samplerate: int, q_factor: float):
"""Helper to compute common values for filter design."""
w0 = tau * frequency / samplerate
_sin = sin(w0)
_cos = cos(w0)
alpha = _sin / (2 * q_factor)
return _sin, _cos, alpha


def make_lowpass(
frequency: int, samplerate: int, q_factor: float = 1 / sqrt(2)
) -> IIRFilter:
"""Creates a low-pass filter."""
_sin, _cos, alpha = _precompute(frequency, samplerate, q_factor)

b0 = (1 - _cos) / 2
b1 = 1 - _cos

a0 = 1 + alpha
a1 = -2 * _cos
a2 = 1 - alpha
Expand All @@ -41,26 +36,13 @@


def make_highpass(
frequency: int,
samplerate: int,
q_factor: float = 1 / sqrt(2),
frequency: int, samplerate: int, q_factor: float = 1 / sqrt(2)
) -> IIRFilter:
"""
Creates a high-pass filter

>>> filter = make_highpass(1000, 48000)
>>> filter.a_coeffs + filter.b_coeffs # doctest: +NORMALIZE_WHITESPACE
[1.0922959556412573, -1.9828897227476208, 0.9077040443587427, 0.9957224306869052,
-1.9914448613738105, 0.9957224306869052]
"""
w0 = tau * frequency / samplerate
_sin = sin(w0)
_cos = cos(w0)
alpha = _sin / (2 * q_factor)
"""Creates a high-pass filter."""
_sin, _cos, alpha = _precompute(frequency, samplerate, q_factor)

b0 = (1 + _cos) / 2
b1 = -1 - _cos

a0 = 1 + alpha
a1 = -2 * _cos
a2 = 1 - alpha
Expand All @@ -71,27 +53,14 @@


def make_bandpass(
frequency: int,
samplerate: int,
q_factor: float = 1 / sqrt(2),
frequency: int, samplerate: int, q_factor: float = 1 / sqrt(2)
) -> IIRFilter:
"""
Creates a band-pass filter

>>> filter = make_bandpass(1000, 48000)
>>> filter.a_coeffs + filter.b_coeffs # doctest: +NORMALIZE_WHITESPACE
[1.0922959556412573, -1.9828897227476208, 0.9077040443587427, 0.06526309611002579,
0, -0.06526309611002579]
"""
w0 = tau * frequency / samplerate
_sin = sin(w0)
_cos = cos(w0)
alpha = _sin / (2 * q_factor)
"""Creates a band-pass filter."""
_sin, _cos, alpha = _precompute(frequency, samplerate, q_factor)

b0 = _sin / 2
b1 = 0
b2 = -b0

a0 = 1 + alpha
a1 = -2 * _cos
a2 = 1 - alpha
Expand All @@ -102,22 +71,10 @@


def make_allpass(
frequency: int,
samplerate: int,
q_factor: float = 1 / sqrt(2),
frequency: int, samplerate: int, q_factor: float = 1 / sqrt(2)
) -> IIRFilter:
"""
Creates an all-pass filter

>>> filter = make_allpass(1000, 48000)
>>> filter.a_coeffs + filter.b_coeffs # doctest: +NORMALIZE_WHITESPACE
[1.0922959556412573, -1.9828897227476208, 0.9077040443587427, 0.9077040443587427,
-1.9828897227476208, 1.0922959556412573]
"""
w0 = tau * frequency / samplerate
_sin = sin(w0)
_cos = cos(w0)
alpha = _sin / (2 * q_factor)
"""Creates an all-pass filter."""
_sin, _cos, alpha = _precompute(frequency, samplerate, q_factor)

b0 = 1 - alpha
b1 = -2 * _cos
Expand All @@ -129,23 +86,10 @@


def make_peak(
frequency: int,
samplerate: int,
gain_db: float,
q_factor: float = 1 / sqrt(2),
frequency: int, samplerate: int, gain_db: float, q_factor: float = 1 / sqrt(2)
) -> IIRFilter:
"""
Creates a peak filter

>>> filter = make_peak(1000, 48000, 6)
>>> filter.a_coeffs + filter.b_coeffs # doctest: +NORMALIZE_WHITESPACE
[1.0653405327119334, -1.9828897227476208, 0.9346594672880666, 1.1303715025601122,
-1.9828897227476208, 0.8696284974398878]
"""
w0 = tau * frequency / samplerate
_sin = sin(w0)
_cos = cos(w0)
alpha = _sin / (2 * q_factor)
"""Creates a peak filter."""
_sin, _cos, alpha = _precompute(frequency, samplerate, q_factor)
big_a = 10 ** (gain_db / 40)

b0 = 1 + alpha * big_a
Expand All @@ -161,24 +105,12 @@


def make_lowshelf(
frequency: int,
samplerate: int,
gain_db: float,
q_factor: float = 1 / sqrt(2),
frequency: int, samplerate: int, gain_db: float, q_factor: float = 1 / sqrt(2)
) -> IIRFilter:
"""
Creates a low-shelf filter

>>> filter = make_lowshelf(1000, 48000, 6)
>>> filter.a_coeffs + filter.b_coeffs # doctest: +NORMALIZE_WHITESPACE
[3.0409336710888786, -5.608870992220748, 2.602157875636628, 3.139954022810743,
-5.591841778072785, 2.5201667380627257]
"""
w0 = tau * frequency / samplerate
_sin = sin(w0)
_cos = cos(w0)
alpha = _sin / (2 * q_factor)
"""Creates a low-shelf filter."""
_sin, _cos, alpha = _precompute(frequency, samplerate, 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
Expand All @@ -198,24 +130,12 @@


def make_highshelf(
frequency: int,
samplerate: int,
gain_db: float,
q_factor: float = 1 / sqrt(2),
frequency: int, samplerate: int, gain_db: float, q_factor: float = 1 / sqrt(2)
) -> IIRFilter:
"""
Creates a high-shelf filter

>>> 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]
"""
w0 = tau * frequency / samplerate
_sin = sin(w0)
_cos = cos(w0)
alpha = _sin / (2 * q_factor)
"""Creates a high-shelf filter."""
_sin, _cos, alpha = _precompute(frequency, samplerate, 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
Expand Down
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