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"""
This module provides scipy versions of high_pass_filter, and low_pass_filter
as well as an additional band_pass_filter.
Of course, you will need to install scipy for these to work.
When this module is imported the high and low pass filters from this module
will be used when calling audio_segment.high_pass_filter() and
audio_segment.high_pass_filter() instead of the slower, less powerful versions
provided by pydub.effects.
"""
from scipy.signal import butter, sosfilt
from .utils import register_pydub_effect
def _mk_butter_filter(freq, type, order):
"""
Args:
freq: The cutoff frequency for highpass and lowpass filters. For
band filters, a list of [low_cutoff, high_cutoff]
type: "lowpass", "highpass", or "band"
order: nth order butterworth filter (default: 5th order). The
attenuation is -6dB/octave beyond the cutoff frequency (for 1st
order). A Higher order filter will have more attenuation, each level
adding an additional -6dB (so a 3rd order butterworth filter would
be -18dB/octave).
Returns:
function which can filter a mono audio segment
"""
def filter_fn(seg):
assert seg.channels == 1
nyq = 0.5 * seg.frame_rate
try:
freqs = [f / nyq for f in freq]
except TypeError:
freqs = freq / nyq
sos = butter(order, freqs, btype=type, output='sos')
y = sosfilt(sos, seg.get_array_of_samples())
return seg._spawn(y.astype(seg.array_type))
return filter_fn
@register_pydub_effect
def band_pass_filter(seg, low_cutoff_freq, high_cutoff_freq, order=5):
filter_fn = _mk_butter_filter([low_cutoff_freq, high_cutoff_freq], 'band', order=order)
return seg.apply_mono_filter_to_each_channel(filter_fn)
@register_pydub_effect
def high_pass_filter(seg, cutoff_freq, order=5):
filter_fn = _mk_butter_filter(cutoff_freq, 'highpass', order=order)
return seg.apply_mono_filter_to_each_channel(filter_fn)
@register_pydub_effect
def low_pass_filter(seg, cutoff_freq, order=5):
filter_fn = _mk_butter_filter(cutoff_freq, 'lowpass', order=order)
return seg.apply_mono_filter_to_each_channel(filter_fn)
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