text: """
  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)
  