Audio Filtering is necessary when you need to remove or reduce the unwanted part of a sound.

• Remove unwanted noise
  • Example: Hiss from a microphone recording (usually high frequencies).
  • Solution: Apply a low-pass filter to cut out high-frequency noise.
• Reduce rumble or hum
  • Example: Background hum at 50/60 Hz from electrical equipment.
  • Solution: Apply a high-pass filter to remove low-frequency rumble.
• Isolate specific frequency bands
  • Example: Extract the vocals from a song (human voice ≈ 300–3400 Hz).
  • Solution: Apply a band-pass filter that keeps only that range.
• Suppress a single annoying frequency
  • Example: Feedback whistle at 1000 Hz during live sound.
  • Solution: Apply a notch filter at 1000 Hz to reduce it.
• Improve clarity
  • Example: In speech enhancement, filters reduce background noise so words are clearer.

Common Types of Filters

• Low-Pass Filter (LPF) → keeps low frequencies, removes high ones.
• High-Pass Filter (HPF) → keeps high frequencies, removes low ones.
• Band-Pass Filter (BPF) → keeps a middle range, removes low and high.
• Band-Stop (Notch) Filter → removes a specific narrow range, keeps others.

Import the pydub, scipy, and numpy library:

from pydub import AudioSegment
from pydub.generators import Sine, Square, WhiteNoise
from pydub.playback import play
import numpy as np
import matplotlib.pyplot as plt
from scipy.signal import butter, lfilter

Filtering with pydub since it has built-in low-pass and high-pass filters:

low_passed = combined.low_pass_filter(1000)   # Cut above 1kHz
high_passed = combined.high_pass_filter(1000) # Cut below 1kHz
print("Playing low-pass filtered...")
play(low_passed)
print("Playing high-pass filtered...")
play(high_passed)

Output:

Playing low-pass filtered...
Input #0, wav, from '/var/folders/gc/49grx5f90nv3f12yh4jhhf740000gn/T/tmp128b0_oy.wav':
  Duration: 00:00:06.00, bitrate: 705 kb/s
  Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, 1 channels, s16, 705 kb/s
   5.91 M-A:  0.000 fd=   0 aq=    0KB vq=    0KB sq=    0B 

Playing high-pass filtered...
Input #0, wav, from '/var/folders/gc/49grx5f90nv3f12yh4jhhf740000gn/T/tmpn9swuzo6.wav':
  Duration: 00:00:06.00, bitrate: 705 kb/s
  Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, 1 channels, s16, 705 kb/s
   5.88 M-A:  0.000 fd=   0 aq=    0KB vq=    0KB sq=    0B