zcy618 / biquad

Collection of alterable digital biquad filters for dynamic audio effect creation

Alterable biquad filters

This is a collection of digital biquad filters whose parameters f (frequency in Hz), g (gain in dB) and q (quality) can be varied at runtime. Following DF1 filter implementations are available:

• Allpass
• Bandpass
• Highpass
• Lowpass
• Highshelf
• Lowshelf
• Notch
• Peak

Basic usage

Filter with static configuration:

import biquad
import numpy as np

# load audio samples somehow
x, sr = np.zeros(...), 44100

# create a filter of your choice
f = biquad.bandpass(sr, f=sr/4, q=1)

# process all audio samples
y = f(x)

Filter with dynamic configuration:

import biquad
import numpy as np

# load audio samples somehow
x, sr = np.zeros(...), 44100

# create a filter of your choice
f = biquad.bandpass(sr)

# create parameter modifications as you like
myf = np.linspace(1, sr/4, len(x))
myq = np.linspace(2,  1/2, len(x))

# process all audio samples
y = f(x, f=myf, q=myq)

Keep in mind:

• All filters have a default value for the persistent parameters g and q, which is set in the particular __init__ method.
• Parameter f must be set either in the __init__ or in the __call__ method.
• The optional instantaneous parameters f, g and q, if specified in the __call__ method, override the persistent ones.

References

1. Cookbook formulae for audio EQ biquad filter coefficients by Robert Bristow-Johnson
2. Introduction to Digital Filters with Audio Applications by Julius O. Smith III

License

github.com/jurihock/biquad is licensed under the terms of the MIT license. For details please refer to the accompanying LICENSE file distributed with it.