diff --git a/lasp/filter/biquad.py b/lasp/filter/biquad.py new file mode 100644 index 0000000..41e6566 --- /dev/null +++ b/lasp/filter/biquad.py @@ -0,0 +1,43 @@ +#!/usr/bin/env python3 +# -*- coding: utf-8 -*- +"""! +Author: J.A. de Jong - ASCEE V.O.F. + +Description: Filter design implementation of common biquad filters that are +often used in parametric equalizers. +""" +__all__ = ['peaking', 'biquadTF'] +from scipy.signal import bilinear_zpk, zpk2sos, freqz_zpk, sosfreqz +from scipy.interpolate import interp1d +import numpy as np + +def peaking(fs, f0, Q, gain): + """ + Design of peaking biquad filter + + Args: + fs: Sampling frequency [Hz] + f0: Center frequency + Q: Quality factor (~ inverse of bandwidth) + gain: Increase in level at the center frequency + """ + A = np.sqrt(10**(gain/20)) + omg0 = 2*np.pi*f0/fs + alpha = np.sin(omg0)/Q/2 + b0 = 1+alpha*A + b1 = -2*np.cos(omg0) + b2 = 1-alpha*A + a0 = 1 + alpha/A + a1 = -2*np.cos(omg0) + a2 = 1-alpha/A + + return np.array([b0/a0, b1/a0, b2/a0, a0/a0, a1/a0, a2/a0]) + +def biquadTF(fs, freq, ba): + """ + Computes the transfer function of the biquad. + + """ + freq2, h = sosfreqz(ba, worN=48000, fs=fs) + interpolator = interp1d(freq2, h, kind='quadratic') + return interpolator(freq)