iir.py

#
# Author: Gabriel Galeote Checa
# MIT License
# IIR class implementation
#
import numpy as np

class IIR2_filter:
    """2nd order IIR filter"""

    def __init__(self,s):
        """Instantiates a 2nd order IIR filter
        s -- numerator and denominator coefficients
        """
        self.numerator0 = s[0]
        self.numerator1 = s[1]
        self.numerator2 = s[2]
        self.denominator1 = s[4]
        self.denominator2 = s[5]
        self.buffer1 = 0
        self.buffer2 = 0

    def filter(self,v):
        """Sample by sample filtering
        v -- scalar sample
        returns filtered sample
        """
        input = v - (self.denominator1 * self.buffer1) - (self.denominator2 * self.buffer2)
        output = (self.numerator1 * self.buffer1) + (self.numerator2 * self.buffer2) + input * self.numerator0
        self.buffer2 = self.buffer1
        self.buffer1 = input
        return output

class IIR_filter:
    """IIR filter"""
    def __init__(self,sos):
        """Instantiates an IIR filter of any order
        sos -- array of 2nd order IIR filter coefficients
        """
        self.cascade = []
        for s in sos:
            self.cascade.append(IIR2_filter(s))

    def filter(self,v):
        """Sample by sample filtering
        v -- scalar sample
        returns filtered sample
        """
        for f in self.cascade:
            v = f.filter(v)
        return v