IIR_filter.py

class IIR2Filter:
    def __init__(self,coefficients):    # need array of 6 elements input
        self.b0 = coefficients[0]
        self.b1 = coefficients[1]
        self.b2 = coefficients[2]
        self.a1 = coefficients[4]
        self.a2 = coefficients[5]
        self.acc = 0;        # accumulator
        self.b_x1 = 0;       # input x delay buffer
        self.b_x2 = 0;
        self.b_y1 = 0;       # output y delay buffer
        self.b_y2 = 0;
        
    def dofilter(self,x):
        self.acc = (x*self.b0) + (self.b_x1*self.b1) + (self.b_x2*self.b2) - (self.b_y1*self.a1) - (self.b_y2*self.a2)
        self.b_x2 = self.b_x1      # update delay lines
        self.b_x1 = x
        self.b_y2 = self.b_y1
        self.b_y1 = self.acc
        return self.acc

class IIRFilter:
    def __init__(self,coefficients_array):
        self.filters = []
        for i in range(len(coefficients_array)):
            self.filters.append(IIR2Filter(coefficients_array[i])) # instantiate 2nd order filters
                   
    def dofilter(self,u):
        for i in range(len(self.filters)):
           u = self.filters[i].dofilter(u)
        return u