code: def highpass(cutoff):
    
    R = thub(exp(-cutoff), 2)
    G = (R + 1) / 2
    return G * (1 - z ** -1) / (1 - R * z ** -1)
docs: This strategy uses an exponential approximation for cut-off frequency
    calculation, found by matching the single pole and single zero Laplace
    highpass filter.