code: def comb(delay, tau=inf):
    
    alpha = e ** (-delay / tau)
    return 1 / (1 - alpha * z ** -delay)
docs: Feedback comb filter for a given time constant (and delay).
  
      ``y[n] = x[n] + alpha * y[n - delay]``
  
    Parameters
    ----------
    delay :
      Feedback delay (lag), in number of samples.
    tau :
      Time decay (up to ``1/e``, or -8.686 dB), in number of samples, which
      allows finding ``alpha = e ** (-delay / tau)``. Defaults to ``inf``
      (infinite), which means alpha = 1.
  
    Returns
    -------
    A ZFilter instance with the comb filter.
  
    See Also
    --------
    freq2lag :
      Frequency (in rad/sample) to delay (in samples) converter.