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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def gammatone(freq, bandwidth):
 """ ``A. Klapuri, "Multipich Analysis of Polyphonic Music and Speech Signals Using an Auditory Model". IEEE Transactions on Audio, Speech and Language Processing, vol. 16, no. 2, 2008, pp. 255-266.`` """

  bw = thub(bandwidth, 1)
  bw2 = thub(bw * 2, 4)
  freq = thub(freq, 4)
  resons = [resonator.z_exp, resonator.poles_exp] * 2
  return CascadeFilter(reson(freq, bw2) for reson in resons)