code: def freqz_cas(sos,w):
      
      Ns,Mcol = sos.shape
      w,Hcas = signal.freqz(sos[0,:3],sos[0,3:],w)
      for k in range(1,Ns):
          w,Htemp = signal.freqz(sos[k,:3],sos[k,3:],w)
          Hcas *= Htemp
      return w, Hcas
docs: Cascade frequency response
      
      Mark Wickert October 2016