code: def firwin_bpf(N_taps, f1, f2, fs = 1.0, pass_zero=False):
      
      return signal.firwin(N_taps,2*(f1,f2)/fs,pass_zero=pass_zero)
docs: Design a windowed FIR bandpass filter in terms of passband
      critical frequencies f1 < f2 in Hz relative to sampling rate
      fs in Hz. The number of taps must be provided.
  
      Mark Wickert October 2016