code: def get_filter_gain(b, a, f_gain, fs):
      
      # Save the passband gain
      w, h = signal.freqz(b, a)
      w_gain = f_gain * 2 * np.pi / fs
  
      ind = np.where(w >= w_gain)[0][0]
      gain = abs(h[ind])
  
      return gain
docs: Given filter coefficients, return the gain at a particular
      frequency.
  
      Parameters
      ----------
      b : list
          List of linear filter b coefficients
      a : list
          List of linear filter a coefficients
      f_gain : int or float, optional
          The frequency at which to calculate the gain
      fs : int or float, optional
          The sampling frequency of the system