docs: def combine_with_wd_noise(f_n, amp_n, f_n_wd, amp_n_wd):
      """Combine noise with wd noise.
  
      Combines noise and white dwarf background noise based on greater
      amplitude value at each noise curve step.
  
      Args:
          f_n (float array): Frequencies of noise curve.
          amp_n (float array): Amplitude values of noise curve.
          f_n_wd (float array): Frequencies of wd noise.
          amp_n_wd (float array): Amplitude values of wd noise.
  
      Returns:
          (tuple of float arrays): Amplitude values of combined noise curve.
  
      """
  
      # interpolate wd noise
      amp_n_wd_interp = interpolate.interp1d(f_n_wd, amp_n_wd, bounds_error=False, fill_value=1e-30)
  
      # find points of wd noise amplitude at noise curve frequencies
      amp_n_wd = amp_n_wd_interp(f_n)
  
      # keep the greater value at each frequency
      amp_n = amp_n*(amp_n >= amp_n_wd) + amp_n_wd*(amp_n < amp_n_wd)
      return f_n, amp_n