docs: def calculate_fft(data, tbin):
      """
      Function to calculate the Fourier transform of data.
      
      
      Parameters
      ----------
      data : numpy.ndarray
          1D or 2D array containing time series.
      tbin : float
          Bin size of time series (in ms).
      
      
      Returns
      -------
      freqs : numpy.ndarray
          Frequency axis of signal in Fourier space.         
      fft : numpy.ndarray
          Signal in Fourier space.
          
      """
      if len(np.shape(data)) > 1:
          n = len(data[0])
          return np.fft.fftfreq(n, tbin * 1e-3), np.fft.fft(data, axis=1)
      else:
          n = len(data)
          return np.fft.fftfreq(n, tbin * 1e-3), np.fft.fft(data)