A two-Gaussian model.

   This is simply the sum of two gaussian functions in some part of the
   spectrum. Each individual gaussian has its own peak frequency, sigma,
   and amp, but they share common offset and drift parameters.

def two_gaussian(freq, freq0_1, freq0_2, sigma1, sigma2, amp1, amp2,
                   offset, drift):
   """
   A two-Gaussian model.

   This is simply the sum of two gaussian functions in some part of the
   spectrum. Each individual gaussian has its own peak frequency, sigma,
   and amp, but they share common offset and drift parameters.

   """
   return (gaussian(freq, freq0_1, sigma1, amp1, offset, drift) +
           gaussian(freq, freq0_2, sigma2, amp2, offset, drift))