Errr.. not so. It is completely digital (hope I understood you properly..).
The idea is to take the standard astro image of the star through the diffraction grating (or prism), with all standard techniques to improve S/N, using DSS
http://deepskystacker.free.fr/english/index.html
Then, the spectrum post processing was done using Iris:
http://www.astrosurf.com/buil/us/iris/iris.htm