  MATISSE (Multi AperTure mid-Infrared SpectroScopic Experiment) is the next
generation spectro-interferometer at the European Southern Observatory VLTI
operating in the spectral bands L, M and N, and combining four beams from the
unit and auxiliary telescopes. MATISSE is now fully integrated at the
Observatoire de la C\^ote d'Azur in Nice (France), and has entered very
recently its testing phase in laboratory. This paper summarizes the equations
describing the MATISSE signal and the associated sources of noise. The
specifications and the expected performances of the instrument are then
evaluated taking into account the current characteristics of the instrument and
the VLTI infrastructure, including transmission and contrast degradation
budgets. In addition, we present the different MATISSE simulation tools that
will be made available to the future users.
