  We use the well tested StarTrack binary population synthesis code to examine
the properties of the population of compact object binaries. We calculate the
distribution of masses and mass ratios taking into account weights introduced
by observability in gravitational waves during inspiral. We find that in the
observability weighted distribution of double neutron star binaries there are
two peaks: one for nearly equal mass systems, and one for the systems
consisting of a low and a high mass neutron star, $q=0.6-0.7$. The
observability weighted distribution of black hole neutron star binaries is
concentrated on the systems with the mass ratio $q=0.3-0.5$, while for the
double black hole binaries the observability weighted distribution is dominated
by the massive, nearly equal mass binaries with $q>0.7$.
