  The bias energies of various two-level systems (TLSs) and their strengths of
interactions with the strain are calculated for Ar:N$_2$ glass. Unlike the case
in KBr:CN, a distinct class of TLSs having weak interaction with the strain and
untypically small bias energies is not found. The addition of CO molecules
introduces CO flips which form such a class of weakly interacting TLSs, albeit
at much lower coupling than are typically observed in solids. We conclude that
because of the absence of a distinct class of weakly interacting TLSs, Ar:N$_2$
is a non-universal glass, the first such system in three dimensions and in
ambient pressure. Our results further suggest that Ar:N$_2$:CO may show
universal properties, but at temperatures lower than $\approx 0.1$ K, much
smaller than typical temperature $\approx 3$ K associated with universality,
because of the untypical softness of this system. Our results thus shed light
on two long standing questions regarding low temperature properties of glasses:
the necessary and sufficient conditions for quantitative universality of phonon
attenuation, and what dictates the energy scale of $\approx 3$ K below which
universality it typically observed.
