  Gravitational waves from coalescing binary black holes encode the evolution
of their spins prior to merger. In the post-Newtonian regime and on the
precession timescale, this evolution has one of three morphologies, with the
spins either librating around one of two fixed points ("resonances") or
circulating freely. In this work we perform full parameter estimation on
resonant binaries with fixed masses and spin magnitudes, changing three
parameters: a conserved "projected effective spin" $\xi$ and resonant family
$\Delta\Phi=0,\pi$ (which uniquely label the source), the inclination
$\theta_{JN}$ of the binary's total angular momentum with respect to the line
of sight (which determines the strength of precessional effects in the
waveform), and the signal amplitude. We demonstrate that resonances can be
distinguished for a wide range of binaries, except for highly symmetric
configurations where precessional effects are suppressed. Motivated by new
insight into double-spin evolution, we introduce new variables to characterize
precessing black hole binaries which naturally reflects the timescale
separation of the system and therefore better encode the dynamical information
carried by gravitational waves.
