  We compute the quasinormal mode frequencies and Regge poles of the canonical
acoustic hole (a black hole analogue), using three methods. First, we show how
damped oscillations arise by evolving generic perturbations in the time domain
using a simple finite-difference scheme. We use our results to estimate the
fundamental QN frequencies of the low multipolar modes $l=1, 2, \ldots$. Next,
we apply an asymptotic method to obtain an expansion for the frequency in
inverse powers of $l+1/2$ for low overtones. We test the expansion by comparing
against our time-domain results, and (existing) WKB results. The expansion
method is then extended to locate the Regge poles. Finally, to check the
expansion of Regge poles we compute the spectrum numerically by direct
integration in the frequency domain. We give a geometric interpretation of our
results and comment on experimental verification.
