  Gravitational-wave observatories around the world are searching for
continuous waves: persistent signals from sources such as spinning neutron
stars. These searches use sophisticated statistical techniques to look for weak
signals in noisy data. In this paper, we demonstrate these techniques using a
table-top model gravitational-wave detector: a Michelson interferometer where
sound is used as an analog for gravitational waves. Using signal processing
techniques from continuous-wave searches, we demonstrate the recovery of tones
with constant and wandering frequencies. We also explore the use of the
interferometer as a teaching tool for educators in physics and electrical
engineering by using it as an "optical microphone" to capture music and speech.
A range of filtering techniques used to recover signals from noisy data are
detailed in the Supplementary Material. Here, we present highlights of our
results using a combined notch plus Wiener filter and the statistical log
minimum mean-square error (logMMSE) estimator. Using these techniques, we
easily recover recordings of simple chords and drums, but complex music and
speech are more challenging. This demonstration can be used by educators in
undergraduate laboratories and can be adapted for communicating
gravitational-wave and signal-processing topics to non-specialist audiences.
