Continuous gravitational waves in the lab: recovering audio signals with a table-top optical microphone

TL;DR

This paper demonstrates how a table-top optical Michelson interferometer can recover audio signals, serving as an analog for gravitational wave detection and as an educational tool for teaching signal processing and physics concepts.

Contribution

It introduces a novel use of a Michelson interferometer as an optical microphone and applies gravitational-wave data analysis techniques to audio signal recovery in a lab setting.

Findings

Successfully recovered simple musical tones and speech signals.

Effective filtering techniques include notch plus Wiener filter and logMMSE estimator.

Demonstrates educational applications for physics and engineering students.

Abstract

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.