Rock concerts can be load, but here we just played At the hundredth meridian (by the Tragically Hip) quietly on a piezo transducer, and picked up its vibrations using a fiber sensor. The strain on the fiber sensor was recorded through a 75 km fiber optic cable - no amplifiers, no boosters - using a diode laser that was locked to the strain sensor’s resonance wavelength. The very long-haul transmission was possible because we heterodyned the return signal using a local oscillator. The signal-to-noise increased as expected - just as that for FM radio is better than AM radio.

Applications for the technique are in long-range recordings of sound and infrasound in hostile environments such as the ocean floor, active geological areas, or industrial plants.

Read about their research in:
A. G. Santos, S. Daxini, J. A. Barnes, X. Gu and H. -P. Loock, "Fiber Strain Sensing at Over 75 km Distance Using the Coherently Amplified Pound-Drever-Hall Method," in Journal of Lightwave Technology
https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=11614399