  The ability to perform high-precision optical measurements is paramount to
science and engineering. Laser interferometry enables interaction-free sensing
with a precision ultimately limited by shot noise. Quantum optical sensors can
surpass this limit, but single- or multi-photon schemes are challenged by low
experimental sampling rates, while squeezed-light approaches require complex
optical setups and sophisticated time gating. Here, we introduce a simple
method that infers optical phase shifts through standard intensity measurements
while still maintaining the quantum advantage in the measurement precision.
Capitalising on the robustness and high sampling rates of our device, we
implement a quantum optical microphone in the audio band. Its performance is
benchmarked against a classical laser microphone in a standardised
medically-approved speech recognition test on 45 subjects. We find that
quantum-recorded words improve the speech recognition threshold by $-0.57\,
\text{dB}_{\text{SPL}}$, thus making the quantum advantage audible. Not only do
these results open the door towards applications in quantum nonlinear
interferometry, but they also show that quantum phenomena can be experienced by
humans.
