Physics

The key insight is that frequency never changes when a wave crosses a boundary — it's determined by the source alone. What does change is the wavelength, since $v = f\lambda$ and velocity differs between media. So you'll hear the same 600 Hz in air as was emitted in water; the sound doesn't "become" a different frequency just because it travels through a different material. This is why a siren sounds the same pitch whether you're in water or air.

The key insight is that frequency never changes when a wave crosses a boundary — it's determined by the source alone. What does change is the wavelength, since $v = f\lambda$ and velocity differs between media. So you'll hear the same 600 Hz in air as was emitted in water; the sound doesn't "become" a different frequency just because it travels through a different material. This is why a siren sounds the same pitch whether you're in water or air.