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The sound of a waterfall or a river flowing is repetitive and steady; a noise we’d tune out while awake.
But when it comes to bedtime, it can help relax the body because we perceive it as a non-threatening sound — meaning we let our guard down when we hear it.
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If white noise doesn’t work for you, a slightly different ambient sound called pink noise might be effective.
However, like white noise, researchers still lack hard data to understand its effectiveness — or lack thereof.