Grey noise

Noise shaped to sound equally loud at every pitch, the way your ear hears it.

Our ears are most sensitive around 2–5 kHz and much less sensitive to deep bass. Grey noise compensates: it follows the inverse of the ear’s sensitivity curve (A-weighting, the standard approximation), with more bass and slightly less upper midrange than white noise. Here the bass boost is capped at 20 dB, below about 95 Hz.

The result sounds flatter and fuller than white noise, somewhere between pink and white. Which color is most comfortable is personal; it is worth trying each one.

Using it for a baby? Keep the phone across the room, not in the crib, at a low volume (why).