Dark noise

Deeper and softer than brown noise: a low rumble with almost no hiss.

There is no standard definition of dark noise. Here it is brown noise with the treble rolled off further: above about 400 Hz the level falls 18 dB per octave instead of 6. It sounds like a distant engine, or wind heard through a closed window.

Because almost nothing is left in the upper range, it doesn’t mask voices or sharp sounds as well as pink or white noise. Many people find it the easiest to listen to for hours, which is why it is popular for sleep.

On a small phone speaker much of it is below what the speaker can play. Headphones, or a Bluetooth speaker with some bass, make a big difference.

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