A colour with no standard behind it
White, pink and brown are defined by their slope. Green is not — there is no agreed specification, and every app that offers it has made its own. Honesty first: what you are hearing is this generator, not a category.
Measured here, it runs 25% below 250 Hz, 52% through the speech range, 23% above 4 kHz, centred at 3,494 Hz. That is the only description of it worth trusting, because the next site's green noise will measure differently.
The mistake: picking a colour by its reputation
Green noise arrives with a story attached — nature, calm, the middle of the spectrum. The story is marketing. What makes it useful is where its energy sits, and that half of it falls in the range where voices, televisions and kitchen sounds live.
If the thing waking you is a conversation through a wall, green noise has more to give than brown noise does. If it is a lorry, it has less. Pick by the disturbance and ignore the name.
Where it sits against the other three
Line the four colours up by spectral centre and green lands between pink at 2,511 Hz and white at 12,026 Hz, with brown far below at 537 Hz. In practice it is what you reach for when pink feels slightly thin and white is too sharp.
That is a narrow gap, and some people cannot hear it. If green and pink sound the same to you, use pink — it is better documented and behaves the same way overnight.
What this generator produces
Rendered on 2026-09-04 from the browser's own per-sample algorithm, 30 seconds at 48 kHz, measured with the EBU R128 meter and an averaged 8192-point FFT.
| Layer | Preset level | Loop | Loudness | RMS | Centre | Low / mid / high |
|---|---|---|---|---|---|---|
| Green Noise | 50% | generated, no loop | -15.9 LUFS | -16.7 dBFS | 3494 Hz | 25.2% / 52.2% / 22.6% |
- What this preset cannot do: These figures describe Slo's green noise only. Because no standard defines the colour, they say nothing about anyone else's, and comparing them across sites is meaningless.
Play green noise for sleep
- Open this page in any browser.
- The preset is already applied: green noise at 50%, timer set to all night.
- Press play, then open the pink noise preset in another tab and switch between them.
- Keep whichever one makes the room disappear faster.
Frequently asked questions
What is green noise?
A mid-weighted noise with no agreed definition. Slo's version measures 25% of its power below 250 Hz, 52% between 250 Hz and 4 kHz, and 23% above, centred at 3,494 Hz. Another app's green noise will differ.
Is green noise better than pink noise for sleep?
It sits slightly brighter — 3,494 Hz against pink's 2,511 Hz. That helps a little with voices and helps less with rumble. Many people cannot tell them apart, in which case use pink.
Can green noise play all night?
This preset is set to. Keep it quiet enough to hear an alarm and put the source away from your pillow.
Does green noise have health benefits?
No noise colour has demonstrated one. What green noise does is cover sound in the middle of the range. Anything beyond that is a claim without evidence behind it.
Is this a recording?
No. It is generated in the browser sample by sample, so there is no loop and no repeat.