Quick Answer: Grey noise is white noise filtered through an inverse Fletcher-Munson equal-loudness curve, so all frequencies are perceived as equally loud to human hearing. Unlike white noise (which sounds harsh because our ears are more sensitive to mid-high frequencies), grey noise sounds perceptually flat and comfortable. It is the most precisely engineered noise colour for human auditory comfort and is particularly useful for people who find white noise too shrill for sleep.
In This Guide
Reading Time: 8 minutes
Most people who discover grey noise do so after being unsatisfied with white noise. They tried white noise for sleep and found it too bright, too hissy, or fatiguing to listen to over a full night. They may have shifted to pink or brown noise with better results. Grey noise sits at the end of that progression: it is the noise colour that was built from a model of how human hearing actually works, rather than from a simple spectral formula.
That basis makes it worth understanding, because the same property that makes it comfortable also makes it the more effective masking tool for specific types of sleepers.
What Grey Noise Actually Is
To understand grey noise, start with white noise. White noise contains equal energy at every frequency across the audible spectrum, from 20 Hz to 20,000 Hz. If you plotted the energy at each frequency, you would see a flat horizontal line.
This spectral flatness sounds like a simple, democratic distribution of sound. The problem is that human hearing is not flat. The ear's sensitivity varies considerably across the frequency range, with peak sensitivity in the 2,000 to 5,000 Hz range and significantly reduced sensitivity at the low and high extremes. So when you listen to spectrally flat white noise, you perceive the mid-range frequencies much more loudly than the lows and highs. White noise sounds harsh and hissy to most people because of this perceptual imbalance.
Pink noise compensates partially by reducing energy at higher frequencies at a rate of 3 decibels per octave. This produces the gentler "rainfall" quality that many people find more comfortable. Brown noise compensates more aggressively, producing the deep rumbling bass quality that has become popular for sleep and focus.
Grey noise takes the compensation further and makes it precise. It is white noise filtered through an inverse equal-loudness contour: the filter reduces energy exactly where the ear is sensitive and boosts it where the ear is less sensitive. The result is a perceptually flat sound, one where all frequency bands are heard as equally present rather than weighted toward the mid-range.
The Fletcher-Munson Basis
The equal-loudness contours used to create grey noise originated with research by Harvey Fletcher and Wilden A. Munson published in 1933, which mapped how loud a pure tone at each frequency must be to appear equally loud as a 1,000 Hz reference tone at various volume levels. Their curves showed that the human ear is most sensitive around 3,000-4,000 Hz and progressively less sensitive toward both the low bass and the highest treble.
Why the Curves Matter for Noise Colour
When you apply the inverse of the Fletcher-Munson curves to white noise, you subtract energy where the ear is most sensitive and add it where the ear is least sensitive. The result is a broadband noise signal that stimulates the auditory system uniformly rather than emphasising the frequency range where the ear is already most alert. For sleep use, this uniformity matters because a signal that is perceptually flat is less fatiguing to listen to over extended periods. The mid-range frequencies that white noise emphasises are also the frequencies most associated with speech intelligibility, which is part of why white noise can feel stimulating rather than relaxing for some people.
Modern ISO standard 226:2003 updated the equal-loudness contours with more precise measurements than Fletcher and Munson's original work. App developers creating grey noise generators typically use these updated curves, which is why grey noise from a well-calibrated generator will differ slightly from older formulations.
Grey vs White, Pink, and Brown Noise
Noise Colours Compared for Sleep Use
| Noise Colour | Spectral Shape | Perceived Quality | Best For |
|---|---|---|---|
| White | Flat (equal energy/Hz) | Harsh, hissy | General masking, office environments |
| Pink | -3 dB/octave rolloff | Gentler, rain-like | Sleep, relaxation, mild masking |
| Brown | -6 dB/octave rolloff | Deep, bass-heavy | Deep focus, strong masking, rumble preference |
| Grey | Inverse equal-loudness contour | Perceptually flat, comfortable | Auditory comfort, tinnitus, sensitive listeners |
The practical distinction most useful for sleep decisions: white noise is the strongest masker by energy but the harshest to listen to; brown noise is the gentlest to listen to and the warmest sounding; pink noise sits between them; grey noise is the most perceptually comfortable across the full frequency range, which makes it suitable for longer listening periods without auditory fatigue.
Why Grey Noise Works for Sleep
All coloured noise types improve sleep primarily through auditory masking: the broadband sound reduces the contrast between silence and sudden disruptive sounds (a door slamming, a car on the street, a partner shifting) that cause micro-arousals during light sleep stages. Research on noise masking and sleep published in the Journal of Theoretical Biology and referenced in sleep medicine literature confirms that masking sudden sounds reduces sleep fragmentation.
Grey noise's advantage over white noise for this purpose is comfort during use rather than masking efficiency. At the same volume level, white and grey noise provide similar masking effectiveness, but grey noise is more sustainable to listen to for a full night because it does not emphasise the fatiguing mid-range frequencies. For people who have tried white noise and abandoned it due to the harsh quality, grey noise is worth trying before concluding that noise masking does not work for them.
Volume Guidelines for Sleep Noise
Research consistently suggests sleep masking noise should sit at 40-50 decibels, roughly equivalent to a quiet conversation in the next room. Above 65 dB, background noise can itself disrupt sleep quality, and extended exposure above 55 dB contributes to auditory fatigue. A simple check: if you need to raise your voice to speak to a partner in the same room, the volume is too high. Most sleep apps default to higher volumes than necessary. Lower is more effective for sustained overnight use than the instinct to "drown out" disturbances would suggest.
Who Benefits Most from Grey Noise
Grey noise is specifically useful for three groups:
People who find white noise harsh. If you have tried white noise for sleep and found it fatiguing, shrill, or difficult to relax with, the issue is the perceptual mid-range emphasis. Grey noise corrects this. For these listeners, grey noise typically feels immediately more comfortable without the need for extended adjustment.
Tinnitus sufferers. People with tinnitus use background sound to reduce the perceptual contrast between the tinnitus tone and ambient silence. Grey noise provides broadband sound enrichment across all frequencies, including the specific frequencies where tinnitus often presents (typically 3,000-8,000 Hz), in a spectrally comfortable way. It does not mask tinnitus completely but reduces the annoyance by providing auditory context. Clinical tinnitus sound therapy should be directed by an audiologist.
Detail-oriented listeners and musicians. People with careful ears, trained or naturally discerning, often find white noise's spectral imbalance distracting in a way that general listeners may not notice. The perceptual flatness of grey noise removes this distraction.
Grey Noise and Tinnitus
Tinnitus affects roughly 15% of Canadians, with rates higher among adults over 50 and those with occupational noise exposure histories. Many people with tinnitus use sleep noise apps specifically to manage the tinnitus perception that becomes more prominent in quiet environments.
Research published in the Journal of Speech, Language, and Hearing Research (2022) on sound therapy duration found that daily sound therapy improved tinnitus relief outcomes, with the mixing-point approach (sound slightly quieter than, or at, the tinnitus perception level) producing better habituation outcomes than complete masking. Grey noise is well-suited to the mixing-point approach because its broadband, perceptually comfortable quality makes it easier to maintain at low volumes without the harsh quality that causes people to either turn white noise up to suppressing levels or turn it off entirely.
A Note on Tinnitus and Sleep Quality
Tinnitus is a significant contributor to sleep difficulty for many people, and it is underdiagnosed as a sleep disruptor. If you are using sleep noise apps and finding limited benefit, it is worth ruling out tinnitus as a contributing factor with an audiologist. Sound therapy for tinnitus and sound therapy for general sleep masking are related but distinct approaches, and the guidance for tinnitus management should come from a hearing health professional.
Apps and Sources for Grey Noise
Grey noise is less widely available than white, pink, or brown noise but accessible with a little searching:
myNoise (mynoise.net). One of the most customisable sound generators available, with a dedicated grey noise generator whose frequency bands can be adjusted individually. Free to use with optional donation. Available as a web app and as a paid iOS/Android app.
Relax Melodies and White Noise+. Both include grey noise among their noise colour options. These apps have sleep timer functionality, which matters for the recommendation to stop playback after 45-60 minutes rather than running through the night.
Tinnitus Relief apps. Apps including ReSound Tinnitus Relief and Tinnitus Masker include grey noise alongside other sound therapy options specifically because of its tinnitus management properties.
Streaming platforms. Spotify and Apple Music carry grey noise tracks under "sleep sounds" and "focus" playlists. Quality varies depending on the creator. Look for tracks that describe their basis as equal-loudness-weighted or Fletcher-Munson filtered for the most precisely engineered versions.
Frequently Asked Questions
What is grey noise?
Grey noise is white noise that has been filtered through an inverse equal-loudness contour, such as the Fletcher-Munson curves, so that all frequencies are perceived as equally loud by the average human listener. Because human hearing is more sensitive to mid-range frequencies (2,000-5,000 Hz) than to low or high extremes, grey noise reduces energy in the mid-range and boosts it at the extremes to compensate. The result is a perceptually flat, comfortable sound.
Is grey noise better for sleep than white noise?
For people who find white noise harsh or uncomfortably bright-sounding, grey noise is typically more comfortable for extended sleep use. The perceptually flat quality provides broadband auditory masking without the fatiguing effect of white noise's emphasis in the frequency range where human hearing is most sensitive. For people who do not find white noise harsh, the practical difference is small.
What is grey noise good for?
Grey noise is particularly useful for people who find white noise too harsh, people with tinnitus who need broadband masking sound that does not fatigue the auditory system during sleep, and listeners with detailed hearing who notice the perceptual imbalance of white noise. For general sleep masking in a noisy environment, pink or brown noise often works equally well for most people.
What apps have grey noise?
myNoise (mynoise.net) is the most frequently cited platform for grey noise, offering a calibrated generator with adjustable frequency bands. Relax Melodies, White Noise+, and several tinnitus-focused apps including Tinnitus Relief also include grey noise. Spotify and Apple Music carry grey noise tracks in sleep playlists. Search for "grey noise" or "equal-loudness noise" in app stores.
Can grey noise help with tinnitus?
Grey noise is used in tinnitus sound therapy because it provides broadband enrichment across all audible frequencies in a perceptually comfortable way. The goal in tinnitus management is sound enrichment at a mixing point, where background sound and tinnitus perception are at a similar level. Grey noise achieves this with less auditory fatigue than white noise for many people. Clinical guidance on tinnitus sound therapy should come from an audiologist.
Sources
- Fletcher, H., Munson, W.A. "Loudness, its definition, measurement and calculation." Journal of the Acoustical Society of America 5(2):82-108 (1933).
- ISO 226:2003. "Acoustics, Normal equal-loudness-level contours." International Organization for Standardization, Geneva, 2003.
- Stacey, P.C., Fortnum, H.M., Barton, G.R., Summerfield, A.Q. "Hearing-impaired children in the United Kingdom." Ear Hear 27(4):359-374 (2006). (Auditory sensitivity variation).
- Henry, J.A., et al. "The impact of daily hours of sound therapy on tinnitus relief for people with chronic tinnitus." Journal of Speech, Language, and Hearing Research 65(12):4514-4528 (2022).
Related Reading:
- White, Pink, and Brown Noise for Sleep
- Binaural Beats for Sleep
- Smart Bedroom Lighting for Sleep
- Best Mattress for Insomnia
- Creating a Better Sleep Environment
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