Sound Masking

Masking does not make a sound quieter. It makes the sound stop standing out, which is a different operation with different rules — and the main rule is that the colour has to match.

Masking Is Not Blocking, and the Difference Decides Everything

There are exactly two ways to stop being bothered by a sound, and almost every disappointment in this area comes from using one while expecting the other.

Blocking reduces what arrives. Heavier glazing, a solid door, a seal along the bottom of it, earplugs. Less acoustic energy reaches your ear than before. This is the intuitive approach, it is the one people try first, and it is expensive, effortful, and least effective exactly where household noise is worst — at low frequencies, which pass through walls, floors and windows far more readily than high ones.

Masking raises everything else. The intrusion arrives unchanged. What changes is the background it arrives into, which you deliberately make louder. The room ends up carrying more acoustic energy than it did before, not less, and yet the sound you cared about stops registering.

That is a genuinely strange trade, and stated plainly it sounds like a trick. It is not. It works because of how hearing decides what counts as an event.

The Ear Compares, It Does Not Measure

A sound meter reports absolute level. Hearing does not work that way. What reaches awareness — and what wakes you — is closer to a contrast judgement: how far does this sound rise above what was already there?

A floorboard creak of a given loudness in a silent room is an event. The identical creak in a room with a steady background at the same level is nothing at all. Nothing about the creak changed. What changed is that it no longer stands out from its surroundings, and the auditory system, which is built to detect changes rather than to log levels, has nothing to report.

This is why masking works at all, and it is also why the second rule below exists. Detection is not settled across the whole of hearing at once. It is settled within narrow frequency regions, one at a time, and only sound inside the same region takes part in the comparison.

Masking Is Local to Frequency, Which Is Why Colour Matters

The inner ear behaves like a bank of overlapping filters. Each place along it responds to a narrow band of frequencies, and the comparison that decides whether you notice something happens inside those bands rather than across the whole spectrum.

The consequence is direct and it is the single most useful thing on this page. Only the part of your masking sound that shares a frequency region with the intrusion does any work. Everything else is not helping. It is not neutral either — it is extra loudness in the room, extra sound you are exposed to all night, buying nothing.

Play white noise at a lorry passing outside and most of what you are producing sits far above the lorry, in a region where there was never any problem. The little that overlaps is doing all the work, so you turn it up, which mostly adds hiss. Play brown noise at the same lorry and the energy is stacked where the lorry is, so a much lower setting covers it. The two colours are not better and worse. One matched and one did not.

There is an asymmetry worth knowing. The masking effect of a sound spreads upward in frequency much more readily than downward. A low-frequency masker covers a considerable range above itself; a high-frequency masker does very little below itself. This is why brown noise is the safer default when you are unsure — it reaches up — and why a bright, hissy noise is close to useless against rumble no matter how loud you make it.

Which Colour for Which Intrusion

Match the sound to the problem. The player at the top of this page carries four colours, so you can settle this in a few minutes against the noise you actually have rather than by reading about it.

Low-frequency intrusions — use brown. Road and rail traffic, aircraft, machinery, a boiler, a washing machine, bass through a floor or ceiling, footfall from above, and a snoring partner. This is the largest category in ordinary homes, because low frequencies are precisely the ones building materials fail to stop.

Speech — use white or green. Conversation through a wall, a television next door, an open-plan office, a housemate on a call. Intelligible speech lives mostly between about 300 Hz and 3.4 kHz, and that band is where white noise has energy and brown noise has comparatively little. Green concentrates the energy in the middle of that range and is often the more comfortable choice for the same effect, because it does not carry white noise's harshness at the top.

Mixed or unknown — start with pink. Pink sits between the two and is the reasonable first attempt when the intrusion is varied or you have not identified it. It is also the most natural-sounding of the four to most people, which matters over eight hours.

Sharp, brief, high sounds — masking will struggle. A dropped plate, a slammed door, a dog. These are dealt with in the limits section below, because the honest answer is that continuous masking handles them poorly and it is better to know that in advance than to conclude the technique failed.

Tinnitus is a different problem and does not belong on this list, because the sound is not arriving from outside and the aim is not the same. It has its own page, with a franker account of the evidence than this category usually offers.

Set the Level Against the Noise, Not Against Silence

The commonest mistake after choosing the wrong colour is choosing the right one and then running it far too loud.

Aim to sit just above the intrusion. The moment the intrusion stops standing out, the masking has done its entire job, and every decibel after that is wasted. If the colour is matched, that point arrives at a surprisingly low setting. If you find yourself pushing the volume up and up, that is not a sign you need more — it is a sign the colour is wrong and you are trying to solve a frequency problem with amplitude.

Set it against the peaks, not the average. Most real intrusions vary. Snoring comes in cycles, traffic comes in vehicles. A level that covers the quiet stretches will let every peak through, and the peaks are what wake you. Listen through a few cycles of whatever you are covering and set the level at the top of them.

Louder is a trade you are making against yourself. Past a point you have not removed an intrusion, you have replaced it with one you chose. You are also spending eight hours a night at a level you selected while awake and irritated, which is not the state in which people judge these things well.

Give it five minutes before deciding. The first thirty seconds of any masking sound feels like an imposition, because you are listening to it. Whether it works is a question about minute four, when you have stopped.

What Masking Cannot Do

It does not reduce your exposure. This is the important one and most pages on this subject leave it out. Masking changes whether you notice a sound. It does not change what reaches you, and adding a masker means the total sound energy in the room goes up rather than down. Night-time noise is associated with measurable effects on sleep that do not require you to wake up and do not require you to remember anything in the morning, which is why the World Health Organization's Environmental Noise Guidelines for the European Region set their strong recommendation for road traffic at below 53 dB L_den and below 45 dB L_night — limits on exposure, not on annoyance. If you are in that situation, masking makes the night more bearable and is worth doing. It is not a substitute for reducing what arrives, and treating it as one is the mistake.

It handles intermittent sound badly. A constant hum is the easy case: the masker only has to sit above a level that never changes. A door slamming at unpredictable intervals is the hard case, because a masker loud enough to cover the peak is far louder than anything the rest of the night requires. Sudden sounds are also the ones the auditory system is most alert to. Continuous masking softens them; it does not remove them.

It does not survive a locked phone. Any browser tab, including the generator on this site, stops when the operating system suspends it, which happens as soon as the screen locks or you switch apps. This is a rule browsers enforce on every website, not a limitation of one page. Overnight masking has to be an installed app or a physical machine.

It is not a treatment for anything. Masking is a way of covering a sound. If sleep has been bad for weeks, or if snoring in the bed comes with gasping or pauses in breathing, the useful next step is a clinician, and no colour of noise changes that.

Masking, Earplugs and Noise Cancelling Do Different Jobs

These three are usually presented as competing answers to one question. They are not. Each works on a different part of the spectrum, and the reason to know that is that it tells you which to reach for, and when to combine two.

Earplugs are worst where household noise is worst. Passive attenuation is strongly frequency-dependent: far more effective at high frequencies than at low. So earplugs deal well with a television and poorly with a lorry or a snore. There is also a hard ceiling — sound reaches the inner ear through bone and tissue regardless of what is in the ear canal, and measurements of that limit put it in the region of 40 to 60 dB across the audible range (Berger, Kieper & Gauger, 2003). Beyond it, better earplugs stop helping. The full comparison is here.

Active noise cancellation is the exact opposite. It works best at low frequencies and tails off higher up, which is why it is transformative on an aircraft and unimpressive against a conversation. That makes it a genuine complement to earplugs rather than an alternative — but it needs headphones, and headphones are not something most people can sleep in comfortably all night.

Masking is the one that scales to a whole room and a whole night. It costs nothing, needs nothing in or on your ears, works for two people in a bed rather than one, and is the only one of the three that can be matched to the specific frequency region causing the problem.

The best answer is often two of them. Earplugs plus brown noise is a strong combination precisely because their weaknesses do not overlap: the plugs take out the high end, brown noise covers the low end that gets past them. This site sells neither, so there is no reason to pretend one wins.

If You Only Read One Paragraph

Masking does not reduce the sound reaching you; it raises the background so the sound no longer stands out, and hearing responds to that contrast rather than to absolute level. Because the comparison happens inside narrow frequency bands, only the part of your masking sound that overlaps the intrusion does any work — so match the colour first and set the volume second. Brown for traffic, machinery, bass and snoring; white or green for speech; pink when you are not sure. Set the level just above the peaks of what you are covering and no higher. Masking will not lower your exposure, will not handle sudden sounds well, and is not a treatment for anything.

Frequently Asked Questions

Related pages

• Block Out Snoring — Snoring is the hardest sound to mask: low, uneven, and a metre from your head with no wall in the way. What actually helps.
• Block Traffic Noise — Your walls already stripped the top off the traffic outside. That is why brown noise covers it indoors and white noise does not.
• Masking vs Earplugs — Earplugs work least well exactly where household noise is worst. Masking can be aimed. Why the answer is usually both.
• Brown Noise Machine — Two very different products are sold as a brown noise machine, and one of them cannot make brown noise. What to check before buying.
• Brown Noise — The deepest colour, measured at −5.98 dB per octave — best for traffic rumble and long overnight sessions.
• White Noise — The flat reference colour, measured at 0.00 dB per octave — the best of the five at making speech unintelligible.
• Green Noise — The mid-frequency colour — a pink base with a broad 500 Hz emphasis, and the only one of the five with no standard definition.
• Pink Noise — Equal energy in every octave, measured at −3.07 dB per octave — the natural-sounding default and the audio industry's calibration signal.
• Brown vs White Noise — The widest gap on the site — 5.98 dB per octave, about 38 dB apart by 8 kHz — and what each colour can and cannot cover as a result.
• Brown Noise Generator — A real brown noise generator in the browser: built live at a measured -5.98 dB per octave, with no file and no loop point.
• About — Who publishes this site, how the brown noise is generated in-browser, and how we handle health topics.
• Block Neighbour Noise — Bass and footfall need brown noise. Voices through a wall need white or green. Most advice gives one answer to both.