The Colors of Noise: Therapeutic to Engineering Uses

Ian C. Langtree - Writer/Editor for Disabled World (DW)
Published: 2025/02/09 - Updated: 2025/02/10
Publication Type: Informative
Topic: Medical Calculators and Charts - Publications List

Page Content: Synopsis - Introduction - Main

Synopsis: White, pink, brown, blue, and other noise variants serve distinct applications based on their spectral properties, ranging from audio engineering to therapeutic uses.

Why it matters: This article provides an authoritative overview of noise types categorized by their frequency distributions, explaining their technical properties, real-world applications, and benefits for diverse audiences. It details how white, pink, brown, blue, and lesser-known noise variants like gray or violet serve distinct purposes - from masking distractions and enhancing sleep to aiding audio engineering and medical research. The piece highlights practical uses for individuals with specific needs, such as brown noise for ADHD focus, pink noise for Neurodivergent sound sensitivity, and gray noise tailored for hearing-impaired users. It also explores applications for seniors, including low-frequency noise to mask tinnitus or urban disturbances, and therapeutic soundscapes mimicking natural environments for relaxation. By bridging technical concepts with accessible examples - like thunderstorms, ocean waves, or customized audio tools - the article acts as a valuable resource for anyone seeking to improve sleep, concentration, or auditory health, while offering insights for professionals in acoustics, healthcare, and technology - Disabled World (DW).

Introduction

Noise types are categorized by how their energy distributes across frequencies: White noise contains all frequencies at equal intensity, like TV static, and is used for masking distractions or testing audio gear. Pink noise emphasizes deeper tones (think steady rain), balancing natural sounds for relaxation or tuning concert halls. Brown noise rumbles with even heavier bass - similar to a thunderstorm - and helps mask low-frequency disturbances or aids focus. Blue noise tilts toward sharp highs, such as a hissing hose, and is key for technical tasks like audio dithering or printing halftones. Other variants like violet (ultra-high frequencies) or gray (tailored to human hearing) serve niche roles in research, therapy, or sound engineering, proving these aren't just abstract concepts but tools shaping everything from sleep apps to high-tech imaging.

Main Item

Noise Types Explained in Detail

Listed below is a detailed breakdown of each noise type, including their technical properties, common uses, and real-world examples, followed by additional noise types.

Jump to:

White Noise

Technical Definition:

• Equal power per frequency (flat power spectral density).
• Energy is distributed uniformly across all audible frequencies (20 Hz–20 kHz).
• Power Slope: 0 dB/octave (no roll-off).

Characteristics:

• Sounds like a steady "hiss" (e.g., untuned radio static).
• Contains all frequencies at equal intensity, which can be harsh to human ears over time.

Uses:

• Sleep and Focus: Masks sudden noises (e.g., barking dogs, traffic) by filling the auditory spectrum.
• Audio Engineering: Calibrating microphones, testing speaker frequency response.
• Tinnitus Relief: Helps distract from ear ringing.
• Privacy: Used in offices or hospitals to obscure conversations.

Examples:

• Hair Dryer: The sound of a hair dryer when it's running.
• Wind: The sound of wind blowing through trees or against windows.
• Hissing of Steam: From radiators or steam escaping in industrial settings.
• Rain on a Window or Roof: The patter of rain can create a white noise effect.
• Vacuum Cleaner: The consistent drone of a vacuum cleaner can be quite effective.
• Hum of a Refrigerator: The constant background noise from a refrigerator's motor.
• Air Conditioner Hum: The constant, low-level hum produced by an air conditioning unit.
• Fan Noise: The sound of an electric fan, either a desktop model or a ceiling fan, running at a steady speed.
• Static on a Radio or TV: The static sound you hear when a radio or television isn't tuned to a station or channel.
• Shower or Running Water: The sound of water running in a shower, sink, or even a waterfall can act as white noise.
• White Noise Machines: Devices specifically designed to produce white noise, often with adjustable tones and volumes.
• Electronic Noise from Speakers: When audio equipment is on but no source is playing, it might emit a low-level hiss.
• Ocean Waves: Although not technically white noise, the continuous crashing of waves can have a similar soothing effect.
• White Noise Apps: Many apps provide digital versions of white noise, including variations like pink noise or brown noise.

Each of these white noises can help mask other sounds, aid in concentration, or assist with sleep by providing a consistent sound backdrop. Remember, while these are generally referred to as white noise, some might technically be pink, brown, or another color of noise, which differ slightly in their frequency distribution but serve a similar purpose in many contexts. See below for further information and examples.

Pink Noise

Technical Definition:

• Equal powerper octave(energy decreases by 3 dB per octave as frequency increases).
• Emphasizes lower frequencies more than white noise.

Characteristics:

• Sounds "warmer" and more balanced (e.g., steady rainfall).
• Matches human hearing sensitivity, which perceives lower frequencies as louder.

Uses:

• Acoustic Testing: Tuning concert halls, studios, or speaker systems for balanced sound.
• Sleep Enhancement: Studies suggest it may improve sleep quality and memory retention during deep sleep.
• Sound Therapy: Reduces auditory hypersensitivity in neurodivergent individuals.
• Machine Burn-in: Used to test audio equipment durability.

Examples:

Here are some examples of sounds that are often described as pure or predominantly pink noise, without significant overlap from other color noises:

• Gentle Surf: The sound of small waves lapping at the shore, more subdued than large crashing waves.
• Wind Through Trees: The rustling sound of wind through foliage, when it's a low, steady whoosh, can be pink noise.
• Slow Drumming: A slow, steady beat on a large drum can produce a sound akin to pink noise, focusing on lower frequencies.
• Steady Rain: The sound of rain falling consistently on a hard surface, like a roof or pavement, can closely mimic pink noise.
• Heartbeat: The steady, rhythmic sound of a heartbeat, especially when amplified through a stethoscope, can be akin to pink noise.
• Waterfall: The continuous roar of a waterfall, especially when it's a single, uninterrupted flow, can be very close to pink noise characteristics.
• Ocean Waves: Specifically, the sound of waves crashing and then retreating on a beach, when captured from a distance, can be considered pink noise.
• Blowing Across a Bottle: If you blow across the top of a bottle to make a deep, resonant sound, this can mimic pink noise qualities at lower volumes.
• Electrical Hum: The hum from some electrical devices, particularly older transformers, can sometimes be considered pink noise if it's a broad, low-frequency sound.
• Pink Noise Generators: Devices or apps specifically designed to produce pink noise, which by definition, have equal energy per octave, leading to a sound that decreases in intensity as frequency increases.

In real-world settings, achieving absolutely no overlap with other color noises can be challenging, as most natural sounds are a mix. These examples, however, are generally recognized for their pink noise characteristics when experienced in isolation or in settings where the sound is dominant.

Brown Noise (Red Noise)

Technical Definition:

• Power decreases by 6 dB per octave (steeper roll-off than pink noise).
• Named after Brownian motion (random particle movement), not the color.

Characteristics:

• Deep, rumbling bass with minimal high frequencies.
• Often described as "soothing" or "earthy."

Uses:

• ADHD Focus: Helps some individuals concentrate by masking distractions.
• Tinnitus and Hyperacusis: Masks low-frequency ringing or sensitivity.
• Meditation/Relaxation: Mimics calming natural sounds.
• Sound Isolation: Blocks low-frequency noises like HVAC systems.

Examples:

• Rumbling Thunder: The distant or low rumbling of thunder provides that deep, bass-heavy sound characteristic of brown noise.
• Waterfalls: The roar of a waterfall, especially close up, where the sound is dominated by the low-frequency rumble of the water.
• Heavy Rainfall: The steady sound of heavy rain hitting a roof or ground can mimic the deep, low-frequency quality of brown noise.
• Traffic from a Distance: The distant hum of traffic, especially on highways or in tunnels, can blend into a deep, rumbling brown noise.
• Heartbeat: The sound of a heartbeat, amplified or through a stethoscope, has a low, rhythmic quality that can be likened to brown noise.
• Rushing Rivers or Streams: Fast-flowing water over rocks, especially in a gorge or through a canyon, produces a bass-heavy, rumbling sound.
• Wind in Trees or through Buildings: Strong winds blowing through dense forests or around high-rise buildings can create a low, rumbling sound.
• Airplane or Jet Engine Noise: The sound of a jet engine, particularly from inside the aircraft, has a deep, continuous drone that can be similar to brown noise.
• Heavy Machinery: Sounds from large industrial machines like compressors, large fans, or even a running washing machine can produce noise similar to brown noise.
• Ocean Waves: The sound of large waves crashing against the shore or cliffs, especially during a storm, can be very close to brown noise with its deep, resonant tones.

These brown noise examples are often used in noise apps or sound machines specifically for their calming, focus-enhancing, or sleep-inducing properties. If you're interested in experiencing or using brown noise, you might want to look into noise generators or playlists available on platforms like Spotify or YouTube, where you can find dedicated tracks for brown noise.

Blue Noise

Technical Definition:

• Power increases by 3 dB per octave (opposite of pink noise).
• High-frequency emphasis with minimal low frequencies.

Characteristics:

• Sharp, "crisp" hiss (e.g., steam release or water spray).
• Rarely used for relaxation due to its piercing quality.

Uses:

• Audio Dithering: Reduces quantization errors in digital audio by masking artifacts.
• Image Halftoning: Creates patterns for printing (e.g., newspaper images).
• High-Frequency Testing: Evaluates tweeters or ultrasonic equipment.

Examples:

• Breaking Glass: Not the entire sound but the initial high-frequency crack or shatter can have characteristics of blue noise before the lower frequencies take over.
• Steam Escaping: The noise of steam escaping from a kettle or a steam pipe often has a blue noise component because of the high-pitched, continuous nature of the sound.
• Ultrasonic Cleaners: These devices use high-frequency sound waves in water to clean objects, and the sound they produce, when audible, can mimic the properties of blue noise.
• Electronic Fan Noise: Some fans, especially those with small blades or high speeds, can produce a sound that approaches blue noise, especially if they're running at high RPMs.
• Insect Buzzing: The collective sound of many small insects like mosquitoes or flies can sometimes resemble blue noise due to the high-pitched, non-rhythmic nature of their buzzing.
• Sandpaper on Wood: The sound of sanding wood with high-grit sandpaper can produce a very high-frequency, blue noise-like sound due to the friction and small particles being removed.
• High-Frequency Static: The kind you might hear from an old TV set or radio when it's not tuned to a station. Blue noise has more energy at higher frequencies, which makes it sound very "hissy" or "fizzy."
• Wind Through a Small Gap: When wind rushes through a narrow opening, like between buildings or through a slightly open window, it can produce a high-frequency whistling or hissing sound akin to blue noise.
• Breath Sounds: If you listen closely to someone breathing through their nose rapidly or during heavy exercise, the breath can sometimes take on qualities of blue noise, especially if there's some nasal congestion.
• Water Spraying: Think of the sound of a fine mist spray bottle or a showerhead with many small holes creating a high-pitched, continuous spray. This sound has characteristics of blue noise due to its high-frequency components.

Blue noise is characterized by its power distribution, where power density increases with frequency. This means it sounds "brighter" and more "hissy" than white noise, which has equal intensity at all frequencies. Each of these examples might not be pure blue noise but shares some of its auditory characteristics.

Additional Noise Types

There are also many colors used without precise definitions (or as synonyms for formally defined colors), sometimes with multiple definitions.

Violet Noise (Purple Noise)

Technical Definition:

• Power increases by 6 dB per octave (steeper high-frequency emphasis than blue noise).

Uses:

• Testing high-frequency audio equipment (e.g., ultrasound devices).
• Studying high-frequency hearing loss or tinnitus.

Examples:

Violet noise, also known as purple noise, is characterized by a power density that increases with frequency, making it sound very high-pitched. Here are some examples of violet noise or situations where you might encounter similar sound characteristics:

• A sprinkler or hose leaking steam: Similar to the water faucet, the high-pitched hiss of steam escaping can resemble violet noise.
• The sound of a fully open water faucet: This mimics the high-frequency sound profile of violet noise, where you hear the sharp, hissing sound of water.
• Tinnitus relief sounds: Some sound therapies for tinnitus use violet noise because its high frequencies can help mask the ringing sounds in the ears for some individuals.
• Audio applications for testing: Violet noise can be used in audio engineering for testing speakers or systems at high frequencies to check for distortions or other issues.
• High-frequency electrical noise: Sometimes in electronic devices, especially when there's interference or signal noise, you can hear a sharp, high-frequency sound akin to violet noise.
• Hydrophone background noise: When listening to underwater sounds, the background noise captured by hydrophones can sometimes resemble violet noise due to the concentration of energy in higher frequencies.
• Dithering in digital audio: In audio engineering, violet noise can be used as dither, which is a technique to reduce quantization error in digital audio by adding noise to the signal, particularly focusing on high frequencies.

While these examples don't perfectly replicate violet noise, they share similar sound characteristics or are used in contexts where violet noise might be applicable or effective. Remember, the actual experience of these sounds can be quite subjective, and how one perceives violet noise might differ from person to person.

Gray Noise

Technical Definition:

• Adjusted for equalperceived loudnessacross frequencies (compensates for human hearing curves).

Uses:

• Hearing tests and auditory research.
• Sound masking tailored to individual hearing profiles.

Examples:

• Fans: The sound of an electric fan running, particularly at a steady, medium speed.
• Air Conditioners: The background hum of an air conditioning unit, especially when it's not cycling on and off.
• Washing Machines: The noise during the washing or spin cycle, where the sound is consistent and somewhat balanced across frequencies.
• Rain on a Window: The sound of steady, light rain hitting a window or roof can mimic gray noise, offering a balanced spectrum of sound.
• HVAC Systems: The background noise from heating, ventilation, and air conditioning systems in buildings, which often have a balanced spectrum.
• Vehicle Travel: The drone of tires on a highway or the engine noise of a car at a steady speed can sometimes produce sounds close to gray noise.
• White Noise Machines: Some modern white noise machines have settings for gray noise, which adjusts the power spectrum to make mid-range frequencies more prominent.
• Sound of the Sea: Waves crashing on the shore at a consistent pace can sometimes be categorized as gray noise due to the even distribution of sound across different frequencies.
• Vacuum Cleaners: The consistent noise from a vacuum cleaner, which, although typically considered white noise, can have a gray noise component due to its balance across frequencies.
• Shower Sounds: The continuous sound of water from a shower can often be described as gray noise, especially when the water hits various surfaces creating a balanced sound frequency.

Gray noise aims to have equal energy per octave, making it sound less harsh than white noise to the human ear since it puts more emphasis on the frequencies we're more sensitive to. The perception of gray noise can be somewhat subjective, as what one person might consider gray noise, another might categorize differently based on their auditory experience.

Green Noise

Technical Definition:

• Focused on mid-frequencies (~500 Hz), resembling natural environments.

Uses:

• Stress relief and nature soundscapes.
• Masking urban noise (e.g., traffic hum).

Examples:

Here are some examples of green noise, which is known for its calming and soothing qualities due to its frequency distribution:

• Light Rain: The patter of soft rain on leaves or windows can mimic green noise, promoting relaxation or sleep.
• Air Conditioner: Similar to a fan, an air conditioner can produce a soothing, continuous hum that can be akin to green noise.
• Ocean Waves: While the ocean can produce various types of noise, a consistent, gentle wave sound can be categorized as green noise.
• Water Streams: The sound of a gentle stream or small waterfall often has characteristics of green noise, providing a calming backdrop.
• Shower Running: The sound of water from a shower can resemble green noise, particularly if it's a consistent flow without too much variation.
• Wind Through Trees: The rustling of leaves or the sound of wind through pine trees can create a green noise effect, especially when it's not too gusty.
• Fan Noise: A fan set to a lower speed can sometimes produce sounds close to green noise, especially if it has a gentle hum without high-pitched whines.
• Nature Soundscapes: Recordings or apps that feature sounds of the forest or nature walks might include elements of green noise, enhancing the natural ambiance.
• White Noise Machines with Green Noise Settings: Many modern sound machines offer green noise options specifically tuned to the frequencies that are most soothing.
• Soft, Continuous Traffic: From a distance, the sound of traffic can sometimes blend into a green noise-like background if it's consistent and not too loud or disruptive.

Green noise focuses on the mid-frequencies, making it less harsh than white noise and more soothing than pink noise. If you're interested in experiencing green noise for relaxation or sleep, you might want to explore apps or devices that offer these sounds or look for natural environments that provide similar auditory experiences.

Black Noise

Technical Definition:

• Either (1) near-silence
• or (2) ultra-low frequencies (<20 Hz).

Uses:

• Theoretical applications in sub-bass music production.
• Represents "silence" in noise-cancellation contexts.

Examples:

• Infrasound: Sounds at frequencies below 20 Hz, which can be considered black noise because they are generally inaudible to humans but can be felt or detected by sensitive equipment.
• Technical Silence: Black noise is often described as the absence of sound or silence, but with the possibility of very low-frequency vibrations that are below the human hearing threshold.
• Silence in Noise: Some definitions extend black noise to a state where there's almost no sound, but with occasional, very brief moments of sound, creating a paradoxical sense of silence that isn't completely silent.
• Black Noise in Art and Literature: Conceptually, black noise has been used to describe a form of silence with profound implications in art, like the "Black Noise" art project which explores the relationship between sound and silence.
• Incomplete Silence with Random Spikes: An example given in noise theory is from a facsimile transmission system where scanning a black area might show a spectrum with almost zero power level across frequencies except for a few random white spots, leading to occasional pulses in time domain.
• Weaponized Infrasound: The idea of "black noise" as a potential weapon was discussed by David Bowie and William S. Burroughs, where infrasound could be used at a frequency to cause physical effects, like cracking glass or disorienting people, hence termed as a "noise bomb" or "black noise bomb."

These examples highlight black noise not just as a type of noise but as a concept in physics, art, and even speculative technology, where the absence of sound or presence of inaudible vibrations plays a key role. Whale noises are not considered "black sound" or "black noise."

Orange Noise

Technical Definition:

• Semi-periodic, dissonant sound (e.g., clashing musical intervals).

Uses:

• Experimental music/sound design.
• Studying auditory perception of dissonance.

Examples:

Here are some examples of what might be considered orange noise, given its unique, dissonant quality:

• Scrambled Voice Audio: An audio recording where the pitch and speed are altered randomly, not to produce a coherent musical effect but to create an unsettling, off-key noise.
• Choir Singers Out of Sync: Imagine a choir where each singer is slightly off-key or singing at different speeds or in different keys intentionally, leading to a discordant blend of voices.
• Malfunctioning Synthesizer: A synthesizer that's not properly calibrated, producing notes that are off-pitch or fluctuating in an erratic manner, could produce a sound similar to orange noise.
• Random Frequency Generator: A device or software that randomly generates frequencies without regard to musical scales, particularly if it avoids or includes only non-musical pitches, could simulate orange noise.
• Distorted Radio Signal: A radio signal that's picked up with heavy static or interference, where the intended broadcast frequencies clash with unintended signals, creating a cacophony rather than clear music or speech.
• Broken or Misused Musical Instrument: Playing an instrument in a way that produces sounds not intended for music, like tapping on the body of a guitar or playing several keys on a piano at once in a non-harmonious way.
• Sound Art Installations: Artists might use orange noise in sound installations where the goal is to explore or challenge the auditory experience, perhaps using feedback loops or unusual sound sources to create this effect.
• Clashing Wind Chimes: Wind chimes tuned to non-musical intervals or where each chime is deliberately off-pitch from standard musical notes, resulting in a jangling, unharmonious sound.
• Nature's Discord: In nature, orange noise might be akin to the cacophony of different bird species calling out simultaneously but in disharmony, or the sound of wind through broken or oddly shaped structures, creating a dissonant wind sound.

These examples illustrate how orange noise might be conceptualized or created, focusing on the aspect of dissonance and the absence of musical coherence. The exact sound of "orange noise" isn't universally standardized, so these examples offer a creative interpretation based on the general understanding of noise colors.

Thermal Noise (Johnson-Nyquist Noise)

Technical Definition:

• White noise generated by electron movement in conductors (physics/engineering term).

Uses:

Here is a list of examples where you might observe or deal with Thermal Noise, often referred to as Johnson-Nyquist Noise:

• Astronomy Detectors: In ground-based or space telescopes, the inherent thermal noise of the detector systems can be a limiting factor in detecting faint celestial objects or signals.
• Microphones: In high-quality audio systems, even the microphone's internal electronics can introduce thermal noise, especially in quiet environments where the noise becomes more noticeable.
• Photodetectors: In optical communication systems or photodiodes used in scientific instruments, thermal noise from the resistance of the photodetector can limit the sensitivity of the device.
• Quantum Computing: Even in highly controlled environments, thermal noise can affect the coherence time of qubits, as they are extremely sensitive to any form of noise, including thermal fluctuations.
• Medical Diagnostic Equipment: In devices like electrocardiograms (ECGs) or electroencephalograms (EEGs), thermal noise can be a factor in the baseline noise level, potentially masking small signal changes.
• Capacitors at High Frequencies: Though capacitors are often thought of as noise-free, at high frequencies, their equivalent series resistance (ESR) can generate thermal noise, affecting high-frequency circuits.
• Antennas: When receiving weak signals, especially in radio astronomy or satellite communications, the antenna itself can contribute thermal noise due to the resistance of its components, affecting the signal-to-noise ratio.
• Thermal Imaging Cameras: While not noise in the traditional sense, the detectors in thermal imaging cameras have to deal with thermal noise from their own components, which can limit the resolution or sensitivity of the image.
• Semiconductor Devices: Transistors and diodes at room temperature will exhibit thermal noise, which can be particularly problematic in low-noise amplifiers used in physics experiments or in the front end of communication receivers.
• Resistors in Electronic Circuits: Any resistor at a non-zero temperature will generate thermal noise. This noise is proportional to the temperature and the resistance value. For instance, in audio amplifiers or radio frequency (RF) circuits, this noise can degrade the signal quality.

Thermal noise is fundamentally random and follows a white noise spectrum, meaning it's evenly spread across all frequencies. Its power spectral density is given by Nyquist's formula, which states that it's proportional to temperature and resistance but inversely proportional to bandwidth.

Practical Applications Summary

• Creative: Green/orange noise in music production and soundscapes.
• Therapeutic: White, pink, and brown noise aid sleep, focus, and relaxation.
• Technical: Blue/violet noise for audio/image processing; gray noise for audiology.

Each noise type serves unique roles based on its spectral profile, from masking distractions to enabling cutting-edge technology.

Author Credentials: Ian was born and grew up in Australia. Since then, he has traveled and lived in numerous locations and currently resides in Montreal, Canada. Ian is the founder, a writer, and editor in chief for Disabled World. Ian believes in the Social Model of Disability, a belief developed by disabled people in the 1970s. The social model changes the focus away from people's impairments and towards removing barriers that disabled people face daily. To learn more about Ian's background, expertise, and achievements, check out his bio.