Understanding Colored Noise: Exploring the Sound Spectrum
When we think of noise, we usually think of the sounds noises make - honking, shrieking, purring, melodious, rhythmic, etc. You probably rarely find yourself talking about the colors of noise. Colored noise is a term that references a category of sleep sounds, but it also has other applications that might enhance your life in other ways. As we will explore in this article, each color of noise has different properties, applications, and benefits beyond just better sleep.
The idea of the colors of noise uses the idea of color to describe certain frequencies of noise, starting with white noise, which most people understand is a blanket of sound that drowns out other sound, in the same way white light combines and therefore drowns out all other colors of light.
In audio engineering, electronics, physics, and many other fields, the color of noise or noise spectrum refers to the power spectrum of a noise signal (a signal produced by a stochastic process). Different colors of noise have significantly different properties. For example, as audio signals they will sound different to human ears, and as images they will have a visibly different texture. Therefore, each application typically requires noise of a specific color.
The practice of naming kinds of noise after colors started with white noise, a signal whose spectrum has equal power within any equal interval of frequencies. That name was given by analogy with white light, which was (incorrectly) assumed to have such a flat power spectrum over the visible range. Other color names, such as pink, red, and blue were then given to noise with other spectral profiles, often (but not always) in reference to the color of light with similar spectra. Some of those names have standard definitions in certain disciplines, while others are informal and poorly defined.
Many of these definitions assume a signal with components at all frequencies, with a power spectral density per unit of bandwidth proportional to 1/f β and hence they are examples of power-law noise. For instance, the spectral density of white noise is flat (β = 0), while flicker or pink noise has β = 1, and Brownian noise has β = 2.
Various noise models are employed in analysis, many of which fall under the above categories. AR noise or "autoregressive noise" is such a model, and generates simple examples of the above noise types, and more.
The color names for these different types of sounds are derived from a loose analogy between the spectrum of frequencies of sound wave present in the sound (as shown in the blue diagrams) and the equivalent spectrum of light wave frequencies.
Colored Noise Versus Music
Colored noise is different from music in that it doesn’t have a rhythm, beat, or any discernible patterns or melodies. Each type of colored sound is random noise that falls within a certain band of the spectrum of audible sound, giving your ear a different impression or feeling when you hear it. Additionally, which variety of colored noise someone enjoys or benefits from varies from person to person. Just like music, we all have our own favorite color of noise.
Why Are Noise Types Named After Colors?
Color-based names for noise help to distinguish and remember what sets them apart from each other. To understand why certain types of random noise got their names from colors, let's briefly visit the audible sound spectrum using the analogy of the visible light spectrum. Think about a rainbow, where different colors represent different frequencies of light. Colored noise is like this, but with sound frequencies.
In the same way that white light is a mixture of all the colors in the rainbow, white noise has equal energy across all audible frequencies of the sound spectrum. Each color of noise represents a different combination of frequencies and volumes along the spectrum of sound. So, when we say "colored noise," we are essentially describing a sound that has a specific frequency pattern, and naming it after colors helps us visualize and remember these patterns more easily.
The human ear can hear frequencies ranging from 20Hz to 20,000Hz. These frequencies are divided into different ranges or bands, like bass (lower frequencies), midrange, and treble (higher frequencies), where each band has a different color.
If you are interested in understanding the technical differences in composition of all the colors of noise, you can find a great explanation on the Sound Speeds YouTube Channel.
Applications for Colored Noise - Why Use Colored Noise?
One of the most common applications of colored noise is to improve sleep by making it easier to fall asleep or by keeping you asleep longer. Colored noise does this in two ways. First, by masking environmental sounds. Second, by influencing your brain and body toward states conducive to relaxation and deep sleep.You can also use colored noise to help you focus and concentrate, or to relax.
You might try colored noise to improve the conditions for journaling, reading, yoga, or meditation. It can also help you read, write, or study and retain information. While it’s not a replacement for medical interventions, some people find that colored noise can provide some relief for a variety of health challenges, such as tinnitus, sleep disorders, mental health conditions, stress and anxiety management, sensory processing disorders, and some cognitive conditions.
You can try colored noise to:
- Improve focus
- Boost productivity
- Enhance creativity and memory
- Decrease fatigue or brain fog
- Increase mental clarity or sharpness
- Relax the mind and body
- Enhance your sense of presence for yoga or meditation
- Soothe stress and anxiety
- Help put your baby or toddler to sleep
- Reduce irritation or distraction caused by other sounds in your environment
The 7 Colors of Noise Explained
Below is an overview of the different types of colored noise, from the familiar white noise to the more obscure violet noise.
Simulated power spectral densities as a function of frequency for various colors of noise (violet, blue, white, pink, Brown/red). The power spectral densities are arbitrarily normalized such that the value of the spectra are approximately equivalent near 1 kHz.
White Noise: The Standard Sleep Sound
Distinguishing feature: Equal energy across all audible frequencies.
People have been using white noise for better sleep since before sleep noise became popular! Think of the rushing or hissing sounds of tv or radio static and the steady hum from a fan, a vacuum, or an air conditioning unit. This color of noise is characterized by its even or flat sound-it contains all frequencies in the audible spectrum at equal amplitude. So, high frequencies are heard as equally loud and balanced with midrange and low frequencies, all at the same time. White noise provides the most consistent background noise, best for masking other environmental sounds.
White noise is great for light sleepers to fall asleep and stay asleep. If you find that you wake up easily, you can try white noise to help you stay asleep no matter what is happening in the room around you. The same goes for putting babies and toddlers to bed! White noise can also help you write and read faster, retain more information, focus better, and help you manage the symptoms of ADHD.
Examples: fan, vacuum, air conditioner, tv or radio static
Pink Noise: Study and Sleep Support
Distinguishing feature: More amplitude in the lower frequencies and decreasing amplitude with higher frequencies. Louder low frequencies and slightly softer mid and high frequencies.
If you want a softer background noise or if you find high-frequency sounds too sharp, you might find pink noise better for relaxation and sleep. Where white noise is great for getting to sleep, pink noise can help you stay asleep longer. Sleeping to pink noise might also boost your memory after you wake up. You might try pink noise to enhance productivity if you are trying to study in a cafe or work in a busy office with lots of environmental noise.
The frequency spectrum of pink noise is linear in logarithmic scale; it has equal power in bands that are proportionally wide. This means that pink noise would have equal power in the frequency range from 40 to 60 Hz as in the band from 4000 to 6000 Hz. Since humans hear in such a proportional space, where a doubling of frequency (an octave) is perceived the same regardless of actual frequency (40-60 Hz is heard as the same interval and distance as 4000-6000 Hz), every octave contains the same amount of energy and thus pink noise is often used as a reference signal in audio engineering. The spectral power density, compared with white noise, decreases by 3.01 dB per octave (10 dB per decade); density proportional to 1/f.
Examples: rustling leaves, the hum inside an airplane cabin, the hum of a fridge, steady rain on a tin roof.
Brown Noise: Deep and Soothing
Distinguishing feature: Low frequencies are emphasized and high frequencies are barely audible-a more pronounced decrease in energy with increasing frequency compared to pink noise.
Brown noise is deeper than pink or white noise because it emphasizes the bass frequencies of sound, which you might find particularly soothing, and all the other frequencies are softer and less audible. Sometimes called Brownian noise or red noise, brown noise is best for a deep and uninterrupted sleep. Like pink and white noise, it can also enhance relaxation and focus or lengthen your attention span. Try brown noise for better reading comprehension!
Brownian noise, also called Brown noise, is noise with a power density which decreases 6.02 dB per octave (20 dB per decade) with increasing frequency (frequency density proportional to 1/f2) over a frequency range excluding zero (DC). Brownian noise can be generated with temporal integration of white noise. "Brown" noise is not named for a power spectrum that suggests the color brown; rather, the name derives from Brownian motion, also known as "random walk" or "drunkard's walk".
Examples: rumbling thunder, strong winds, a purring cat, crackling fire.
Green Noise: A Naturally Calming Noise
Distinguishing feature: Emphasizes the middle of the sound spectrum, so mid-range frequencies are heard the most while the extreme lows and highs aren’t as audible.
Green noise provides you with a reliable, calming background noise buffer. It falls into the mid-range of the sound frequency spectrum, so you won’t be bothered by any extreme treble or bass. It drowns out other distracting sounds while also soothing symptoms of anxiety and ADHD. Try green noise if you want to feel relaxed and focused at the same time. Whether you are trying to work, read, write, or sleep, green noise can help!
That is, it is similar to pink noise, but with different spectral content and different relationships. Joseph S. Wisniewski writes that "green noise" is marketed by producers of ambient sound effects recordings as "the background noise of the world". It simulates the spectra of natural settings, without human-made noises.
Examples: heavy rainfall, rolling waves, soft breezes through a forest, driving noise.
Blue Noise: A Lively Concentration Sound
Distinguishing feature: The reverse of brown noise, the high frequencies are more pronounced than the low frequencies-mostly treble with hardly any bass.
Blue noise has a bright and lively quality. While low-frequency sounds are present, they are less audible while the high-frequency sounds are emphasized. You might still use it for sleep, but it is more likely useful for situations where you need to get things done! It encourages a sense of alertness, mental clarity, concentration, and focus.
Blue noise is also called azure noise. Blue noise's power density increases 3.01 dB per octave with increasing frequency (density proportional to f ) over a finite frequency range. In computer graphics, the term "blue noise" is sometimes used more loosely as any noise with minimal low frequency components and no concentrated spikes in energy. Cherenkov radiation is a naturally occurring example of almost perfect blue noise, with the power density growing linearly with frequency over spectrum regions where the permeability of index of refraction of the medium are approximately constant. The exact density spectrum is given by the Frank-Tamm formula. In this case, the finiteness of the frequency range comes from the finiteness of the range over which a material can have a refractive index greater than unity.
Examples: a hissing hose, steam leaking from a pipe, or computer fan noise.
Violet Noise: The Most Uplifting Focus Noise
Distinguishing feature: the high frequencies are even more pronounced than in blue noise-all treble and no bass.
Violet, or purple, noise is a more extreme version of inverted brown noise. It is the most crisp and bright-sounding of all the colored noise types. You might use it to stay awake on a long night drive or to improve focus, attention, and memory while reading, working, or studying. Violet noise is best for masking high-frequency sounds in your environment, especially if you have tinnitus. It sounds like a high-pitched hiss or sizzle, a lot like running water from a faucet.
Violet noise is also called purple noise. Violet noise's power density increases 6.02 dB per octave with increasing frequency "The spectral analysis shows that GPS acceleration errors seem to be violet noise processes. They are dominated by high-frequency noise." (density proportional to f 2) over a finite frequency range.
Examples: running water from a faucet.
Gray Noise: The Smoother White Noise
Gray noise is like a smoothed-out version of white noise or pink noise that is perceptually more balanced to the human ear. It is the most even-sounding of the colored noises with any variations in volume from frequency to frequency melting into each other.
Black Noise: The Absence of Sound
Just like the color black is the absence of light, black noise is the absence of sound, with zero power at all frequencies.
Noise with a spectrum corresponding to the blackbody radiation (thermal noise). For temperatures higher than about 3×10−7 K the peak of the blackbody spectrum is above the upper limit of human hearing range. In those situations, for the purposes of what is heard, black noise is well approximated as violet noise. At the same time, Hawking radiation of black holes may have a peak in hearing range, so the radiation of a typical stellar black hole with a mass equal to 6 solar masses will have a maximum at a frequency of 604.5 Hz - this noise is similar to green noise.
Note: An example of black noise in a facsimile transmission system is the spectrum that might be obtained when scanning a black area in which there are a few random white spots.
A formula is: Hz.
The conceptual diagram of the generation of the color noise.
Choosing the Right Noise for Your Needs
The type of noise that works best for you will depend a lot on personal preference, as well as what you’re hoping to achieve. For example, you may find that blue noise helps you get work done, but isn’t all that helpful for sleeping. Another person might find the opposite is true. That’s why choosing the right noise color for you will require a bit of experimentation.
If you are looking for help with sleep or relaxation, you might start with white, pink, or brown noise. If you want to get your brain focused and working, green, blue, or violet noise might be your first choice. As you explore the differences between the different colored noise types, you might find some annoying or soothing, and what works well for one person may not work the same for the next person. The best approach to finding your ideal noise color is to use the overview provided in this article and try different ones to find out which has the effect you’d like.
| Noise Color | Distinguishing Feature | Best For | Examples |
|---|---|---|---|
| White Noise | Equal energy across all audible frequencies | Masking environmental sounds, light sleepers | Fan, vacuum, air conditioner, TV static |
| Pink Noise | More amplitude in lower frequencies | Relaxation, sleep support, memory boost | Rustling leaves, airplane cabin hum, steady rain |
| Brown Noise | Emphasized bass frequencies | Deep sleep, uninterrupted sleep | Rumbling thunder, strong winds, purring cat |
| Green Noise | Emphasizes the middle of the sound spectrum | Calming anxiety and ADHD | Heavy rainfall, rolling waves, soft breezes |
| Blue Noise | High frequencies more pronounced | Alertness, mental clarity, concentration | Hissing hose, steam leaking from a pipe |
| Violet Noise | High frequencies even more pronounced | Staying awake, improving focus | Running water from a faucet |
| Gray Noise | Smoothed-out version of white noise | Balanced sound | - |
| Black Noise | Absence of sound | Zero power at all frequencies | - |