Understanding different types of colored noise in audio production

The word “noise” often has a negative connotation – anything that interferes with what we want to hear. A person talking loudly during a movie. Construction noise next door prevents us from sleeping in silence. The noise floor of a piece of gear inferring with a quiet part of a mix. 

We can also think of noise as a good thing. White noise machines help us sleep, and pink noise sweeps can be used for acoustic testing. These different types of noise are called colored noise, an analogy to the visual color spectrum. The colors are analogous to the sonic timbres that are generated by different filters on spectral content.

In this article, we’ll talk a bit about different colors of noise, and different colored noise uses in audio production.

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Different types of colored noise 

White noise is random noise generated with equal intensity across the spectrum from 20 Hz–20 kHz. White noise can sound very harsh since the intensity of every frequency band is the same as the next. To achieve different colors of noise, filters are applied to the white noise to give it a specific sound.

Besides white noise, pink noise is the most common “color” of noise. Pink noise is filtered white noise with equal energy per octave of frequency. It is closer to mimicking the human auditory system. It sounds more equal across all frequencies.

White noise is better at masking sounds as the intensity of every frequency is equal across all the noise – but pink noise is more pleasant to listen to. Pink noise is also helpful in audio testing situations due the frequency response mimicking our own hearing. The density per frequency interval (in the case of pink noise, the interval is per octave) is inversely proportional to the frequency of the signal. 

Pink noise has equal energy per octave of frequency, and a roll off about 3 dB per octave as frequency increases. 

Besides pink noise and white noise, there are other “colors” of noise that have found use in helping us relax, sleep, or help create a sonic landscape in music or sound design.

Brown noise is not really named after a color, but rather the randomized motion of particles suspended in a fluid, called Brownian motion after scientist Robert Brown, who in the early 1800s described the phenomenon but was unable to fully explain it (Einstein later defined it more fully on the topic). Brown noise is the signal noise that this motion causes. Spectral density is inversely proportional to f ² which means the lower frequencies are augmented, and slope is more severe than in pink noise.

There’s been more recent public interest in brown noise as very helpful for focus and attention, particularly for those with ADHD. 

Other “colors of noise exist, including blue noise, violet noise, and grey noise.

Blue noise as a spectral density inversely proportional to pink noise. It increases 3 dB per octave with increasing frequency. It has minimal low frequency content. This makes it suitable for dithering in visual and audio applications. Its pattern is relatively uniform and random, which lessens digital artifacts and minimizes spikes of information.

Violet noise has a density of an increase of 6 dB per octave over increasing frequency. Violet noise was used in early adaptations of dither. Grey noise has an equal loudness contour so that all frequencies have the same loudness, as opposed to all having the same intensity (like in white noise). It is helpful in testing hearing, as well easing the symptoms of tinnitus.

Using colored noise in audio production

There are some interesting uses for noise beyond helping us relax, or for computing purposes. 

You can use white noise to create effects that will enhance your mix. This article about white noise, filters, and effects gives some great examples for enhancing the rhythm and mood of your music. By utilizing oscillators to create white noise sweeps, or adding white noise at a low level to create a bit of ambiance for a singular instrument, you can fill out your mix with more interesting textures.

There are discussions on the internet that talk about using white noise for the sidechain of a compressor…there isn’t, in my opinion, much of a point for that. It would be much more beneficial to utilize another sound source, like a kick drum, for that. As an aside, if you need a refresher on sidechain compression, here’s a great article that explains what sidechain compression is.

Another way to utilize noise is to build soundscapes where noise enhances the scene. In the example below, brown noise was added to a seascape sound to add low frequency content, more of which might help elevate the sound design of a scene.

In iZotope RX, the De-ess module allows for two kinds of de-essing. One is more “traditional” de-essing, where gain reduction of sibilance is applied above a certain frequency threshold.

The other module allows for spectral shaping, which is a more of an intelligent way to shape frequency content. Spectral Tilt gives you the flexibility to determine what the ideal shape of your high frequency signal could be. Moving the shape towards brown noise provides a darker result, and moving it closer to white noise provides a brighter result. 

In this example, I wanted to remove some of the harshest ess sounds without darkening the overall sound of the mix.

And here's just the ess sounds isolated. 

The Signal Generator module in RX is another feature that uses colored noise. The Signal Generator is able to synthesize silence, tones, and noise. This is useful for creating test tones, calibration tones for post production delivery specs, repairing DC offset, and even using it as a “bleep” module to eliminate obscenities in a dialogue edit.

Using noise for measurement

Pink noise is commonly used to calibrate speakers and test audio systems. Pink noise more resembles our own hearing in terms of intensity and when combined it is easier to discern differences in level simply with our ears vs. white noise. 

Monitor calibration levels for a mixing room can vary - a correctly calibrated room usually has a reference level between 82 dB and 85 dB, depending on the size of the room. Film/TV and Stereo/multi-channel guidelines can vary. If your room is smaller, you might want to aim even a little lower than 82-85 dB. Flatten your setup – no room EQs, any sort of compression, limiting, compensation for sonic “oddities” you feel might exist.

You will first need an SPL meter set up in the listening position (but point the mic towards the ceiling! Most SPL meters are meant to be used in that way). Set monitor level to unity, and play pink noise through each speaker individually and adjust the output of your system until each speaker registers within range using C-weighting. If you’re like me and pink noise gets fatiguing at louder levels - put in some ear plugs when you are measuring!

Once this step is over, you can move on to tuning your room with full spectrum sine sweeps, which will help you determine where the dips and peaks are in the frequency response of the room. This can be done with a microphone and a room acoustic analyzer such as REW, FuzzMeasure, Sonarworks, etc. Then you’re ready to start tackling any acoustic issues and get your room sounding as good as possible!

Start using colored noise in audio production

Colored noise can be used in different ways in audio production, including spectral shaping, layering of noise in a bed for creating richer soundscapes, and in speaker calibration and other acoustic testing purposes. To experiment with colored noise in your productions, demo RX for free and discover what spectral shaping and sound design capabilities you can harness with different colored noise profiles.

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All spectrographs of noise in this article are referenced from https://en.wikipedia.org/wiki/Colors_of_noise – Credit: Warrakkk via Wikimedia Commons (CC BY-SA 3.0)