White, pink, brown, blue… These are just some of the rainbow of colours that are used to describe particular shades of noise. But why colours? And what is the difference between a pink noise and a white noise? Does it even matter?

These are all questions that clients have asked us, especially when coming to us with a request for “white noise”. As you can read in a previous blog post, that’s not what we sell here at Soundmask.

Why colours?

The colours of noise are named based on their spectral properties, similar to the way light waves are split into colours. But light waves and sound waves are not exactly analogous. For example, while light waves are electromagnetic waves, sound waves are mechanical waves. Further, while light waves are visible to the eye, sound waves are invisible to the human eye. That’s why drawing a graph of the colours of noise will not look the same as a graph of the colours of light.

How many colours of noise are there?

It feels like every year or so, we hear of another colour of noise coined by (I suspect) someone in a government lab somewhere. Or maybe the marketing department adjacent to said lab. This is because the American National Standard T1.523-2001, Telecom Glossary 2000. defines white, pink, blue, and black noise. How, you might ask? Let’s explore them.

Here are the definitions from the glossary along with sound samples for each:

White noise

White noise definition:

“Noise having a frequency spectrum that is continuous and uniform over a specified frequency band. Note: White noise has equal power per hertz over the specified frequency band. Synonym additive white gaussian noise.“

Here’s a sample:

You can hear it’s quite an annoying hissing sound, which is why you cannot conflate sound masking and white noise — sound masking should never be annoying!

Pink noise

Pink noise definition: “In acoustics, noise in which there is equal power per octave.”

Here’s a sample:

You can hear that pink noise is a more comfortable sound, with more “bottom end” compared with white noise.

Blue noise

Blue noise definition:

“In a spectrum of frequencies, a region in which the spectral density, i.e., power per hertz, is proportional to the frequency.”

Here’s a sample:

This is even more annoying than white noise, in my opinion. High pitched hissing.

Black noise

Black noise definition:

“Noise that has a frequency spectrum of predominately zero power level over all frequencies except for a few narrow bands or spikes. 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. Thus, in the time domain, a few random pulses occur while scanning.”

Essentially it sounds like “nothing”.

But that’s not all!

I have heard of brown noise (very low frequency), red noise (between pink and brown noise), violet noise (not to be confused with violent noise), and a combination of all of the above.

Different colours of noise have different purposes. For example, laboratories often use white noise as a neutral background sound for testing. Pink noise is often used as a sleep aid.

So there you have it. A crash course in the colours of noise. What about Soundmask’s sound spectrum? We haven’t named the colour, but you can listen to a sample overlaid in part of our promo video here.

Sound samples courtesy of audiocheck.net