What noise annoys an oyster? A noisy noise annoys an oyster!
Now we’ve established that, let’s turn our attention to another important question: what’s the difference between white, pink and brown noise? These different flavours of noise are separate and distinct concepts; yes, they’re all noisy and annoying, but they’re differently noisy and annoying in important ways. You may be familiar with white noise as the telly static sound effect, which is all well and good if you’re David Lynch making an episode of Twin Peaks, but pink noise often has more practical utility to a sound engineer, particularly in calibrating audio equipment, and who doesn’t love a well-calibrated audio system?
White noise is the name given to noise consisting of equal energy per frequency, while pink noise is equal energy per octave. But what does that even mean? Well, let’s take a moment to ponder our perception of sound.
When a note jumps up an octave we perceive that as a sound that’s twice as high as the original. For example, the note A4 has a frequency of 440 Hz, and A5 has a frequency of 880 Hz; the octave has increased by 1, while the number of frequencies has doubled. On a keyboard this is represented as an equal distribution of keys across each octave; 12 notes = 1 octave.
But herein lies the ambiguity – the difference between A4 and A5 is 440 Hz, but the difference between A5 and A6 is 880 Hz, and the difference between A6 and A7 is 1,760 Hz. With every increment of one octave, the number of frequencies doubles.
White noise is randomly generated noise across the entire frequency spectrum, so each individual frequency gets an equal blast. The problem is, as we’ve just discovered, this creates an imbalance in our perception, because is takes more frequencies to get you from A6 to A7 than it does to get you from A1 to A2. This means that the resulting noise will be skewed towards the top end of the frequency spectrum, and thus sound overly trebly.
This is where pink noise comes in. Pink noise distributes the energy according to how we hear, so you get equal energy per octave, rather than per frequency, resulting in a more “natural” sounding annoying noise. This is why audio engineers will use pink noise to calibrate their systems, for example by playing back pink noise through their speakers and using a reference mic + spectrum analyser to measure the frequency response at a given location.
So what about brown noise?
Well, brown noise is the name given to noise that has disproportionately higher intensity at lower frequencies, not dissimilar to waves on a beach. It has little practical application in audio calibration, however it is rather pleasing to listen to and has been said to be a useful sleep aid. Just be careful that it doesn’t make you shit yourself.
Have a listen to the different flavours of noise below: