Noise

There are various signification of the word "noise".

In the audible range, we can say that noise is sound that is often loud, unexpected and usually unpleasant and undesired.

e.g. street noise, airplan noise, noise from the neighbors...

-"Did you hear that noise in the motor?"

-"Are you joking? Every running motor makes noise!"

- "Yes but don't you hear that "click-click" noise? This shouldn't be..."

In a studio or other listening area we usually try to prevent outside noise to find its way in by having good separation (soundproofing) between outside and inside the room.

Inside generated noise will have to be treated separately (absorption).

Note that the same measure that keeps the noise from entering also keeps the sound from going out. Usually.

For technical measurements (e.g. for Reverberation time measurement) we sometimes use sounds that contains oscillations on many frequencies at the same time, covering the whole frequency range, with randomly varying amplitudes. This is called white noise or pink noise.

What is the difference between white noise and pink noise?

White noise has oscillations at every frequency on a linear scale,

that is as much energy between 100Hz and 200Hz than between 3000Hz and 3100Hz.

Pink noise has oscillations at every frequency on a logarithmic scale,

that is as much energy between 100Hz and 200Hz than between 3000Hz and 6000Hz.

Listen to these 10 seconds examples of white and pink noise.

The "Mono" examples have the same signal on left and right whereas the "Stereo" examples have different signals on left and right (uncorrelated).

White noise Mono

White noise Stereo

Pink noise Mono

Pink noise Stereo