Pink noise
Pink noise, 1⁄f noise, fractional noise or fractal noise is a signal or process with a frequency spectrum such that the power spectral density (power per frequency interval) is inversely proportional to the frequency of the signal. In pink noise, each octave interval (halving or doubling in frequency) carries an equal amount of noise energy.
"Fractal noise" redirects here. For the novel, see Fractal Noise.
Pink noise sounds like a waterfall.[2] It is often used to tune loudspeaker systems in professional audio.[3] Pink noise is one of the most commonly observed signals in biological systems.[4]
The name arises from the pink appearance of visible light with this power spectrum.[5] This is in contrast with white noise which has equal intensity per frequency interval.
Audio testing[edit]
Pink noise is commonly used to test the loudspeakers in sound reinforcement systems, with the resulting sound measured with a test microphone in the listening space connected to a spectrum analyzer[3] or a computer running a real-time fast Fourier transform (FFT) analyzer program such as Smaart. The sound system plays pink noise while the audio engineer makes adjustments on an audio equalizer to obtain the desired results. Pink noise is predictable and repeatable, but it is annoying for a concert audience to hear. Since the late 1990s, FFT-based analysis enabled the engineer to make adjustments using pre-recorded music as the test signal, or even the music coming from the performers in real time.[61] Pink noise is still used by audio system contractors[62] and by computerized sound systems which incorporate an automatic equalization feature.[63]
In manufacturing, pink noise is often used as a burn-in signal for audio amplifiers and other components, to determine whether the component will maintain performance integrity during sustained use.[64] The process of end-users burning in their headphones with pink noise to attain higher fidelity has been called an audiophile "myth".[65]