1/f noise is a signal or process with a frequency spectrum such that the spectral energy density is proportional to the reciprocal of the frequency. 1/f noise, sometimes pronounced as one over f noise, is also called pink noise or flicker noise.
In particular, there is equal energy in all octaves. In terms of power at a constant bandwidth, 1/f noise falls off at 3dB per octave.
1/f noise is found in a wide variety of physical phenomena. Examples include electronic devices, financial markets, astronomy, and human coordination.
The human auditory system, which uses a roughly logarithmic concept of frequency approximated by the Bark scale, does not perceive with equal sensitivity all audible frequencies. However, humans may still differentiate between white and pink noise with ease.
Graphic equalizers also divide signals into bands logarithmically and report power by octaves; audio engineers put pink noise through a system to test whether it has a flat frequency response in the useful spectrum.
White noise is noise in which the intensity of the power spectral density is constant and independent of frequency.
Pink noise is the common name given to 1/f noise which crops up in many natural stochastic processes and approximates the power spectrum of music signals too.
"flickernoise" or "1/f noise") is halfway between white noise and red noise.
This type of noise is common, even in the highest quality oscillators, because in order to bring the signal amplitude up to a usable level, amplifiers are used after the signal source.
Flicker PM can be reduced with good low-noise amplifier design (e.g., using rf negative feedback) and hand-selecting transistors and other electronic components.
This noise can be kept at a very low value with good amplifier design, hand-selected components, the addition of narrowband filtering at the output, or increasing, if feasible, the power of the primary frequency source.
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