In signal processing, noise is a general term for unwanted (and, in general, unknown) modifications that a signal may suffer during capture, storage, transmission, processing, or conversion.[1]
Sometimes the word is also used to mean signals that are random (unpredictable) and carry no useful information; even if they are not interfering with other signals or may have been introduced intentionally, as in comfort noise.
Noise reduction, the recovery of the original signal from the noise-corrupted one, is a very common goal in the design of signal processing systems, especially filters. The mathematical limits for noise removal are set by information theory.
Types of noise[edit]
Signal processing noise can be classified by its statistical properties (sometimes called the "color" of the noise) and by how it modifies the intended signal:
- Additive noise, gets added to the intended signal
- White noise
- Black noise
- Gaussian noise
- Pink noise or flicker noise, with 1/f power spectrum
- Brownian noise, with 1/f2 power spectrum
- Contaminated Gaussian noise, whose PDF is a linear mixture of Gaussian PDFs
- Power-law noise
- Cauchy noise
- Multiplicative noise, multiplies or modulates the intended signal
- Quantization error, due to conversion from continuous to discrete values
- Poisson noise, typical of signals that are rates of discrete events
- Shot noise, e.g. caused by static electricity discharge
- Transient noise, a short pulse followed by decaying oscillations
- Burst noise, powerful but only during short intervals
- Phase noise, random time shifts in a signal
Noise in specific kinds of signals[edit]
Noise may arise in signals of interest to various scientific and technical fields, often with specific features:
- Noise (audio), such as "hiss" or "hum", in audio signals
- Background noise, due to spurious sounds during signal capture
- Comfort noise, added to voice communications to fill silent gaps
- Electromagnetically induced noise, audible noise due to electromagnetic vibrations in systems involving electromagnetic fields
- Noise (video), such as "snow"
- Noise (radio), such as "static", in radio transmissions
- Image noise, affects images, usually digital ones
- Salt and pepper noise or spike noise, scattered very dark or very light pixels
- Fixed pattern noise, that is tied to pixel sensors
- Shadow noise, made visible by increasing brightness or contrast
- Speckle noise, typical of radar imaging and interferograms
- Film grain in analog photography
- Compression artifacts or "mosquito noise" around edges in JPEG and other formats
- Noise (electronics) in electrical signals
- Johnson–Nyquist noise, in semiconductors
- Quantum noise
- Quantum 1/f noise, a disputed theory about quantum systems
- Generation-recombination noise, in semiconductor devices
- Oscillator phase noise, random fluctuations of the phase of an oscillator
- Barkhausen effect or Barkhausen noise, in the strength of a ferromagnet
- Spectral splatter or switch noise, caused by on/off transmitter switching
- Ground noise, appearing at the ground terminal of audio equipment
- Synaptic noise, observed in neuroscience
- Neuronal noise, observed in neuroscience
- Transcriptional noise in the transcription of genes to proteins
- Cosmic noise, in radioastronomy
- Phonon noise in materials science
- Internet background noise, packets sent to unassigned or inactive IP addresses
- Fano noise, in particle detectors
- Mode partition noise in optical cables
- Seismic noise, spurious ground vibrations in seismology
- Cosmic microwave background, microwave noise left over from the Big Bang
Measures of noise in signals[edit]
A long list of noise measures have been defined to measure noise in signal processing: in absolute terms, relative to some standard noise level, or relative to the desired signal level. They include:
- Dynamic range, often defined by inherent noise level
- Signal-to-noise ratio (SNR), ratio of noise power to signal power
- Peak signal-to-noise ratio, maximum SNR in a system
- Signal to noise ratio (imaging), for images
- Carrier-to-noise ratio, the signal-to-noise ratio of a modulated signal
- Noise power
- Noise figure
- Noise-equivalent flux density, a measure of noise in astronomy
- Noise floor
- Noise margin, by how much a signal exceeds the noise level
- Reference noise, a reference level for electronic noise
- Noise spectral density, noise power per unit of bandwidth
- Noise temperature
- Effective input noise temperature
- Noise-equivalent power, a measure of sensitivity for photodetectors
- Relative intensity noise, in a laser beam
- Antenna noise temperature, measure of noise in telecommunications antenna
- Received noise power, noise at a telecommunications receiver
- Circuit noise level, ratio of circuit noise to some reference level
- Channel noise level, some measure of noise in a communication channel
- Noise-equivalent target, intensity of a target when the signal-to-noise level is 1[2]
- Equivalent noise resistance, a measure of noise based on equivalent resistor
- Carrier-to-receiver noise density, ratio of received carrier power to receiver noise
- Carrier-to-noise-density ratio,
- Spectral signal-to-noise ratio
- Antenna gain-to-noise temperature, a measure of antenna performance
- Contrast-to-noise ratio, a measure of image quality
- Noise print, statistical signature of ambient noise for its suppression
- Equivalent pulse code modulation noise, measure of noise by comparing to PCM quantization noise
Technology for noise in signals[edit]
Almost every technique and device for signal processing has some connection to noise. Some random examples are:
- Noise shaping
- Antenna analyzer or noise bridge, used to measure the efficiency of antennas
- Noise gate
- Noise generator, a circuit that produces a random electrical signal
- Radio noise source used to calibrate radiotelescopes
- Friis formulas for the noise in telecommunications
- Noise-domain reflectometry, uses existing signals to find cable faults
- Noise-immune cavity-enhanced optical heterodyne molecular spectroscopy
See also[edit]
- Anti-information
- Noise (electronics)
- Signal-to-noise statistic, a mathematical formula to measure the difference of two values relative to their standard deviations
References[edit]
- ^ Vyacheslav Tuzlukov (2010), Signal Processing Noise, Electrical Engineering and Applied Signal Processing Series, CRC Press. 688 pages. ISBN 9781420041118
- ^ Viviana Vladutescu, Daniela. "Systems Engineering for Space Based Applications" (PDF). www.ieee.li. CAS IEEE Long Island Section. Retrieved 26 March 2023.
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