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Examples of electrical noise-level measurement units are dBu, dBm0, dBrn, dBrnC, and dBrn(f 1 − f 2), dBrn(144-line). Noise may also be characterized by its probability distribution and noise spectral density N 0 (f) in watts per hertz. A noise signal is typically considered as a linear addition to a useful information signal.
Johnson–Nyquist noise (thermal noise, Johnson noise, or Nyquist noise) is the electronic noise generated by the thermal agitation of the charge carriers (usually the electrons) inside an electrical conductor at equilibrium, which happens regardless of any applied voltage.
Brownian noise or "brown" noise, with spectral density inversely proportional to the square of frequency; Pseudorandom noise, in cryptography, artificial signal that can pass for random; Statistical noise, a colloquialism for recognized amounts of unexplained variation in a sample; Shot noise, noise which can be modeled by a Poisson process
These phenomena can potentially generate vibrations of the ferromagnetic, conductive parts, coils and permanent magnets of electrical, magnetic and electromechanical device, resulting in an audible sound if the frequency of vibrations lies between 20 Hz and 20 kHz, and if the sound level is high enough to be heard (e.g. large surface of ...
The noise power at the output of the amplifier chain consists of four parts: The amplified noise of the source The output referred noise of the first amplifier amplified by the second and third amplifier ()
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Aeroacoustics is the study of noise generated by air movement, for instance via turbulence, and the movement of sound through the fluid air. This knowledge was applied in the 1920s and '30s to detect aircraft before radar was invented and is applied in acoustical engineering to study how to quieten aircraft .