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Impulse Noise (audio)
Impulse noise is a category of (acoustic) noise which includes unwanted, almost instantaneous (thus impulse-like) sharp sounds (like clicks and pops). Noises of the kind are usually caused by electromagnetic interference, scratches on the recording disks, gunfire, explosions and ill synchronization in digital recording and communication. High levels of such a noise (200+ decibels) may damage internal organs, while 180 decibels are enough to destroy or damage human ears. An impulse noise filter can be used to enhance the quality of noisy signals, in order to achieve robustness in pattern recognition and adaptive control systems. A classic filter used to remove impulse noise is the median filter, at the expense of signal degradation
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Architectural Acoustics
Architectural acoustics
Architectural acoustics
(also known as room acoustics and building acoustics) is the science and engineering of achieving a good sound within a building and is a branch of acoustical engineering.[1] The first application of modern scientific methods to architectural acoustics was carried out by Wallace Sabine
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Crackling Noise
Crackling noise
Crackling noise
arises when a system is subject to an external force and it responds via events that appear very similar at many different scales. In a classical system there are usually two states, on and off. However, sometimes a state can exist in between. There are three main categories this noise can be sorted into: the first is popping where events at very similar magnitude occur continuously and randomly, e.g. popcorn; the second is snapping where there is little change in the system until a critical threshold is surpassed, at which point the whole system flips from one state to another, i.e. snapping a pencil; the third is crackling which is a combination of popping and snapping, where there are some small and some large events with a relation law predicting their occurrences, referred to as universality.[1] Crackling can be observed in many natural phenomena, e.g
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Acoustics
Acoustics
Acoustics
is the branch of physics that deals with the study of all mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer. The application of acoustics is present in almost all aspects of modern society with the most obvious being the audio and noise control industries. Hearing
Hearing
is one of the most crucial means of survival in the animal world, and speech is one of the most distinctive characteristics of human development and culture. Accordingly, the science of acoustics spreads across many facets of human society—music, medicine, architecture, industrial production, warfare and more
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Noise Control
Noise control
Noise control
or noise mitigation is a set of strategies to reduce noise pollution or to reduce the impact of that noise, whether outdoors or indoors.Contents1 Overview 2 Approaches to Noise Control2.1 Source 2.2 Path 2.3 Receiver3 Basic technologies 4 Roadways 5 Aircraft 6 Architectural solutions6.1 Materials7 Industrial 8 Commercial 9 Urban planning 10 See also 11 References 12 External linksOverview[edit] The main areas of noise mitigation or abatement are: transportation noise control, architectural design, urban planning through zoning codes,[1] and occupational noise control. Roadway noise
Roadway noise
and aircraft noise are the most pervasive sources of environmental noise
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Phase Distortion
In signal processing, phase distortion or phase-frequency distortion is distortion, that is, change in the shape of the waveform, that occurs when (a) a filter's phase response is not linear over the frequency range of interest, that is, the phase shift introduced by a circuit or device is not directly proportional to frequency, or (b) the zero-frequency intercept of the phase-frequency characteristic is not 0 or an integral multiple of 2π radians. Audibility of phase distortion[edit] Grossly changed phase relationships, without changing amplitudes, can be audible but the degree of audibility of the type of phase shifts expected from typical sound systems remains debated.[1][2][3] See also[edit]Audio system measurements Phase noiseReferences[edit]^ Arthur C Ludwig Sr. (1997). "Audibility of Phase Distortion". Retrieved 15 February 2016.  ^ Lipshitz, Stanley P.; Pocock, Mark; Vanderkooy, John (1 September 1982)
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Gaussian Noise
Gaussian noise
Gaussian noise
is statistical noise having a probability density function (PDF) equal to that of the normal distribution, which is also known as the Gaussian distribution.[1][2] In other words, the values that the noise can take on are Gaussian-distributed. The probability density function p displaystyle p of a Gaussian random variable z displaystyle z is given by: p G ( z ) = 1 σ 2 π
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Record Restoration
Record restoration, a particular kind of audio restoration, is the process of converting the analog signal stored on gramophone records (either 78 rpm shellac, or 45 and 33⅓ rpm vinyl) into digital audio files that can then be edited with computer software and eventually stored on a hard-drive, recorded to digital tape, or burned to a CD or DVD. The process may be divided into several separate steps performed in the following order: 1. Cleaning the record, to prevent unwanted audio artefacts from being introduced in the capture that will necessitate correction in the digital domain (e.g. transient surface noise caused by dirt), and to prevent unnecessary wear and damage to the stylus used in playback. 2. Transcription of the record to another format on another medium (generally a digital format such as a wav file on a computer); 3
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Audio Synchronizer
An audio synchronizer is a variable audio delay used to correct or maintain audio-video sync or timing[1] also known as lip sync error. See for example the specification for audio to video timing given in ATSC
ATSC
Document IS-191.[2] Modern television systems use large amounts of video signal processing such as MPEG
MPEG
preprocessing, encoding and decoding, video synchronization and resolution conversion in pixelated displays. This video processing can cause delays in the video signal ranging from a few microseconds to tens of seconds. If the television program is displayed to the viewer with this video delay the audio-video synchronization is wrong, and the video will appear to the viewer after the sound is heard
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Pink Noise
Pink noise
Pink noise
or ​1⁄f noise is a signal or process with a frequency spectrum such that the power spectral density (energy or power per frequency interval) is inversely proportional to the frequency of the signal. In pink noise, each octave (halving/doubling in frequency) carries an equal amount of noise energy. The name arises from the pink appearance of visible light with this power spectrum.[1] This is in contrast with white noise which has equal intensity per frequency interval. Within the scientific literature the term pink noise is sometimes used a little more loosely to refer to any noise with a power spectral density of the form S ( f ) ∝ 1 f α , displaystyle S(f)propto frac 1 f^ alpha , where f is frequency, and 0 < α < 2, with exponent α usually close to 1
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Median Filter
The median filter is a nonlinear digital filtering technique, often used to remove noise from an image or signal. Such noise reduction is a typical pre-processing step to improve the results of later processing (for example, edge detection on an image). Median
Median
filtering is very widely used in digital image processing because, under certain conditions, it preserves edges while removing noise (but see discussion below), also having applications in signal processing.Contents1 Algorithm description 2 Worked 1D example 3 Boundary issues 4 2D median filter pseudo code 5 Algorithm implementation issues 6 Edge preservation properties 7 See also 8 References 9 External linksAlgorithm description[edit] The main idea of the median filter is to run through the signal entry by entry, replacing each entry with the median of neighboring entries. The pattern of neighbors is called the "window", which slides, entry by entry, over the entire signal
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Decibel
The decibel (symbol: dB) is a unit of measurement used to express the ratio of one value of a physical property to another on a logarithmic scale. It can be used to express a change in value (e.g., +1 dB or −1 dB) or an absolute value. In the latter case, it expresses the ratio of a value to a reference value; when used in this way, the decibel symbol should be appended with a suffix that indicates the reference value or some other property. For example, if the reference value is 1 volt, then the suffix is "V" (e.g, "20 dBV"), and if the reference value is one milliwatt, then the suffix is "m" (e.g., "20 dBm").[1] There are two different scales used when expressing a ratio in decibels depending on the nature of the quantities: field, power, and root-power
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Gunfire
A gunshot is a single discharge of a gun, typically a man-portable firearm, producing a visible flash, a powerful and loud shockwave and often chemical gunshot residue. The term can also refer to a ballistic wound caused by such a discharge. Multiple discharges of one or more firearms are referred to as gunfire. The word can connote either the sound of a gun firing, the projectiles that were fired, or both. For example, the statement "gunfire came from the next street" could either mean the sound of discharge, or it could mean the bullets that were discharged. It is better to be a bit more specific while writing however. "The sound of gunfire" or "we came under gunfire" would be more descriptive and prevent confusion. In the latter phrase, in particular, "fire" is more commonly used (i.e
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Electromagnetic Interference
Electromagnetic interference
Electromagnetic interference
(EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction.[1] The disturbance may degrade the performance of the circuit or even stop it from functioning. In the case of a data path, these effects can range from an increase in error rate to a total loss of the data.[2] Both man-made and natural sources generate changing electrical currents and voltages that can cause EMI: ignition systems, cellular network of mobile phones, lightning, solar flares, and auroras (Northern/Southern Lights)
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Impulse Function
In mathematics, the Dirac delta function, or δ function, is a generalized function, or distribution that was historically introduced by the physicist Paul Dirac
Paul Dirac
for modelling the density of an idealized point mass or point charge, as a function that is equal to zero everywhere except for zero and whose integral over the entire real line is equal to one.[1][2][3] As there is no function that has these properties, the computations that were done by the theoretical physicists appeared to mathematicians as nonsense, until the introduction of distributions by Laurent Schwartz, for formalizing and validating mathematically these computations
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Gradient Noise
Gradient noise is a type of noise commonly used as a procedural texture primitive in computer graphics. It is conceptually different[further explanation needed], and often confused with value noise. This method consists of a creation of a lattice of random (or typically pseudorandom) gradients, dot products of which are then interpolated to obtain values in between the lattices. An artifact of some implementations of this noise is that the returned value at the lattice points is 0. Unlike the value noise, gradient noise has more energy in the high frequencies. The first known implementation of a gradient noise function was Perlin noise, credited to Ken Perlin, who published the description of it in 1985. [1] Later developments were Simplex noise and OpenSimplex noise.References[edit]^ David Ebert, Kent Musgrave, Darwyn Peachey, Ken Perlin, and Worley. Texturing and Modeling: A Procedural Approach. Academic Press, October 1994
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