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Signal processing
 
 
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Signal processing is the analysis, interpretation, and manipulation of signals. Signals of interest include: sound
Audio signal processing

Audio signal processing, sometimes referred to as audio processing, is the intentional alteration of sound Signal , or sound. As audio signals may be electronically represented in either digital or analog signal format, signal processing may occur in either domain....
, images
Image processing

In electrical engineering and computer science, image processing is any form of signal processing for which the input is an , such as photographs or video frame; the output of image processing can be either an image or a set of characteristics or parameters related to the image....
, time-varying measurement values and sensor
Sensor

A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube....
 data, for example biological data such as electrocardiogram
Electrocardiogram

An electrocardiogram is a recording of the electricity activity of the heart over time produced by an electrocardiograph, usually in a Non-invasive recording via skin electrodes....
s, control system
Control system

A control system is a device or set of devices to manage, command, direct or regulate the behavior of other devices or systems.There are two common classes of control systems, with many variations and combinations: logic gate, and feedback or linear controls....
 signals, telecommunication transmission
Transmission

Transmission is the act of passing something on.Specifically, it may refer to:*Transmission , a gear system transmitting mechanical power, as in a car...
 signals such as radio signals, and many others.

Processing of such signals includes: filtering
Electronic filter

Electronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal and/or to enhance wanted ones....
 (for example in tone controls, equalizers
Equalization filter

An equalization filter is a filter , usually adjustable, chiefly meant to compensate for the unequal frequency response of some other signal processing circuit or system....
 and image enhancement software), adaptive filter
Adaptive filter

An adaptive filter is a filter that self-adjusts its transfer function according to an optimizing algorithm. Because of the complexity of the optimizing algorithms, most adaptive filters are digital filters that perform digital signal processing and adapt their performance based on the input signal....
ing (for example for echo-cancellation in a conference telephone, or separation of information from noise
Noise

In common use, the word noise means unwanted sound or noise pollution. In electronics noise can refer to the electronic signal corresponding to acoustic noise or the electronic signal corresponding to the noise commonly seen as 'Noise ' on a degraded television or video image....
 for aircraft identification by radar), compression
Data compression

In computer science and information theory, data compression or source coding is the process of encoding information using fewer bits than an code representation would use through use of specific encoding schemes....
 (for example, image compression
Image compression

Image compression is the application of Data compression on digital images. In effect, the objective is to reduce redundancy of the image data in order to be able to store or data transmission data in an efficient form....
) and feature extraction
Feature extraction

In pattern recognition and in , Feature extraction is a special form of dimensionality reduction.When the input data to an algorithm is too large to be processed and it is suspected to be notoriously redundant then the input data will be transformed into a reduced representation set of features ....
 (for example speech-to-text
Speech recognition

Speech recognition converts spoken words to machine-readable input . The term "voice recognition" is sometimes incorrectly used to refer to speech recognition, when actually referring to speaker recognition, which attempts to identify the person speaking, as opposed to what is being said....
 conversion), spectrum analysis
Spectrum analyzer

A spectrum analyzer or spectral analyzer is a device used to examine the spectral composition of some electricity, acoustics, or optics waveform....
 (for example in magnetic resonance imaging
Magnetic resonance imaging

GaneshMagnetic resonance imaging , or nuclear magnetic resonance imaging , is primarily a medical imaging technique most commonly used in radiology to visualize the structure and function of the body....
), wavetable synthesis
Wavetable synthesis

Wavetable synthesis is a technique used in certain digital music synthesizers to implement a restricted form of real-time additive synthesis. The technique was first developed by Wolfgang Palm of Palm_Products_GmbH in the late 1970s, and has since been used in various forms in other synthesizers built by Sequential Circuits, Ensoniq, Yamaha,...
 (in modem
Modem

Modem is a peripheral device that modulation an analog carrier wave Signal to encode digital information, and also demodulation such a carrier signal to decode the transmitted information....
s and music synthesizer
Synthesizer

A synthesizer is an electronic instrument capable of producing a variety of sounds by generating and combining signals of different frequency....
s), storage, digitalization and reconstruction.

Signals are electrical representations of time-varying or spatial-varying physical quantities, either analog or digital, and may come from various sources.






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Signal processing is the analysis, interpretation, and manipulation of signals. Signals of interest include: sound
Audio signal processing

Audio signal processing, sometimes referred to as audio processing, is the intentional alteration of sound Signal , or sound. As audio signals may be electronically represented in either digital or analog signal format, signal processing may occur in either domain....
, images
Image processing

In electrical engineering and computer science, image processing is any form of signal processing for which the input is an , such as photographs or video frame; the output of image processing can be either an image or a set of characteristics or parameters related to the image....
, time-varying measurement values and sensor
Sensor

A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube....
 data, for example biological data such as electrocardiogram
Electrocardiogram

An electrocardiogram is a recording of the electricity activity of the heart over time produced by an electrocardiograph, usually in a Non-invasive recording via skin electrodes....
s, control system
Control system

A control system is a device or set of devices to manage, command, direct or regulate the behavior of other devices or systems.There are two common classes of control systems, with many variations and combinations: logic gate, and feedback or linear controls....
 signals, telecommunication transmission
Transmission

Transmission is the act of passing something on.Specifically, it may refer to:*Transmission , a gear system transmitting mechanical power, as in a car...
 signals such as radio signals, and many others.

Processing of such signals includes: filtering
Electronic filter

Electronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal and/or to enhance wanted ones....
 (for example in tone controls, equalizers
Equalization filter

An equalization filter is a filter , usually adjustable, chiefly meant to compensate for the unequal frequency response of some other signal processing circuit or system....
 and image enhancement software), adaptive filter
Adaptive filter

An adaptive filter is a filter that self-adjusts its transfer function according to an optimizing algorithm. Because of the complexity of the optimizing algorithms, most adaptive filters are digital filters that perform digital signal processing and adapt their performance based on the input signal....
ing (for example for echo-cancellation in a conference telephone, or separation of information from noise
Noise

In common use, the word noise means unwanted sound or noise pollution. In electronics noise can refer to the electronic signal corresponding to acoustic noise or the electronic signal corresponding to the noise commonly seen as 'Noise ' on a degraded television or video image....
 for aircraft identification by radar), compression
Data compression

In computer science and information theory, data compression or source coding is the process of encoding information using fewer bits than an code representation would use through use of specific encoding schemes....
 (for example, image compression
Image compression

Image compression is the application of Data compression on digital images. In effect, the objective is to reduce redundancy of the image data in order to be able to store or data transmission data in an efficient form....
) and feature extraction
Feature extraction

In pattern recognition and in , Feature extraction is a special form of dimensionality reduction.When the input data to an algorithm is too large to be processed and it is suspected to be notoriously redundant then the input data will be transformed into a reduced representation set of features ....
 (for example speech-to-text
Speech recognition

Speech recognition converts spoken words to machine-readable input . The term "voice recognition" is sometimes incorrectly used to refer to speech recognition, when actually referring to speaker recognition, which attempts to identify the person speaking, as opposed to what is being said....
 conversion), spectrum analysis
Spectrum analyzer

A spectrum analyzer or spectral analyzer is a device used to examine the spectral composition of some electricity, acoustics, or optics waveform....
 (for example in magnetic resonance imaging
Magnetic resonance imaging

GaneshMagnetic resonance imaging , or nuclear magnetic resonance imaging , is primarily a medical imaging technique most commonly used in radiology to visualize the structure and function of the body....
), wavetable synthesis
Wavetable synthesis

Wavetable synthesis is a technique used in certain digital music synthesizers to implement a restricted form of real-time additive synthesis. The technique was first developed by Wolfgang Palm of Palm_Products_GmbH in the late 1970s, and has since been used in various forms in other synthesizers built by Sequential Circuits, Ensoniq, Yamaha,...
 (in modem
Modem

Modem is a peripheral device that modulation an analog carrier wave Signal to encode digital information, and also demodulation such a carrier signal to decode the transmitted information....
s and music synthesizer
Synthesizer

A synthesizer is an electronic instrument capable of producing a variety of sounds by generating and combining signals of different frequency....
s), storage, digitalization and reconstruction.

Signals are electrical representations of time-varying or spatial-varying physical quantities, either analog or digital, and may come from various sources. In the context of signal processing, arbitrary binary data streams and on-off signals are not considered as signals, but only analog and digital signals that are representations of analog physical quantities.

In communication systems, signal processing occurs at OSI layer
OSI model

The Open Systems Interconnection Reference Model is an abstract description for layered communications and computer network protocol design. It was developed as part of the Open Systems Interconnection initiative....
 1, the Physical Layer
Physical layer

The Physical Layer is the first and lowest layer in the seven-layer OSI model of computer networking.The Physical Layer comprises the basic hardware transmission technologies of a network....
 (modulation
Modulation

In telecommunications, modulation is the process of varying a Periodic function waveform, i.e. a tone, in order to use that signal to convey a message, in a similar fashion as a musician may modulate the tone from a musical instrument by varying its volume, timing and Pitch ....
, equalization
Equalization

Equalization, equalisation or EQ is the process of using passive or active electronic elements or digital algorithms for the purpose of altering the frequency response characteristics of a system....
, multiplexing
Multiplexing

In telecommunications and computer networks, multiplexing is a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium....
, radio transmission, etc) in the seven layer OSI model, as well as at OSI layer 6, the Presentation Layer
Presentation layer

The Presentation Layer is the sixth layer of the seven-layer OSI model of computer networking.The Presentation Layer is responsible for the delivery and formatting of information to the application layer for further processing or display....
 (source coding, including analog-to-digital conversion
Analog-to-digital converter

An analog-to-digital converter is a device which converts continuous signal to Discrete signal digital numbers. The reverse operation is performed by a digital-to-analog converter ....
 and data compression
Data compression

In computer science and information theory, data compression or source coding is the process of encoding information using fewer bits than an code representation would use through use of specific encoding schemes....
).

Categories of signal processing

  • Analog signal processing
    Analog signal processing

    Analog signal processing is any signal processing conducted on analog signals by analog means. "Analog" indicates something that is mathematically represented as a set of continuous values....
     — for signals that have not been digitized, as in classical radio, telephone, radar, and television systems. This involves linear electronic circuits such as passive filters, active filter
    Active filter

    An active filter is a type of analog electronic filter, distinguished by the use of one or more active components i.e. voltage amplifiers or buffer amplifiers....
    s, additive mixers
    Electronic mixer

    An electronic mixer is a device that combines two or more electronics Signal s into one composite output signal. There are two basic types of mixer....
    , integrator
    Integrator

    An integrator is a device to perform the mathematical operation known as integral, a fundamental operation in calculus.The integration function is often part of engineering, physics, machine, chemical and science calculations....
    s and delay line
    Delay line

    The term delay line has multiple meanings:* In electronics and derivative fields such as telecommunications, a delay line is a device where the input signal reaches the output of the device after a known period of time has elapsed....
    s. It also involves non-linear circuits such as compandors, multiplicators (frequency mixer
    Frequency mixer

    In telecommunications, a mixer is a nonlinear or time-varying electrical network or device that accepts as its input two different frequencies and presents at its output a mixture of signal s at several frequency:...
    s and voltage-controlled amplifiers), voltage-controlled filter
    Voltage-controlled filter

    A voltage-controlled filter is an electronic filter whose operating characteristics can be controlled by means of a control voltage applied to one or more inputs....
    s, voltage-controlled oscillator
    Voltage-controlled oscillator

    A voltage-controlled oscillator or VCO is an electronic oscillator designed to be controlled in oscillation frequency by a voltage input. The frequency of oscillation is varied by the applied DC voltage, while Modulation signals may also be fed into the VCO to cause frequency modulation or phase modulation ; a VCO with digital pulse o...
    s and phase-locked loop
    Phase-locked loop

    A phase-locked loop or phase lock loop is a control system that generates a Signal that has a fixed relation to the phase of a "reference" signal....
    s.
  • Discrete time signal processing — for sampled signals that are considered as defined only at discrete points in time, and as such are quantized in time, but not in magnitude. Analog discrete-time signal processing is a technology based on electronic devices such as sample and hold
    Sample and hold

    In electronics, a sample and hold circuit is used to interface real-world signals, by changing analog signal signals to a subsequent system such as an analog-to-digital converter....
     circuits, analog time-division multiplexer
    Multiplexer

    In electronics, a multiplexer or mux is a device that performs multiplexing; it selects one of many analog or digital input signals and outputs that into a single line....
    s, analog delay line
    Analog delay line

    An analog delay line is a network of electrical components connected in series; where each individual element creates a time difference or phase change between its input signal and its output signal....
    s and analog feedback shift registers. This technology was a predecessor of digital signal processing, see below, and is still used in advanced processing of gigahertz signals. The concept of discrete-time signal processing also refers to a theoretical discipline that establishes a mathematical basis for digital signal processing, without taking quantization error
    Quantization error

    The difference between the actual analog value and quantized digital value due is called quantization error. This error is due either to rounding or truncation....
     into consideration.
  • Digital signal processing
    Digital signal processing

    Digital signal processing is concerned with the representation of the signal s by a sequence of numbers or symbols and the processing of these signals....
     — for signals that have been digitized. Processing is done by general-purpose computer
    Computer

    A computer is a machine that manipulates Data according to a list of Code .The first devices that resemble modern computers date to the mid-20th century , although the computer concept and various machines similar to computers existed earlier....
    s or by digital circuits such as ASIC
    Application-specific integrated circuit

    An application-specific integrated circuit is an integrated circuit customized for a particular use, rather than intended for general-purpose use....
    s, field-programmable gate array
    Field-programmable gate array

    A field-programmable gate array is a semiconductor device that can be configured by the customer or designer after manufacturing—hence the name "field-programmable"....
    s or specialized digital signal processor
    Digital signal processor

    A digital signal processor is a specialized microprocessor designed specifically for digital signal processing, generally in real-time computing....
    s (DSP chips). Typical arithmetical operations include fixed-point
    Fixed-point arithmetic

    In computing, a fixed-point number representation is a real data type for a number that has a fixed number of digits after the radix point . Fixed-point number representation can be compared to the more complicated floating point number representation....
     and floating-point, real-valued and complex-valued, multiplication and addition. Other typical operations supported by the hardware are circular buffer
    Circular buffer

    A circular buffer or ring buffer is a data structure that uses a single, fixed-size buffer as if it were connected end-to-end.This structure lends itself easily to buffering data streams....
    s and look-up tables. Examples of algorithms are the Fast Fourier transform
    Fast Fourier transform

    A fast Fourier transform is an efficient algorithm to compute the discrete Fourier transform and its inverse. There are many distinct FFT algorithms involving a wide range of mathematics, from simple complex number to group theory and number theory; this article gives an overview of the available techniques and some of their general propert...
     (FFT), finite impulse response
    Finite impulse response

    A finite impulse response filter is a type of a digital filter. The impulse response, the filter's response to a Kronecker delta input, is 'finite' because it settles to zero in a finite number of sampling intervals....
     (FIR) filter, Infinite impulse response
    Infinite impulse response

    Infinite impulse response is a property of signal processing systems. Systems with that property are known as IIR systems or when dealing with electronic filter systems as IIR filters....
     (IIR) filter, Wiener filter
    Wiener filter

    In signal processing, the Wiener filter is a filter proposed by Norbert Wiener during the 1940s and published in 1949. Its purpose is to reduce the amount of noise present in a signal by comparison with an estimation of the desired noiseless signal....
     and Kalman filter
    Kalman filter

    The Kalman filter is an efficient recursive filter that estimates the state of a Linear system from a series of noise measurements. It is used in a wide range of engineering applications from radar to computer vision, and is an important topic in control theory and control systems engineering....
    .


Fields of signal processing

  • Statistical signal processing
    Statistical signal processing

    Statistical signal processing is an area of signal processing that treats signals as stochastic processes, dealing with their statistical properties ....
     — analyzing and extracting information from signals based on their statistical properties
  • Audio signal processing
    Audio signal processing

    Audio signal processing, sometimes referred to as audio processing, is the intentional alteration of sound Signal , or sound. As audio signals may be electronically represented in either digital or analog signal format, signal processing may occur in either domain....
     — for electrical signals representing sound, such as speech or music
  • Speech signal processing
    Speech signal processing

    Speech signal processing refers to the acquisition, manipulation, storage, transfer and output of human utterances by a computer. The main goals are the recognition, synthesis and compression of human speech:...
     — for processing and interpreting spoken words
  • Image processing
    Image processing

    In electrical engineering and computer science, image processing is any form of signal processing for which the input is an , such as photographs or video frame; the output of image processing can be either an image or a set of characteristics or parameters related to the image....
     — in digital cameras, computers, and various imaging systems
  • Video processing
    Video processing

    In electrical engineering and computer science, video processing is a particular case of signal processing, where the input and output Signal s are video file formats or video streams....
     — for interpreting moving pictures
  • Array processing
    Array processing

    Array processing is signal processing of the outputs of an array of sensors to:* Enhance the signal-to-interference-plus-noise ratio compared to that of a single sensor using conventional or adaptive beamforming....
     — for processing signals from arrays of sensors


History

According to Alan V. Oppenheim and Ronald W. Schafer, the principles of signal processing can be found in the classical numerical analysis
Numerical analysis

Numerical analysis is the study of algorithms for the problems of continuous mathematics .One of the earliest mathematical writings is the Babylonian tablet YBC 7289, which gives a sexagesimal numerical approximation of , the length of the diagonal in a unit square....
 techniques of the 17th century. They further state that the "digitalization" or digital refinement of these techniques can be found in the digital control system
Control system

A control system is a device or set of devices to manage, command, direct or regulate the behavior of other devices or systems.There are two common classes of control systems, with many variations and combinations: logic gate, and feedback or linear controls....
s of the 1940s and 1950s.

See also

  • Data acquisition
    Data acquisition

    Data acquisition is the sampling of the real world to generate data that can be manipulated by a computer. Sometimes abbreviated DAQ or DAS, data acquisition typically involves acquisition of signals and waveforms and processing the signals to obtain desired information....