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Signal processing is an
electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the la ...

electrical engineering
subfield that focuses on analysing, modifying, and synthesizing
signal In signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal processing, sound, image processing, images, and scientific measurements. Sig ...

signal
s such as
sound In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. ...
,
images An Synthetic aperture radar, SAR radar imaging, radar image acquired by the SIR-C/X-SAR radar on board the Space Shuttle Endeavour shows the Teide volcano. The city of Santa Cruz de Tenerife is visible as the purple and white area on the lowe ...
, and scientific measurements. Signal processing techniques can be used to improve transmission, storage efficiency and subjective quality and to also emphasize or detect components of interest in a measured signal.


History

According to Alan V. Oppenheim and Ronald W. Schafer, the principles of signal processing can be found in the classical
numerical analysis (c. 1800–1600 BC) with annotations. The approximation of the square root of 2 is four sexagesimal figures, which is about six decimal figures. 1 + 24/60 + 51/602 + 10/603 = 1.41421296... Numerical analysis is the study of algorithms that use num ...
techniques of the 17th century. They further state that the digital refinement of these techniques can be found in the digital
control system A control system manages, commands, directs, or regulates the behavior of other devices or systems using control loop A control loop is the fundamental building block of industrial control systems. It consists of all the physical components an ...
s of the 1940s and 1950s. In 1948,
Claude Shannon Claude Elwood Shannon (April 30, 1916 – February 24, 2001) was an American mathematician A mathematician is someone who uses an extensive knowledge of mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such top ...
wrote the influential paper "
A Mathematical Theory of Communication "A Mathematical Theory of Communication" is an article by mathematician A mathematician is someone who uses an extensive knowledge of mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (numb ...
" which was published in the
Bell System Technical Journal The ''Bell Labs Technical Journal'' is the in-house scientific journal In academic publishing Academic publishing is the subfield of publishing Publishing is the activity of making information, literature, music, software and other conte ...
. The paper laid the groundwork for later development of information communication systems and the processing of signals for transmission. Signal processing matured and flourished in the 1960s and 1970s, and digital signal processing became widely used with specialized
digital signal processor The NeXTcube from 1990 had a Motorola 68040 (25 MHz) and a digital signal processor Motorola 56001">Motorola_68040.html" ;"title="NeXTcube from 1990 had a Motorola 68040">NeXTcube from 1990 had a Motorola 68040 (25 MHz) and a digital signal proce ...
chips in the 1980s.


Categories


Analog

Analog signal processing is for signals that have not been digitized, as in most 20th-century radio, telephone, radar, and television systems. This involves linear electronic circuits as well as nonlinear ones. The former are, for instance,
passive filter Passivity is a property of engineering systems, most commonly encountered in analog electronics Analogue electronics ( en-US, analog electronics) are electronic systems with a continuously variable signal, in contrast to digital electronics wh ...
s,
active filter An active filter is a type of analog circuit implementing an electronic filter using active components, typically an amplifier. Amplifiers included in a filter design can be used to improve the cost, performance and predictability of a filter. A ...
s, additive mixers,
integrator An integrator in measurement and control applications is an element whose output signal is the time integral In mathematics, an integral assigns numbers to functions in a way that describes displacement, area, volume, and other concepts that a ...

integrator
s, and delay lines. Nonlinear circuits include
compandor Image:Waveformcompanded.png, After compressing, before expanding In telecommunication and signal processing, companding (occasionally called compansion) is a method of mitigating the detrimental effects of a channel with limited dynamic range. Th ...
s, multipliers (
frequency mixer 350px, Frequency mixer symbol In electronics Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. It uses active devices to control electr ...

frequency mixer
s,
voltage-controlled amplifierA variable-gain or voltage-controlled amplifier is an electronic amplifier that varies its gain depending on a control voltage (often abbreviated CV). VCAs have many applications, including audio level compression, synthesizers and amplitude mo ...
s),
voltage-controlled filter A voltage-controlled filter (VCF) is an electronic filter whose operating characteristics (primarily cutoff frequency) can be set by an input control voltage. Voltage controlled filters are widely used in Synthesizer, synthesizers. A music synthe ...
s,
voltage-controlled oscillator image:General Microwave VCO.png, A microwave (12–18GHz) voltage-controlled oscillator A voltage-controlled oscillator (VCO) is an electronic oscillator whose oscillation frequency is controlled by a voltage input. The applied input voltage determ ...
s, and
phase-locked loop A phase-locked loop or phase lock loop (PLL) is a control system that generates an output Signal (electrical engineering), signal whose phase (waves), phase is related to the phase of an input signal. There are several different types; the simpl ...

phase-locked loop
s.


Continuous time

Continuous-time signal processing is for signals that vary with the change of continuous domain (without considering some individual interrupted points). The methods of signal processing include
time domain Time domain refers to the analysis of mathematical functions Mathematics (from Greek: ) includes the study of such topics as quantity Quantity is a property that can exist as a multitude or magnitude, which illustrate discontinuity a ...
,
frequency domain In physics, electronics, control systems engineering, and statistics, the frequency domain refers to the analysis of mathematical functions or Signal (information theory), signals with respect to frequency, rather than time. Put simply, a time-dom ...
, and complex frequency domain. This technology mainly discusses the modeling of linear time-invariant continuous system, integral of the system's zero-state response, setting up system function and the continuous time filtering of deterministic signals


Discrete time

Discrete-time signal processing is for sampled signals, 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 In electronics Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. It uses active devices to control electron flow by amplifier, amplif ...

sample and hold
circuits, analog time-division
multiplexer In electronics Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. It uses active devices to control electron flow by amplifier, amplif ...

multiplexer
s,
analog delay line File:Torsion_wire_delay_line.jpg, 250px, A magnetostrictive torsion wire delay line. An analog delay line is a Electrical network, network of electronic component, electrical components connected in cascade connection, cascade, where each indivi ...
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, in mathematics and digital signal processing#REDIRECT Digital signal processing {{Redirect category shell, 1= {{R from other capitalisation ..., is the process of mapping input values from a large set (often a continuous set) to ...

quantization error
into consideration.


Digital

Digital signal processing is the processing of digitized discrete-time sampled signals. Processing is done by general-purpose
computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known as Computer program, programs. These ...

computer
s or by digital circuits such as
ASIC An application-specific integrated circuit (ASIC ) is an integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuit 200px, A circuit b ...
s,
field-programmable gate array A field-programmable gate array (FPGA) is an integrated circuit designed to be configured by a customer or a designer after manufacturinghence the term ''Field-programmability, field-programmable''. The FPGA configuration is generally specifie ...
s or specialized
digital signal processor The NeXTcube from 1990 had a Motorola 68040 (25 MHz) and a digital signal processor Motorola 56001">Motorola_68040.html" ;"title="NeXTcube from 1990 had a Motorola 68040">NeXTcube from 1990 had a Motorola 68040 (25 MHz) and a digital signal proce ...
s (DSP chips). Typical arithmetical operations include fixed-point and
floating-point In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithm of an algorithm (Euclid's algorithm) for calculating the greatest com ...
, real-valued and complex-valued, multiplication and addition. Other typical operations supported by the hardware are
circular buffer In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of Algo ...

circular buffer
s and
lookup table In computer science, a lookup table (LUT) is an array data structure, array that replaces runtime (program lifecycle phase), runtime computation with a simpler array indexing operation. The process is termed as "direct addressing" and LUTs differ fr ...
s. Examples of algorithms are the
fast Fourier transform A fast Fourier transform (FFT) is an algorithm that computes the discrete Fourier transform (DFT) of a sequence, or its inverse (IDFT). Fourier analysis converts a signal from its original domain (often time or space) to a representation in t ...
(FFT),
finite impulse response In , a finite impulse response (FIR) filter is a whose (or response to any finite length input) is of ''finite'' duration, because it settles to zero in finite time. This is in contrast to (IIR) filters, which may have internal feedback and may ...
(FIR) filter,
Infinite impulse response Infinite may refer to: Mathematics * Infinite set, a set that is not a finite set * Infinity, an abstract concept describing something without any limit Music * Infinite (band), a South Korean boy band *''Infinite'' (EP), debut EP of American m ...
(IIR) filter, and
adaptive filter An adaptive filter is a system with a linear filter (signal processing), filter that has a transfer function controlled by variable parameters and a means to adjust those parameters according to an optimization algorithm. Because of the complexity ...
s such as the Wiener and
Kalman filter For statistics Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics to a scientific, industrial, or social problem, it is conventional to begin w ...
s.


Nonlinear

Nonlinear signal processing involves the analysis and processing of signals produced from nonlinear systems and can be in the time, frequency, or spatio-temporal domains. Nonlinear systems can produce highly complex behaviors including bifurcations,
chaos Chaos or CHAOS may refer to: Arts, entertainment and media Fictional elements * Chaos (Kinnikuman), Chaos (''Kinnikuman'') * Chaos (Sailor Moon), Chaos (''Sailor Moon'') * Chaos (Sesame Park), Chaos (''Sesame Park'') * Chaos (Warhammer), Chaos ('' ...
,
harmonics A harmonic is any member of the harmonic series Harmonic series may refer to either of two related concepts: *Harmonic series (mathematics) *Harmonic series (music) {{Disambig .... The term is employed in various disciplines, including music ...

harmonics
, and
subharmonics In music Music is the of arranging s in time through the of melody, harmony, rhythm, and timbre. It is one of the aspects of all human societies. General include common elements such as (which governs and ), (and its associated con ...
which cannot be produced or analyzed using linear methods. Polynomial signal processing is a type of non-linear signal processing, where
polynomial In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). I ...

polynomial
systems may be interpreted as conceptually straight forward extensions of linear systems to the non-linear case.


Statistical

Statistical signal processing is an approach which treats signals as
stochastic process In probability theory and related fields, a stochastic () or random process is a mathematical object usually defined as a Indexed family, family of random variables. Stochastic processes are widely used as mathematical models of systems and phen ...

stochastic process
es, utilizing their
statistical Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data Data are units of information Information can be thought of as the resolution of uncertainty; it answers th ...

statistical
properties to perform signal processing tasks. Statistical techniques are widely used in signal processing applications. For example, one can model the
probability distribution In probability theory Probability theory is the branch of mathematics concerned with probability. Although there are several different probability interpretations, probability theory treats the concept in a rigorous mathematical manner by expre ...
of noise incurred when photographing an image, and construct techniques based on this model to in the resulting image.


Application fields

*
Audio signal processing Audio signal processing is a subfield of that is concerned with the electronic manipulation of s. Audio signals are electronic representations of s—s which travel through air, consisting of compressions and rarefactions. The energy contained ...
for electrical signals representing sound, such as
speech Speech is human vocal communication Communication (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, ...
or music *
Image processing Digital image processing is the use of a digital computer A computer is a machine A machine is a man-made device that uses power to apply forces and control movement to perform an action. Machines can be driven by animals and people ...
in digital cameras, computers and various imaging systems *
Video processingIn electronics engineering, video processing is a particular case of signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal processing, sound ...
for interpreting moving pictures *
Wireless communication Wireless communication (or just wireless, when the context allows) is the transfer of information between two or more points that do not use an electrical conductor In physics Physics (from grc, φυσική (ἐπιστήμη), ph ...
waveform generations, demodulation, filtering, equalization *
Control systems A control system manages, commands, directs, or regulates the behavior of other devices or systems using s. It can range from a single home heating controller using a controlling a domestic boiler to large s which are used for controlling or ...
* Array processing for processing signals from arrays of sensors *
Process control An industrial process control in continuous production processes is a discipline that uses industrial control system#REDIRECT Industrial control system Industrial control system (ICS) is a general term that encompasses several types of control s ...
a variety of signals are used, including the industry standard 4-20 mA
current loop In electrical Signal (electrical engineering), signalling an analog current loop is used where a device must be monitored or controlled remotely over a pair of conductors. Only one current level can be present at any time. A major application of c ...
*
Seismology Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "Earthquake, earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of Linear elasticity#Elastic wave, elast ...
*
Financial signal processing Financial signal processing is a branch of signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal processing, sound, image processing, image ...
analyzing financial data using signal processing techniques, especially for prediction purposes. *
Feature extractionIn machine learning, pattern recognition, and image processing, feature extraction starts from an initial set of measured data and builds derived values (Feature (machine learning), features) intended to be informative and non-redundant, facilitatin ...
, such as image understanding and
speech recognition Speech recognition is an interdisciplinary subfield of computer science and computational linguistics that develops Methodology, methodologies and technologies that enable the recognition and translation of spoken language into text by computers ...

speech recognition
. * Quality improvement, such as
noise reduction Noise reduction is the process of removing noise from a signal In signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal processing, ...

noise reduction
,
image enhancement Image editing encompasses the processes of altering image An SAR radar imaging, radar image acquired by the SIR-C/X-SAR radar on board the Space Shuttle Endeavour shows the Teide volcano. The city of Santa Cruz de Tenerife is visible a ...
, and
echo cancellation Echo suppression and echo cancellation are methods used in telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunication Telecommunication is the transmission of information ...
. * Source coding including audio compression,
image compression Image compression is a type of data compression In signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal processing, sound, image proc ...
, and
video compression In signal processing, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either Lossy compression, lossy or Lossless comp ...
. *
Genomic Genomics is an interdisciplinary field of focusing on the structure, function, evolution, mapping, and editing of s. A genome is an organism's complete set of , including all of its genes as well as its hierarchical, three-dimensional structur ...
signal processing In communication systems, signal processing may occur at: * 1 in the seven layer OSI model, the
physical layer In the seven-layer OSI model The Open Systems Interconnection model (OSI model) is a that characterises and standardises the communication functions of a or computing system without regard to its underlying internal structure and technolo ...
(
modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informatio ...

modulation
, equalization,
multiplexing In telecommunications Telecommunication is the transmission of information by various types of technologies over wire, radio, Optical system, optical, or other Electromagnetism, electromagnetic systems. It has its origin in the desire of ...
, etc.); * OSI layer 2, the
data link layer The data link layer, or layer 2, is the second layer of the seven-layer OSI model The Open Systems Interconnection model (OSI model) is a that characterises and standardises the communication functions of a or computing system without r ...
(
forward error correction In computing, telecommunication, information theory, and coding theory, an error correction code, sometimes error correcting code, (ECC) is used for error control, controlling errors in data over unreliable or noisy communication channels. The cen ...
); * OSI layer 6, the
presentation layer In the seven-layer OSI model The Open Systems Interconnection model (OSI model) is a conceptual model A conceptual model is a representation of a system, made of the composition of concept Concepts are defined as abstract ideas or general ...
(source coding, including analog-to-digital conversion and
data compression In signal processing Signal processing is an electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electro ...
).


Typical devices

*
Filters Filter, filtering or filters may refer to: Science and technology Device * Filter (chemistry), a device which separates solids from fluids (liquids or gases) by adding a medium through which only the fluid can pass ** Filter (aquarium), critical ...
for example analog (passive or active) or digital (
FIR Firs (''Abies'') are a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology Biology is the natural science that studies life and living organisms, including ...

FIR
, , frequency domain or stochastic filters, etc.) * Samplers and
analog-to-digital converter In electronics, an analog-to-digital converter (ADC, A/D, or A-to-D) is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a Digital signal (signal processing), digit ...
s for signal acquisition and reconstruction, which involves measuring a physical signal, storing or transferring it as digital signal, and possibly later rebuilding the original signal or an approximation thereof. * Signal compressors *
Digital signal processor A digital signal processor (DSP) is a specialized microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit An integrated circuit or monolithic i ...
s (DSPs)


Mathematical methods applied

*
Differential equations In mathematics, a differential equation is an equation In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), ...
*
Recurrence relation In mathematics Mathematics (from Greek: ) includes the study of such topics as numbers ( and ), formulas and related structures (), shapes and spaces in which they are contained (), and quantities and their changes ( and ). There is no gener ...
* Transform theory * for processing non-stationary signals *
Spectral estimation In statistical signal processing, the goal of spectral density estimation (SDE) is to estimation theory, estimate the spectral density (also known as the power spectrum, power spectral density) of a random signal from a sequence of time samples of ...
for determining the spectral content (i.e., the distribution of power over frequency) of a time series *
Statistical signal processing Signal processing is an electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electronics, and electromagnetis ...
analyzing and extracting information from signals and noise based on their stochastic properties *
Linear time-invariant system In system analysis, among other fields of study, a linear time-invariant system (or "LTI system") is a system that produces an output signal from any input signal subject to the constraints of Linear system#Definition, linearity and Time-invariant ...
theory, and transform theory * Polynomial signal processing analysis of systems which relate input and output using polynomials *
System identification The field of system identification uses statistical methods to build mathematical model A mathematical model is a description of a system A system is a group of Interaction, interacting or interrelated elements that act according to a set o ...
and classification *
Calculus Calculus, originally called infinitesimal calculus or "the calculus of infinitesimals", is the mathematics, mathematical study of continuous change, in the same way that geometry is the study of shape and algebra is the study of generalizations ...

Calculus
*
Complex analysis Complex analysis, traditionally known as the theory of functions of a complex variable, is the branch of mathematical analysis Analysis is the branch of mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such ...
* Vector spaces and
Linear algebra Linear algebra is the branch of mathematics concerning linear equations such as: :a_1x_1+\cdots +a_nx_n=b, linear maps such as: :(x_1, \ldots, x_n) \mapsto a_1x_1+\cdots +a_nx_n, and their representations in vector spaces and through matrix (mat ...
*
Functional analysis 200px, One of the possible modes of vibration of an idealized circular drum head. These modes are eigenfunctions of a linear operator on a function space, a common construction in functional analysis. Functional analysis is a branch of mathemat ...
*
Probability Probability is the branch of mathematics Mathematics (from Greek: ) includes the study of such topics as numbers (arithmetic and number theory), formulas and related structures (algebra), shapes and spaces in which they are contained ...

Probability
and
stochastic processes In probability theory Probability theory is the branch of mathematics concerned with probability. Although there are several different probability interpretations, probability theory treats the concept in a rigorous mathematical manner by expre ...
*
Detection theory Detection theory or signal detection theory is a means to measure the ability to differentiate between information-bearing patterns (called stimulus A stimulus is something that causes a physiological response. It may refer to: *Stimulation Stim ...
*
Estimation theory Estimation theory is a branch of statistics Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics to a scientific, industrial, or social problem ...
*
Optimization File:Nelder-Mead Simionescu.gif, Nelder-Mead minimum search of Test functions for optimization, Simionescu's function. Simplex vertices are ordered by their values, with 1 having the lowest ( best) value., alt= Mathematical optimization (alter ...
*
Numerical methods (c. 1800–1600 BC) with annotations. The approximation of the square root of 2 is four sexagesimal Sexagesimal, also known as base 60 or sexagenary, is a numeral system with 60 (number), sixty as its radix, base. It originated with the ancient ...
*
Time series In mathematics Mathematics (from Greek: ) includes the study of such topics as numbers ( and ), formulas and related structures (), shapes and spaces in which they are contained (), and quantities and their changes ( and ). There is no gen ...

Time series
*
Data mining Data mining is a process of extracting and discovering patterns in large data set A data set (or dataset) is a collection of data Data (; ) are individual facts, statistics, or items of information, often numeric. In a more technical sens ...
for statistical analysis of relations between large quantities of variables (in this context representing many physical signals), to extract previously unknown interesting patterns


See also

*
Audio filter An audio filter is a frequency dependent amplifier circuit, working in the audio frequency An audio frequency or audible frequency (AF) is a periodic function, periodic vibration whose frequency is in the band audible to the average human, the ...
*
Bounded variation In mathematical analysis Analysis is the branch of mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calcu ...
*
Digital image processing Digital image processing is the use of a digital computer A computer is a machine A machine is a man-made device that uses power to apply forces and control movement to perform an action. Machines can be driven by animals and people ...
*
Dynamic range compression Dynamic range compression (DRC) or simply compression is an audio signal processing Audio signal processing is a subfield of signal processing that is concerned with the electronic manipulation of audio signals. Audio signals are electroni ...
,
companding After compressing, before expanding In telecommunication Telecommunication is the transmission of information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and thus defi ...
, limiting, and noise gating * Information theory * Non-local means * Reverberation


References


Further reading

* * * * Kainam Thomas Won

Statistical Signal Processing lecture notes at the University of Waterloo, Canada. * Ali H. Sayed, Adaptive Filters, Wiley, NJ, 2008, . * Thomas Kailath, Ali H. Sayed, and Babak Hassibi, Linear Estimation, Prentice-Hall, NJ, 2000, .


External links


Signal Processing for Communications
– free online textbook by Paolo Prandoni and Martin Vetterli (2008)
Scientists and Engineers Guide to Digital Signal Processing
– free online textbook by Stephen Smith {{Authority control Signal processing, Mass media technology Telecommunication theory