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In information theory, a signal is the sequence of states of a communications channel that encodes a message. In a communications system, a transmitter encodes a message into a signal, which is carried to a receiver by the communications channel. For example, the words "Mary had a little lamb" might be the message spoken into a telephone. The telephone transmitter converts the sounds into an electrical voltage signal. The signal is transmitted to the receiving telephone by wires; and at the receiver it is reconverted into sounds. Information theory is the mathematical theory of data communication and storage, generally considered to have been founded in 1948 by Claude E. Shannon. ...
Mary had a little lamb is a popular nursery rhyme. ...
The volt (symbol: V) is the SI derived unit of electric potential difference. ...
Information theory studies both continuous signals, commonly called analog signals; and discrete signals (Shannon 2005, 3), or quantized signals, of which the most common today are digital signals . The information carried by a signal may be measured either on a per second basis, or per transmitted symbol; that is, either in continuous or discrete time (ibid, 19). An analog or analogue signal is any continuously variable signal. ...
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In information theory, the message is generated by a stochastic process, and the transmitted signal derives its statistical properties from the message. Conversely, usage of signal in reference to a process that generates a transmitted sequence of states in a communications channel implies that this process is stochastic. When it is not stochastic, misunderstandings can be created. Oldberg. (2005) reports that misunderstandings of this type plague the field of Defect Detection Testing. In the mathematics of probability, a stochastic process is a random function. ...
Analog and digital signals The two main types of signals are analog and digital. In short, the difference between them is that digital signals are discrete and quantized, as defined below, while analog signals possess neither property. An analog or analogue signal is any continuously variable signal. ...
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Discretization - Main article: Discrete signal
One of the fundamental distinctions between different types of signals is between continuous and discrete time. In the mathematical abstraction, the domain of a continuous-time (CT) signal is the set of real numbers (or some interval thereof), whereas the domain of a discrete-time signal is the set of integers (or some interval). What these integers represent depends on the nature of the signal. A discrete signal is a signal that has been sampled from a continuous signal. ...
Continuous time occurs when time is sampled continuously. ...
Discrete time is non-continuous time. ...
The integers consist of the positive natural numbers (1, 2, 3, …), their negatives (−1, −2, −3, ...) and the number zero. ...
DT signals often arise via of CT signals. For instance, sensors output data continuously, but since a continuous stream is impossible to record, a discrete signal is used as an approximation. Computers and other digital devices are restricted to discrete time. To meet Wikipedias quality standards, this article or section may require cleanup. ...
A computer is a machine for manipulating data according to a list of instructions - a program. ...
A digital system is one that uses numbers, especially binary numbers, for input, processing, transmission, storage, or display, rather than a continuous spectrum of values (an analog system) or non-numeric symbols such as letters or icons. ...
Quantization - Main article: Quantization (signal processing)
If a signal is to be represented as a sequence of numbers, it is impossible to maintain arbitrarily high precision - each number in the sequence must have a finite number of digits. As a result, the values of such a signal are restricted to belong to a finite set; in other words, it is quantized. Quantization of x using Q(x) = floor(Lx)/L. In digital signal processing, quantization is the process of approximating a continuous signal by a set of discrete symbols or integer values; that is, converting an analog signal to a digital one via analog-to-digital conversion. ...
In mathematics, a set is called finite if and only if there is a bijection between the set and some set of the form {1, 2, ..., n} where is a natural number. ...
Quantization of x using Q(x) = floor(Lx)/L. In digital signal processing, quantization is the process of approximating a continuous signal by a set of discrete symbols or integer values; that is, converting an analog signal to a digital one via analog-to-digital conversion. ...
Examples of signals - Motion. One can conceive of a signal representing the motion of a particle - say, a mote of dust, through some suitable space. The domain of a motion signal is one-dimensional (time), and the range is generally three-dimensional.
- Sound. Since a sound is a vibration of a medium (such as air), a sound signal associates a pressure value to every value of time. In the real world, sound signals are analog.
- Compact discs (CDs). CDs contain discrete signals representing sound, recorded at 44,100 samples per second. Each sample contains data for a left and right channel (since CDs are recorded in stereo).
- Pictures. A picture assigns a color value to each of a set of points. Since the points lie on a plane, the domain is two-dimensional. If the picture is a physical object, such as a painting, it's a continuous signal. If the picture a digital image, it's a discrete signal. It's often convenient to represent color as the sum of the intensities of three primary colors, so that the signal is vector-valued with dimension three.
- Videos. A video is a series of images. A point in a video is identified by its position (two-dimensional) and by the time at which it occurs, so a video signal has a three-dimensional domain.
In physics, motion means a change in the position of a body with respect to time, as measured by a particular observer in a particular frame of reference. ...
After just three years of use dust has blocked this laptop heat sink, making the computer unusable Dust is a general name for minute solid particles with diameter less than 500 micrometers (otherwise see sand or granulates) and, more generally, for finely divided matter. ...
Space is Big. ...
A schematic representation of hearing. ...
See Oscillator (disambiguation) for particular types of oscillation and oscillators. ...
Pressure(symbol: p) is the forceper unit areaacting on a surface in a direction perpendicularto that surface. ...
Interference colors. ...
Look up second in Wiktionary, the free dictionary. ...
Symbol for stereo Stereophonic sound, commonly called stereo, is the reproduction of sound, using two independent audio channels, through a pair of widely separated speaker systems, in such a way as to create a pleasant and natural impression of sound heard from various directions as in natural hearing. ...
For images in Wikipedia, see Wikipedia:Images. ...
A digital image is a representation of a two-dimensional image as a finite set of digital values, called picture elements or pixels. ...
Primary Colors, a 1996 novel by Anonymous (later revealed by Donald Foster to be journalist Joe Klein), is a roman à clef about U.S. President Bill Clintons first presidential campaign in 1992. ...
Look up Video in Wiktionary, the free dictionary Video is the technology of capturing, recording, processing, transmitting, and reconstructing moving pictures, typically using celluloid film, electronic signals, or digital media. ...
Membrane potential (or transmembrane potential or transmembrane potential difference or transmembrane potential gradient), is the electrical potential difference (voltage) across a cells plasma membrane. ...
It has been suggested that this article or section be merged with Electrophysiology. ...
Electric potential is the potential energy per unit charge associated with a static (time-invariant) electric field, also called the electrostatic potential, typically measured in volts. ...
Cells in culture, stained for keratin (red) and DNA (green). ...
Schematic of typical animal cell, showing subcellular components. ...
Drawing by Santiago Ramón y Cajal of cells in the pigeon cerebellum. ...
Electrophysiology is the study of the electrical properties of biological cells and tissues. ...
Frequency analysis - Main article: Frequency domain
It is remarkably useful to analyze the frequency spectrum of a signal. This technique is applicable to all signals, both continuous and discrete. For instance, if a signal is passed through an LTI system, the frequency spectrum of the resulting output signal is the product of the frequency spectrum of the original input signal and the frequency response of the system. Frequency domain is a term used to describe the analysis of mathematical functions with respect to frequency. ...
In mathematics, physics and signal processing, the frequency spectrum is a representation of a signal or other function in terms of frequency (in the frequency domain). It is the projection of the function onto a set of sinusoidal basis functions. ...
Linear time invarient systems are called as lti systems it should satisify both linearity and time invarient quality. ...
Frequency response is the measure of any systems response to frequency, but is usually used in connection with electronic amplifiers and similar systems, particularly in relation to audio signals. ...
Entropy Another important propery of a signal (actually, of a statistically defined class of signals) is its entropy or information content. Entropy of a Bernoulli trial as a function of success probability. ...
See also In science, and especially in physics and telecommunication, noise is fluctuations in and the addition of external factors to the stream of target information (signal) being received at a detector. ...
The phrase signal-to-noise ratio, often abbreviated SNR or S/N, is an engineering term for the ratio between the magnitude of a signal (meaningful information) and the magnitude of background noise. ...
Signal processing is the processing, amplification and interpretation of signals and deals with the analysis and manipulation of signals. ...
Digital signal processing (DSP) is the study of signals in a digital representation and the processing methods of these signals. ...
This article needs to be cleaned up to conform to a higher standard of quality. ...
Digital image processing is the use of computer algorithms to perform image processing on digital images. ...
Works cited Oldberg, T., 2005, "An Ethical Problem in the Statistics of Defect Detection Test Reliability," ndt.net, http://www.ndt.net/article/v10n05/oldberg/oldberg.htm .
Shannon, C. E., 2005 [1948], "A Mathematical Theory of Communication," (corrected reprint), accessed Dec. 15, 2005. Orig. 1948, Bell System Technical Journal, vol. 27, pp. 379-423, 623-656.
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