Al-Hazmi de Nawaf

The treatment of the signal is the discipline which develops and studies the Technique S of treatment (Filtering, Amplification…), of analysis and Interpretation of the Signals. It thus calls largely upon the results of the Information theory, of the Statistique S like with many other fields of the Mathématiques applied.

General information

The signals to be treated can come from very diverse sources, but the majority are signals electric S or become electric using sensors and Transducteur S (microphones, retinas, sensors thermal, optical, of pressure, position, speed, acceleration and in general of all the physical and chemical sizes).

One distinguishes primarily the signals Analogique S which are produced by various Capteur S, Amplificateur S, converters digital-analog; the signals Numerical S resulting from Computer S, final, the reading of a numerical support or a Digitalization by an analog-to-digital converter.

The treatment can be made, without digitizing the signals, by analogical electronic circuits or also of the optical systems (treatment of the optical signal). It is more and more often carried out by Digital processing of the signal, using computers, of Microprocesseur S Embarqué S, of named specialized microprocessors DSP, of reconfigurable circuits (FPGA) or of numerical components dedicated (ASIC). There exist several particular branches of the treatment of the signal, according to the nature of the signals considered. In particular:

• Speech processing (or more generally sound) - for the analysis, the compression and the voice recognition
• Image processing S - for the analysis, the restoration and the compression of still images
• Treatment of the video - for the analysis and the compression of video sequences

The treatment of the signal can have various finalities:

• the detection of a signal
• the estimate of sizes to measure on a signal
• coding, the compression of the signal for its storage and its transmission
• improvement of its quality (restoration) according to physiological criteria (for listening and visualization).

The treatment of a signal carried out depends on the objectives. In particular, the concepts of signal and noise are subjective, they depend on what interests the user. One uses various measurements representative of the quality of a signal and information contained:

• the Rapport signal on noise, concept used very frequently but ambiguity since all depends on what is regarded signal and as noise.
• the number of effective bits Effective Number off Bits (ENOB) which is a measurement of the quality of analog-to-digital conversion.
• the Information of Fisher, useful in particular in estimate of parameters. It is the relative information with parameter or couple of parameters (matrix of information of Fisher).
• the Entropy, size resulting from the Physical statistics and the Information theory (work of Shannon), used in the operations of coding. It is a measurement of the “intrinsic” information of the signal.

Applications

Because they apply to all the stages of a chain of acquisition, analysis, transfer and restitution of the data, the techniques of the treatment of the signal find applications in practically all the fields of technology:

• in the telecommunications : that it is in the field of telephony or the terrestrial transfer of information numerical or via satellite, the compression of the data is paramount to exploit as well as possible the Band-width available, and to minimize the losses. The suppression of echoes is another scope of application.

• in audio : one seeks to improve the techniques of recording and compression to obtain greatest possible sound quality. The techniques of correction of echo make it possible to reduce the effects of reflections Acoustique S in the part. The treatment of the sound largely improved thanks to the computers. However, certain musicians speak more about a sound of nature different that from a simple qualitative improvement (just as CD " sonne" not like the Vinyl, and that certain groups, for example Genesis, particularly benefitted from the " new son" offered by the new support). The sound Synthèse makes it possible moreover to create artificial sounds or to recreate the sounds of natural instruments. It was in the beginning many upheavals in music.
• the analysis of the echoes makes it possible to obtain information on the medium on which the waves were reflected. This technique is exploited in the field of the imagery Radar or Sonar. In Geophysical , by analyzing the acoustic reflections of waves, one can determine the thickness and the nature of the layers of the basement. This technique is used in the field of the prospection for minerals and the prediction of the earthquakes.
• in imagery : one finds applications in the medical field (tomographic rebuilding, Imagerie by magnetic resonance - IRM), in the space (satellite treatment of photographs or images Radar). This field includes also the techniques of Pattern recognition and compression.
• the treatment of sequences video relates to compression, the restoration, the realization of special effects, and the extraction of descriptors (pattern recognition and textures, followed movements, characterization etc) in order to produce automatic annotations from the point of view of databases (research by the contents).

See too

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