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Digital signal processing (
'DSP') is the study of
Signal (information theory)s in a digital representation and the processing methods of these signals. DSP and analog signal processing are subfields of
signal processing. DSP includes subfields like:
audio signal processing and speech signal processing, sonar and radar signal processing, sensor array processing, spectral estimation, statistical signal processing,
image processing, signal processing for communications, biomedical signal processing, etc.
Since the goal of DSP is usually to measure or filter continuous real-world analog signals, the first step is usually to convert the signal from an analog to a digital form, by using an
analog to digital converter. Often, the required output signal is another analog output signal, which requires a digital to analog converter.
The
algorithms required for DSP are sometimes performed using specialized computer hardware, which make use of specialized microprocessors called digital signal processors (also abbreviated
DSP). These process signals in real time and are generally purpose-designed
application-specific integrated circuits (ASICs). When flexibility and rapid development are more important than unit costs at high volume, DSP algorithms may also be implemented using field-programmable gate arrays (FPGAs).
DSP domains
In DSP, engineers usually study digital signals in one of the following domains: time domain (one-dimensional signals), spatial domain (multidimensional signals), frequency domain, autocorrelation domain, and
wavelet domains. They choose the domain in which to process a signal by making an informed guess (or by trying different possibilities) as to which domain best represents the essential characteristics of the signal. A sequence of samples from a measuring device produces a time or spatial domain representation, whereas a
discrete Fourier transform produces the frequency domain information, that is the
frequency spectrum. Autocorrelation is defined as the
cross-correlation of the signal with itself over varying intervals of time or space.
Signal sampling
With the increasing use of
computers the usage and need of digital signal processing has increased. In order to use an analog signal on a computer it must be digitized with an
analog to digital converter (
ADC).Sampling is usually carried out in two stages,
discretization and
Quantization (signal processing). In the discretization stage, the space of signals is partitioned into
equivalence classes and discretization is carried out by replacing the signal with representative signal of the corresponding equivalence class.In the quantization stage the representative signal values are approximated by values from a finite set.
In order for a sampled analog signal to be exactly reconstructed, the Nyquist-Shannon sampling theorem must be satisfied. This theorem states that the sampling frequency must be greater than twice the bandwidth of the signal. In practice, the sampling frequency is often significantly more than twice the required bandwidth. The most common bandwidth scenarios are: DC - BWx (baseband); and Fc +/-BWx, a frequency band centered on a carrier frequency ("direct demodulation").
A digital to analog converter (DAC) is used to convert the digital signal back to analog. The use of a digital computer is a key ingredient into
digital control.
Time and space domains
The most common processing approach in the time or space domain is enhancement of the input signal through a method called filtering. Filtering generally consists of some transformation of a number of surrounding samples around the current sample of the input or output signal. There are various ways to characterize filters; for example:
- A "linear" filter is a linear transformation of input samples; other filters are "non-linear." Linear filters satisfy the superposition condition, i.e. if an input is a weighted linear combination of different signals, the output is an equally weighted linear combination of the corresponding output signals.
- A "causal" filter uses only previous samples of the input or output signals; while a "non-causal" filter uses future input samples. A non-causal filter can usually be changed into a causal filter by adding a delay to it.
- A "time-invariant" filter has constant properties over time; other filters such as adaptive filters change in time.
- Some filters are "stable", others are "unstable". A stable filter produces an output that converges to a constant value with time, or remains bounded within a finite interval. An unstable filter produces output which diverges.
- A "finite impulse response" (Finite impulse response) filter uses only the input signal, while an "infinite impulse response" filter (IIR) uses both the input signal and previous samples of the output signal. FIR filters are always stable, while IIR filters may be unstable.
Most filters can be described in Z-domain (a superset of the frequency domain) by their
transfer functions. A filter may also be described as a difference equation, a collection of Zero (complex analysis) and
pole (complex analysis)s or, if it is an FIR filter, an
impulse response or step response. The output of an FIR filter to any given input may be calculated by
convolution the input signal with the impulse response. Filters can also be represented by block diagrams which can then be used to derive a sample processing
algorithm to implement the filter using hardware instructions.
Frequency domain
Signals are converted from time or space domain to the frequency domain usually through the Fourier transform. The Fourier transform converts the signal information to a magnitude and phase component of each frequency. Often the Fourier transform is converted to the power spectrum, which is the magnitude of each frequency component squared.
The most common purpose for analysis of signals in the frequency domain is analysis of signal properties. The engineer can study the spectrum to get information of which frequencies are present in the input signal and which are missing.
There are some commonly used frequency domain transformations. For example, the cepstrum converts a signal to the frequency domain through Fourier transform, takes the logarithm, then applies another Fourier transform. This emphasizes the frequency components with smaller magnitude while retaining the order of magnitudes of frequency components.
Applications
The main applications of DSP are
audio signal processing, audio compression, digital image processing,
video compression,
speech processing,
speech recognition, digital communications,
RADAR, SONAR, seismology, and biomedicine. Specific examples are
speech compression and transmission in digital
mobile phones, room matching equalization of sound in
Hifi and sound reinforcement applications, weather forecasting, economic forecasting,
seismology data processing, analysis and control of industrial processes, computer-generated
animations in Films,
medical imaging such as CAT scans and MRI,
computer graphics, high fidelity loudspeaker crossovers and equalization, and
sound effect for use with electric guitar
amplifiers.
Implementation
Digital signal processing is often implemented using
Digital signal processor such as the MC56000 and the TMS320. These often process data using fixed-point arithmetic, although some versions are available which use
floating point arithmetic and are more powerful. For faster applications
FPGAs might be used. Beginning in 2007, multicore implementations of DSPs have started to emerge from companies including Freescale and startup Stream Processors, Inc. For faster applications with vast usage,
ASICs might be designed specifically. For slow applications such as flame scanning, a traditional slower processor such as a microcontroller can cope.
Techniques
Related fields
References
- Alan V Oppenheim, Ronald W Schafer, John R. Buck : Discrete-Time Signal Processing, Prentice Hall, ISBN 0-13-754920-2
- Boaz Porat: A Course in Digital Signal Processing, Wiley, ISBN 0471149616
- Richard G. Lyons: Understanding Digital Signal Processing, Prentice Hall, ISBN 0-13-108989-7
- Jonathan (Y) Stein, Digital Signal Processing, a Computer Science Perspective, Wiley, ISBN 0-471-29546-9
- Sen M. Kuo, Woon-Seng Gan: Digital Signal Processors: Architectures, Implementations, and Applications, Prentice Hall, ISBN 0-13-035214-4
- Bernard Mulgrew, Peter Grant, John Thompson: Digital Signal Processing - Concepts and Applications, Palgrave Macmillan, ISBN 0-333-96356-3
- Steven W. Smith: Digital Signal Processing - A Practical Guide for Engineers and Scientists, Newnes, ISBN 0-7506-7444-X
- Paul A. Lynn, Wolfgang Fuerst: Introductory Digital Signal Processing with Computer Applications, John Wiley & Sons, ISBN 0-471-97984-8
- James D. Broesch: Digital Signal Processing Demystified, Newnes, ISBN 1-878707-16-7
- John G. Proakis, Dimitris Manolakis: Digital Signal Processing - Principles, Algorithms and Applications, Pearson, ISBN 0-13-394289-9
- Hari Krishna Garg: Digital Signal Processing Algorithms, CRC Press, ISBN 0-8493-7178-3
- P. Gaydecki: Foundations Of Digital Signal Processing: Theory, Algorithms And Hardware Design, Institution of Electrical Engineers, ISBN 0-85296-431-5
- Paul M. Embree, Damon Danieli: C++ Algorithms for Digital Signal Processing, Prentice Hall, ISBN 0-13-179144-3
- Anthony Zaknich: Neural Networks for Intelligent Signal Processing, World Scientific Pub Co Inc, ISBN 981-238-305-0
- Vijay Madisetti, Douglas B. Williams: The Digital Signal Processing Handbook, CRC Press, ISBN 0-8493-8572-5
- Stergios Stergiopoulos: Advanced Signal Processing Handbook: Theory and Implementation for Radar, Sonar, and Medical Imaging Real-Time Systems, CRC Press, ISBN 0-8493-3691-0
- Joyce Van De Vegte: Fundamentals of Digital Signal Processing, Prentice Hall, ISBN 0-13-016077-6
- Ashfaq Khan: Digital Signal Processing Fundamentals, Charles River Media, ISBN 1-58450-281-9
- Jonathan M. Blackledge, Martin Turner: Digital Signal Processing: Mathematical and Computational Methods, Software Development and Applications, Horwood Publishing, ISBN 1-898563-48-9
- Bimal Krishna, K. Y. Lin, Hari C. Krishna: Computational Number Theory & Digital Signal Processing, CRC Press, ISBN 0-8493-7177-5
- Doug Smith: Digital Signal Processing Technology: Essentials of the Communications Revolution, American Radio Relay League, ISBN 0-87259-819-5
- Henrique S. Malvar: Signal Processing with Lapped Transforms, Artech House Publishers, ISBN 0-89006-467-9
- Charles A. Schuler: Digital Signal Processing: A Hands-On Approach, McGraw-Hill, ISBN 0-07-829744-3
- James H. McClellan, Ronald W Schafer, Mark A. Yoder: Signal Processing First, Prentice Hall, ISBN 0-13-090999-8
- Artur Krukowski, Izzet Kale: DSP System Design: Complexity Reduced Iir Filter Implementation for Practical Applications, Kluwer Academic Publishers, ISBN 1-4020-7558-8
- John G. Proakis: A Self-Study Guide for Digital Signal Processing, Prentice Hall, ISBN 0-13-143239-7
External links
- DSPwiki.com A Wiki dedicated to DSP and Synthesis.
- DSP Processor Core-Based Wireless System Design Conventional/VLIW DSPs and processor architectures.
- Signal processing libraries from Intel(R) Integrated Performance Primitives
- Introduction to Signal Processing (pdf) Brief 8-page introduction
- DSP - Digital signal processing
- 2007 IDC Report on On-Demand Video Transcoding
Online books:
- The Scientist and Engineer's Guide to Digital Signal Processing, a book on DSP with all content available online, by Steven W. Smith, Ph.D.
- wikibooks:Digital Signal Processing
Digital Signal Processing Tutorial
An outline of the basic principles of DSP (Digital Signal Processing), including tutorials and Java applets illustrating DSP techniques
Digital Signal Processing from FOLDOC
Digital Signal Processing (DSP) Computer manipulation of analog signals (commonly sound or image) which have been converted to digital form (sampled).
Digital Signal Processing Language from FOLDOC
Digital Signal Processing Language < language > (DSPL) A C-derived DSP language. ["The Programming Language DSPL", A. Schwarte & H. Hanselmann, Proc PCIM 90, 1990].
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