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DSP
- Digital Signal Processor (Procesador digital de
señal). Es una unidad de
procesamiento, con arquitectura tipo PC, optimizada para
realizar operaciones de 24 o 32 bits en coma flotante en señales
discretas de audio digital. Esto permite realizar Transformadas
rápidas de Fourer (FFT), un algoritmo para calcular la
Transformada de Fourier Discreta (DFT), que convierte del
dominio del tiempo al de la frecuencia y puede analizar realizar
y otro tipo de operaciones complejas, en tiempo real, ajustar
repuesta de frecuencia, generar reverberación y otros efectos, y
separar ciertas bandas de frecuencias en canales separados.
Hacer este procesamiento de manera digital resulta más sencillo
y económico que hacerlo de manera analógica.
Prácticamente todos los receptores
de Cine en Casa actuales incorporan DSPs para generar sonido
multicanal envolvente desde fuentes estéreo.
What is DSP?
DSP, or Digital Signal Processing, as the term suggests, is the
processing of signals by digital means. A signal in this context
can mean a number of different things. Historically the origins
of signal processing are in electrical engineering, and a signal
here means an electrical signal carried by a wire or telephone
line, or perhaps by a radio wave. More generally, however, a
signal is a stream of information representing anything from
stock prices to data from a remote-sensing satellite. The term
"digital" comes from "digit", meaning a number (you count with
your fingers - your digits), so "digital" literally means
numerical; the French word for digital is numerique. A digital
signal consists of a stream of numbers, usually (but not
necessarily) in binary form. The processing of a digital signal
is done by performing numerical calculations.
Analog and digital signals
In many cases, the signal of interest is initially in the form
of an analog electrical voltage or current, produced for example
by a microphone or some other type of transducer. In some
situations, such as the output from the readout system of a CD
(compact disc) player, the data is already in digital form. An
analog signal must be converted into digital form before DSP
techniques can be applied. An analog electrical voltage signal,
for example, can be digitised using an electronic circuit called
an analog-to-digital converter or ADC. This generates a digital
output as a stream of binary numbers whose values represent the
electrical voltage input to the device at each sampling instant.
Signal processing
Signals commonly need to be processed in a variety of ways. For
example, the output signal from a transducer may well be
contaminated with unwanted electrical "noise". The electrodes
attached to a patient's chest when an ECG is taken measure tiny
electrical voltage changes due to the activity of the heart and
other muscles. The signal is often strongly affected by "mains
pickup" due to electrical interference from the mains supply.
Processing the signal using a filter circuit can remove or at
least reduce the unwanted part of the signal. Increasingly
nowadays, the filtering of signals to improve signal quality or
to extract important information is done by DSP techniques
rather than by analog electronics.
Development of DSP
The development of digital signal processing dates from the
1960's with the use of mainframe digital computers for number-crunching
applications such as the Fast Fourier Transform (FFT), which
allows the frequency spectrum of a signal to be computed rapidly.
These techniques were not widely used at that time, because
suitable computing equipment was generally available only in
universities and other scientific research institutions.
Digital Signal Processors (DSPs)
The introduction of the microprocessor in the late 1970's and
early 1980's made it possible for DSP techniques to be used in a
much wider range of applications. However, general-purpose
microprocessors such as the Intel x86 family are not ideally
suited to the numerically-intensive requirements of DSP, and
during the 1980's the increasing importance of DSP led several
major electronics manufacturers (such as Texas Instruments,
Analog Devices and Motorola) to develop Digital Signal Processor
chips - specialised microprocessors with architectures designed
specifically for the types of operations required in digital
signal processing. (Note that the acronym DSP can variously mean
Digital Signal Processing, the term used for a wide range of
techniques for processing signals digitally, or Digital Signal
Processor, a specialised type of microprocessor chip). Like a
general-purpose microprocessor, a DSP is a programmable device,
with its own native instruction code. DSP chips are capable of
carrying out millions of floating point operations per second,
and like their better-known general-purpose cousins, faster and
more powerful versions are continually being introduced. DSPs
can also be embedded within complex "system-on-chip" devices,
often containing both analog and digital circuitry.
Applications of DSP
DSP technology is nowadays commonplace in such devices as mobile
phones, multimedia computers, video recorders, CD players, hard
disc drive controllers and modems, and will soon replace analog
circuitry in TV sets and telephones. An important application of
DSP is in signal compression and decompression. Signal
compression is used in digital cellular phones to allow a
greater number of calls to be handled simultaneously within each
local "cell". DSP signal compression technology allows people
not only to talk to one another but also to see one another on
their computer screens, using small video cameras mounted on the
computer monitors, with only a conventional telephone line
linking them together. In audio CD systems, DSP technology is
used to perform complex error detection and correction on the
raw data as it is read from the CD.
Although some of the mathematical theory underlying DSP
techniques, such as Fourier and Hilbert Transforms, digital
filter design and signal compression, can be fairly complex, the
numerical operations required actually to implement these
techniques are very simple, consisting mainly of operations that
could be done on a cheap four-function calculator. The
architecture of a DSP chip is designed to carry out such
operations incredibly fast, processing hundreds of millions of
samples every second, to provide real-time performance: that is,
the ability to process a signal "live" as it is sampled and then
output the processed signal, for example to a loudspeaker or
video display. All of the practical examples of DSP applications
mentioned earlier, such as hard disc drives and mobile phones,
demand real-time operation.
The major electronics manufacturers have invested heavily in DSP
technology. Because they now find application in mass-market
products, DSP chips account for a substantial proportion of the
world market for electronic devices. Sales amount to billions of
dollars annually, and seem likely to continue to increase
rapidly.
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