Digital Signal Processing Reference
In-Depth Information
CHAPTER
1
An Overview of DSP
1.1 SIGNALS, WAVES, AND DIGITAL PROCESSING
Two of the human senses, sight and hearing, work via the detection of waves. Useful information from
both light and sound is gained by detection of certain characteristics of these waves, such as frequency and
amplitude. Modern telecommunication depends on transducing sound or light into electrical quantities
such as voltage, and then processing the voltage in many different ways to enable the information to
be reliably stored or conveyed to a distant place and then regenerated to imitate (i.e., reconstruct) the
original sound or light phenomenon.
For example, in the case of sound, a microphone detects rapid pressure variations in air and converts
those variations to an output voltage which varies in a manner proportional to the variation of pressure
on the microphone's diaphragm. The varying voltage can be used to cut a corresponding wave into a
wax disc, to record corresponding wave-like variations in magnetism onto a ferromagnetic wire or tape,
to vary the opacity of a linear track along the edge of a celluloid film (i.e., the sound-track of a motion
picture film) or perhaps to modulate a carrier wave for radio transmission.
In recent decades, signal processing and storage systems have been developed that use discrete
samples of a signal rather than the entire continuous time domain (or
analog
) signal. Several useful
definitions are as follows:
•A
sample
is the amplitude of an analog signal at an instant in time.
• A system that processes a signal in sampled form (i.e., a sequence of samples) is known as a
Discrete
Time Signal Processing System
.
•Ina
Digital Signal Processing
system, the samples are converted to numerical values, and the
values (numbers) stored (usually in binary form), transmitted, or otherwise processed.
The difference between conventional analog systems and digital systems is illustrated in Fig. 1.1.
At (a), a conventional analog system is shown, in which the signal from a microphone is sent directly to
an analog recording device, such as a tape recorder, recorded at a certain tape speed, and then played back
at the same speed some time later to reproduce the original sound. At (b), samples of the microphone
signal are obtained by an
Analog-to-Digital Converter (ADC)
, which converts instantaneous voltages
of the microphone signal to corresponding numerical values, which are stored in a digital memory, and
can later be sent to a
Digital-to-Analog Converter (DAC)
to reconstruct the original sound.
In addition to recording and reproducing analog signals, most other kinds of processing which
might be performed on an analog signal can also be performed on a sampled version of the signal by
using numerical algorithms. These can be categorized into two broad types of processing, time domain
and frequency domain, which are discussed in more detail below.
1.2 ADVANTAGES OF DIGITAL PROCESSING
The reduction of continuous signals to sequences of numerical values (samples) that can be used to
process and/or reconstruct the original signal, provides a number of benefits that cannot be achieved with
continuous or analog signal processing. The following are some of the benefits of digital processing:
