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. Performing numerical calculations does the processing of a digital signal.
Digital Signal Processing is a technique that converts signals from real world sources (usually in analog form) into digital data that can then be analyzed. Analysis is performed in digital form because once a signal has been reduced to numbers, its components can be isolated, analyzed and rearranged more easily than in analog form. Eventually, when the DSP has finished its work, the digital data can be turned back into an analog signal, with improved quality. For example, a DSP can filter noise from a signal, remove interference, amplify frequencies and suppress others, encrypt information, or analyze a complex wave form into its spectral components. This process must be handled in real-time - which is often very quickly. For instance, stereo equipment handles sound signals of up to 20 kilohertz (20,000 cycles per second), requiring a DSP to perform hundreds of millions of operations per second. Digital Signal Processor (DSP) is the heart of digital signal processing system.
Digital Signal Processor
A Digital Signal Processor is a special-purpose CPU (Central Processing Unit) that provides ultra-fast instruction sequences, such as shift and add, and multiply and add, which are commonly used in math-intensive signal processing applications. DSPs are not the same as typical microprocessors though. Microprocessors are typically general-purpose devices that run large blocks of software. They are not often called upon for real-time computation and they work at a slower pace, choosing a course of action, then waiting to finish the present job before responding to the next user command. A DSP, on the other hand, is often used as a type of embedded controller or processor that is built into another piece of equipment and is dedicated to a single group of tasks. In this environment, the DSP assists the general purpose host microprocessor.
Types of DSPs
Because different applications have varying ranges of frequencies, different DSPs are required. Their dynamic range, the spread of numbers that must be processed in the course of an application, classifies dSPs. This number is a function of the processors data width (the number of bits it manipulates) and the type of arithmetic it performs (fixed or floating point). For example, a 32-bit processor has a wider dynamic range than a 24-bit processor, which has a wider range than 16-bit processor. Floating-point chips have wider ranges than fixed-point devices. Each type of processor is suited for a particular range of applications. Sixteen-bit fixed-point DSPs are used for voice-grade systems such as phones, since they work with a relatively narrow range of sound frequencies. Hi-fidelity stereo sound has a wider range, calling for a 16-bit ADC (Analog/Digital Converter), and a 24-bit fixed point DSP. Image processing, 3-D graphics and scientific simulations have a much wider dynamic range and require a 32-bit floating-point processor.
DSP chips are used in sound cards, fax machines, modems, cellular phones, high-capacity hard disks and digital TVs. According to Texas Instruments, DSPs are used as the engine in 70% of the worlds digital cellular phones, and with the increase in wireless applications, this number will only increase.Digital signal processing is used in many fields including biomedicine, sonar, radar, seismology, speech and music processing, imaging and communications.
According to Forward Concepts, the market for DSP chips is growing at twice the rate of the semiconductor industry as a whole. They predict that over the next few years the digital signal processing business will increase by 33% annually, leading to an overall market of $11 billion in 1999. About $4.5 billion of this will be for general purpose DSPs.