Digital Signal Processing (DSP) is one of the fastest growing fields of technology and computer science in the world, with typically a growth rate in excess of 30%. The growth of the computer industry has affected every corner of daily life and everyone is aware of this effect. In today's western world almost everyone uses DSPs in their everyday life, but unlike users of PCs almost no one knows that they are using DSPs. Digital Signal Processors (DSPs) are special purpose microprocessors and they are used in every form of electronic product, from mobile phones and CD players to the automotive industry; medical imaging systems to the electronic battlefield and from dishwashers to satellites.

DSP is all about analysing and processing real-world or analogue signals - the kind that humans interact with, for example speech. These signals are converted to a format that the computers can understand (digital) and then they are processed. The following diagram shows graphically the typical component parts of a DSP system.

In order to process analog signals with digital computers, they must first be converted to digital using analog to digital converters. Similarly the digital signals must be converted back to analog for them to be used outside the computer. The following diagram shows this process.

The diagram shows the representation of a real-world analog signal in blue and the digital representation of it in red. You will notice that the red line only matches the blue line at discrete points and these are called the sampling points. It is very important to take enough samples of the input so that it can be faithfully represented. The number of samples taken in one second is referred to as the sampling rate and a good rule-of-thumb is "the higher the sampling rate, the higher the cost of the system".

There are many reasons why we process these analog signals in the digital world (or domain) but these can all be reduced to two primary reasons, which are :

Cost - DSP systems are almost always cheaper than analog.
Functionality - DSP systems can perform many operations that are impossible in the analog world.

MPEG (pronounced M-peg), which stands for Moving Picture Experts Group, is the name of family of standards used for coding audio-visual information (e.g., movies, video, music) in a digital compressed format.

The major advantage of MPEG compared to other video and audio coding formats is that MPEG files are much smaller for the same quality. This is because MPEG uses very sophisticated compression techniques.

The figure shows each possible pair of data bits is represented by a different phase angle and figure 2 shows and example of a QPSK waveform. Because of QPSK, data rates are quoted in Symbol Rate rather than bit rate. In the case of QPSK modulation, the bit rate is twice high as the symbol rate. For example an SR of 20MS/s (20 mega-symbols) means 40Mb/s (40 mega-bits per second).

Voice Over Internet