The MPEG-2 system compresses the analogue signal into chunks of digital data that is transmitted and received by a suitable decoder. Only the changes from one picture frame to the next are sent, thus reducing the amount of data that needs to be sent in order to reconstruct the original picture. The picture you see is constantly being updated, or 'refreshed', as more data is received. The picture is not completely replaced with a new one -
Digital data is recorded as individual 'bits', with each bit representing either an 'on' or 'off' instruction. The more bits sent during any given time period means more information is received which results in a better quality picture. Every item of digital hardware transfers digital bits at a certain 'bitrate'. This is where digital television experiences its first problem. Under normal conditions, the bitrate of digital TV is enough to ensure that all the required information across every channel gets through clearly. But when the bitrate is too slow to get the needed information to the receiver, like when several channels are showing fast, action sequences, the amount of information available to each channel is reduced.
DIGITAL TV SOUND
The standard sound format for European digital television comes in the form of MPEG-2 Stereo. This system can carry two channels of CD quality digital audio, and can even carry additional channels interlaced with the stereo audio enabling the broadcast of Dolby Surround soundtracks for playback on Dolby Pro-Logic hardware. o