Remember the old days of analog TV, radio, etc. Most of us do unless you're really young. And still today there are plenty of analog systems in use. Normal radio still uses analog transmission. But the digital age has begun and more and more we will use digital systems rather than analog systems.
Digital transmission systems have many advantages over analog transmission systems, like higher quality of audio and video. How come digital systems can transmit higher quality signals than analog systems? The truth is that they don't. They just use some tricks to eliminate noise.
Analog Transmission Systems
When something like video and audio, is recorded by an analog system, the recording has a certain quality. This recording (when done professionally) has a very high quality. When the recording is transmitted it is modulated directly to a carrier wave, which is then transmitted through the air, cable, via satellite, etc. During this transmission, the carrier and the modulated signal will loose amplitude (power) and due to interference noise is introduced to the carrier and its modulated signal. The result will always be a received signal that has a lower quality than the transmitted signal. Hence, the modulated signal, the recording, will also be of lower quality than the original.
Analog transmission systems are unable to maintain the quality the original has.
Digital Transmission Systems
In the digital world the recording can be transmitted to another place without loosing any quality. An exact copy of the original recording is transmitted. So how come that digital transmission systems don't loose quality when transmitting a signal?
Well..... Actually they do lose quality just like the analog transmission system does.
Surprised? No Problem. Most people don't know that digital signals still need to be transmitted by analog transmission systems. The trick is that a digital system doesn't record analog signals, but encodes analog signals into bits (zeros and ones). A sample is taken many times per second and the size of each sample is written down in bits. For instance a sample with the value of 9 would be 1001 and 11 would be 1011.
The digital transmission system needs to transmit those zeros and ones, and it does this by modulating the carrier wave. Low power for a 0 and high power for a 1 (This is the most simple way of modulating. There are much more sophisticated forms of modulation, but it would take a whole book to describe them all.)
So on the receiving end, it doesn't matter anymore what the quality of the signal is, as long as it still is possible to identify the zeros and ones. Noise in the received signal is no problem. A "1" with noise is still a "1" and a "0" with noise is still a "0". Of course the noise can not be too high, otherwise mistakes would be made and a zero would be received as one or a one would be received as a zero.
So Digital Transmission Systems are better because they eliminate the effect of noise completely. You don't look and listen to a received signal from an original recording, but you look and listen to a reproduced signal of the recording. The reproduction comes from an exact copy of the original recording.
The quality of what you see and hear now depends on your TV and Sound System. A high quality TV and Sounds System will give you high quality Video and Audio. The negative effects of the (still analog) transmission have been eliminated from the process.
Satellite TV makes use of Digital Transmission Systems. What you see at home will always be of Digital no (much less) noise Quality.
