Digital-to-analog conversion

When the receiving a digital signal like pulse code modulation (PCM), a digital to-analog (D/A) converter is taken in use. This reverses process of A/D conversion at transmitter, so that original analog data can be recovered.Why to convert a signal to digital form in 1st place, if it is going to be changed back to analog form at receiver? The reason behind it is that the digital signal is inherently simpler than the analog signal, in sense which is less random.  Therefore, a digital signal resembles noise less than an analog signal.It is good to make a signal as different from noise as possible, in as many ways as possible. This is because more different a signal is from unwanted noise, easier it is to separate data from noise, and better is the realizable S/N ratio.

You may think of signal/noise separation in terms of apples, oranges, and a water melon. It takes some time to find an orange in a tub of apples. Think of orange as an analog signal and apples as noise. But assume that there is a watermelon in a bushel basket with apples. You will have no trouble at all in finding watermelon. Think of melon as a digital signal and apples as noise.

Another, interesting feature of digital communications arises when you think of the watermelon in a tub of oranges. It is easy to separate a digital signal from a jumble of analog signals as it is to extract a digital signal from the noise. In the band occupied  by thousands of analog signals, a lone digital signal is picked out easily—far more easily than any analog signals.

In the recent years, digitization has become commonplace not in data communications only, but also in music recording and in video recording. The basic advantage of digital recording is that the selection can be recorded, re-recorded and re-re-recorded, etc., the quality does not diminish.