Digital versus analog

A computer works with the binary digital signals, which are fluctuating rapidly direct currents. For the digital data to be conveyed over the telephone or radio circuit, the data should be converted to analog form. In the telephone modem or radio-transceiver modem, this is done by changing digit 1 into an audio tone, and the digit 0 into another tone with the different pitch. The result is an very fast back and forth
 
alternation between the 2 tones. In modulation, digital data can be changed into analog data. It is the type of digital-to-analog (D/A) conversion. Demodulation changes analog signals back to digital ones; this is analog-to-digital (A/D) conversion.If you to pick up a telephone extension while someone is on line with the computer from the other extension, you will hear the analog signals from 2 modems; it sounds like a hiss. But do not make a habit of doing this. It can cause the computer to be disconnected from on line network.