Signal Theory

There are two basic types of signalling – digital signalling and analogue signally.

Digital signal

Digital signal can be defined as an electrical signal that produces data, stores and processes the data in form of zeroes and ones. This means that digital signals can only accept discrete values. Computers use digital signals.

Analogue signal

Analogue signal on the other hand generates continuous values, leading to continuous wave pattern. Telephone lines use analogue protocols. For a computer to transmit data over the telephone line, a special device (the modem) is needed. The modem (Modulator-demodulator) is a device that enables a computer to transmit data over analogue telephone lines.
The computer stores data in form of zeros and ones (binary digits). A single binary digit is referred to a bit and a set of 8 bits is called a byte. 1024 byte is equal to 1 kilobyte. The coding format for characters represented in binary digit is ASCII. ASCII stands for ‘Standards for American Standard Code for Information Interchange’. ASCII represents numbers using a combination of 7 bits ASCII also has an additional bit called the parity bit. The parity bit is the error-checking bit.

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