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Data - Meaningful Information

Analogue Data

Analogue data consists of voltages or currents which are proportional to meaningful information.
Analogue signals can take any value between a minimum and a maximum.
Analogue signals include temperature, pressure, water level, light level and sound.

Digital Data

Digital data consists of well organised binary numbers which represent meaningful information.
Digital signals have only two values.
Low, Off, Zero, False, No - A low voltage less than half the power supply.
High, On, One, True, Yes - A high voltage more than half the power supply.

D to A Converter

This is used to convert digital data back into analogue format.

A to D Converter

This is used to convert analogue data into digital format.

Digitising

This is the process of converting an analogue signal into digital.

Sampling

Converting the analogue signal into a digital value ( usually at regular time intervals ).

Nyquist - Samples per Second

The sampling rate needs to be double the highest frequency in the information signal. So for voice signals up to 4000 Hz, the sampling rate needs to be 8000 samples per second.

Aliasing

Unwanted frequencies or visual artefacts in the digital output caused by the sampling rate being too low. The analogue signal must be filtered to guarantee that all unwanted higher frequencies are removed before converting to digital.