Comparison between ADC and DAC

An ADC, or analog to digital decoder, is used to "translate" analog signals into digital signals. An analog signal can take on any value, such as 0.1V, 0.5V, 4.12V, 5V and so on. A digital signal on the other hand can either be "high" or "low", 1 or 0. A computer can only work with digital signals, and therefore you need to convert an analog signal into a digital signal in order for the computer to be able to work with it.

This is what you do when you record sounds or music. Sound is an analog signal and had to be converted with an ADC to a digital signal before it can be used in a compter or stored on a CD.

A DAC, or digital to analog decoder is the oposite of the ADC. Here the digital signal is converted into an analog signal. This is what happens when you play music from a CD-plate. On a CD there are a number of holes, which each translates as a 0 or 1. These are read with a laser beam which is reflected back into a receiver whenever the laserbeam hits a hole. This then counts as a 1. When the disk is spinning it produces a stream of 1s and 0s, which togerther form a binary string, such as 00010111011101. The DAC then converts this value into a analogue signal, such as 1.1V, which is then used to power your speaker and produce audible sound.