Lesson 1: Definitions.

These days the words "Digital Audio" are hardly ever mentioned because, with the abundance of computerised devices, everything is digital, so digital is the norm and any mention of "Analogue" is language from the archives. Never-the-less, analogue devices still exist as long as we live in the real world. So, what is an analogue device and how is it different to a digital device.

The answer is easiest explained by looking at a boat riding the waves in the ocean. When the boat is on the crest of the wave then its at its maximum height, and when its in the trough it is at it's minimum height. There are then an infinite number of points between the lowest and highest points. If we were to make a graph of every point between the minimum and maximum then we would have a continuous line. This graph is an analogue representation of the boat's height as it rode the wave. Analogue Path In the previous paragraph I used the words "as long as we live in the real world" and that is because sound in the real world comes to us as waves, analogue waves, and until they invent a device that is able to take a digital signal and inject it directly into our brain we will need devices to convert the analogue signal into digital, and digital back into analogue so we can hear it.

All digital devices use a "clock" to control the switching of the internal circuits. You have no doubt heard of computers that operate at speeds in Giga hertz. That is the speed of the clock that controls the internal processes. Well, digital audio devices also use clocks when they are processing incoming audio signals, and at predetermined clock times the wave is "sampled" to determine the level at that point in time. This device is referred to as an Analogue to Digital (or A/D) converter. This level is returned and stored as a combination of numbers, one to represent the level, and the other to represent the point in time. When we want to listen to the stored information we need another device called a Digital to Analogue (or D/A) converter.


Digital Path

Ironically, any time digital information is stored (CD, DVD, or even the computer hard disk), or transmitted over long distance (TV, radio, internet, etc) it is actually converted into an analogue format so it can be stored/transmitted, and returned to digital at the other end. That is exactly what your internet Modem is; a digital to analogue (modulator) and analogue to digital (demodulator) converter. By putting the two words together (modulator and demodulator) we get the word Modem. Welcome to the real world !!!



We're almost ready to move on to the lesson about sample rates and bit rates. You'll soon be able to click here to go to the lesson about the sampling process, or click here to return to the Analogue and Digital Audio index page..