et's take a look at sound cards and what they do.

A sound card is one of the few components in a personal computer that does exactly what it says it does: Its job is to play the sounds associated with a particular program or file. This is not as easy as it may first appear. To understand how this is done, we have to have another physics lesson.

You will recall from a previous article, that all stored files are simply representations of information stored as zeroes and ones. This type of storage is called "digital". You will hear the terms digital and analogue used in relation to sound, so let me try and explain what they mean.

Analogue sound is what you might class as pure sound; original sound ? what we hear every day. If it were drawn as a wave-form it would be smooth and have a rounded peak and trough.

The first thing we must understand is that digitally recorded sound is a facsimile of analogue sound ? in other words, it isn't really a recording at all, it is the precise details of the sound described and then stored as bits (zeroes and ones, as we covered a few weeks ago).

When sound needs to be recreated from the digital recording, it is "rebuilt" from this description to sound as close to the original as possible. This goes for all digital recordings regardless of whether they are sound or picture ? they are a reproduction of the original and not the original. Let me try and explain this further: When we describe a location to someone, we can describe it as a map reference.

apping like this can be used in a variety of ways: Suppose I wanted to send you a picture of a square on a piece of paper. If I were to send it to you via analogue methods, I would send you the picture itself. If I were to send you digital data I might do it like this: Take a piece of graph paper, ten squares by ten squares, and start with your pen on the top left of the square represented by two squares down, by two squares from the left. Now, draw a straight line three full squares to the left, then from there, three full squares down, and from there three full squares to the right, and from there, finally, three full squares up. You will have drawn a square on the graph paper, but here's the point: I sent you the square without ACTUALLY sending you anything tangible: Instead I sent you the coordinates from which you could redraw the square ? I sent you a description that you could understand, and from which you could recreate the item being described.

And, guess what? That's it: I sent you the information in a digital way. Therein lie the basics of all digital recordings ? all of them.

That CD you're listening to is not a recording, it's a representation of the description stored on the disc; that DVD you're watching ? that too is a representation of the data described on the disc, that was transcribed there as zeroes and ones from the original source.

OK, back to sound cards: Basically, your sound card needs to do two things: One, translate digitally recorded data into sound recognisable by you and me, sent out via speakers; and, two, convert analogue sounds from outside the computer into digital for storage on disc. So, on your standard sound card you will have a microphone socket to receive analogue input, and a speaker socket and headphone socket to output sound from the computer. Additionally, if the computer has a internal speaker, the sound card will have an internal connection to that too.

Sound cards are measured using the quality of the sound reproduction, which is measured in bits (as in zeroes and ones). This is a measure of their sampling-rate ? the number of zeroes and ones used to represent the sound recorded.

Thus the higher the sampling rate the better reproduction. Therefore, it follows that a 64-bit sound card will produce better quality sound than an 8-bit sound card.