HERE'S A DIFFICULT WORD: "quantisation". It's the most difficult piece of jargon you'll come across as a fledgeling beatbox programmer. Bear with me; if you can wrap your mind round this, you'll be well on your way to producing some half-decent drum tracks...

Last month, I explained how Patterns are constructed from individual beats and strung together to form Songs. Patterns may be written by tapping on the buttons relating to the drum sounds in "real time", or by programming the notes one by one in "step time", usually with the help of a graphic aid called a programming grid.

A rhythm pattern an be visualised as a series of steps. You decide how many steps you need in each pattern, depending on the rhythm. For example, a straight 4/4 dance bat will usually require eight, or most commonly 16 steps; some drum machines may allow you to set 32 or even 64 or more steps. A shuffle bat, such as the hip-hop mix of Climie Fisher's 'Rise to the Occasion', requires a number of steps to be divisible by three, so in that case you would choose 24 steps or maybe even 48.

Let's keep it simple to start with, and take a pattern like 'Word Up' by Cameo - one of the most famous beatbox rhythms of all time. This requires 16 steps. The act of setting the number of steps in a pattern is known as Quantising - that hideous word again! In this case you "quantise" to 16, after which the "smallest" note you can set is one-sixteenth of the whole pattern.

Take a look at the programming grids (Diagram O). You'll see that the grids are divided up into 16 columns each. Each column represents one step, and if two dots occur in the same column, they will be played at the same moment in time.

Each line in the grid represents a different "voice" or sound. So, the top line of dots represents the closed hi-hat part, the second the snare drum, and the third the bass drum. The "Accent" line is not a sound but an "emphasis". The secret of good programming lies in setting this line correctly and imaginatively - but for the moment, it's more important to concentrate on the sounds and rhythms themselves.

The two patterns in the diagram don't make sense on their own. They form a repeating pair that starts the track off and sets the tone for the rest of the composition. So when visualising the rhythm, it's important not to think of the patterns separately, but together.

Confused! Believe me, it's a lot more straightforward than it sounds. But how do you program this rhythm! You have a choice of "real time" or "step time", and this is where "quantisation" comes into the picture again.

First of all, let's assume you want to program the rhythm in step time. A set of editing buttons allow you to specify whereabouts in the imaginary grid you want to place individual beats. Typically, you enter the beats line by line, ie. all the beats of a particular sound at once. So, for example, you'd program the closed hi-hat to appear on steps 1, 5, 9, 11 and 13; the snare to appear on steps 5 and 13; and the bass drum to appear on steps 1, 7 and 16 in the first grid, and 1 and 7 in the second.

On playback, the machine will just scan along all the imaginary lines simultaneously and play the beats as it comes to them. The tempo can be set to whatever speed you choose; the higher the number of beats per minute (bpm), the faster the machine will scan.

It's important to understand what "beats per minute" actually means. In this context a beat is not the same as a step; it's better described as the pulse. If you listen to 'Word Up', you'll find yourself tapping your foot on the 1st, 5th, 9th and 13th steps of the pattern; in other words, there are four beats to the pattern, or in conventional terminology, "four beats to the bar". Thus, if you set the tempo to 112 bpm, there will be 112 of these pulses each minute.

This is where programming in "real time" comes in. This allows you to program the patterns simply by tapping the buttons relating to each sound in turn.

Your drum machine will provide a metronome for you to base your tapping on. This metronome will click with the bpm pulse, ie. four clicks per pattern. We'll assume for the moment that your machine is one which only allow you to program one pattern at a time. Starting with the first pattern, the click begins, and you can listen to it until you feel you're ready to start tapping. Choose the sound you want to enter first: I usually put in the hi-hat, but most people prefer the snare to start off with. Hit the appropriate button in time with the metronome for four clicks, then listen back to it. Then enter the rest of the sounds one by one. As you improve, you'll be dextrous enough to enter more than one sound at once. For instance, many people enter the bass drum and snare at the same time.

Quantisation is critical when programming in real time, since the machine will automatically slot your taps into the nearest step. For example, let's say you hit the button for the second snare beat fractionally late: the machine will automatically correct it to the nearest step, which is the one you wanted. But if you hit it over half a step late, it will correct it to the next step along.

The quantisation is crucial because if you are quantised to the wrong value (eg 8 instad of 16), then the machine will correct to the wrong step. Taking the first grid in the diagram, if you are quantised to 8, you won't be able to program the final bass drum beat on step 16 - because it doesn't exist!

There's much more to be said about choosing the appropriate quantisation value. But, on second thoughts, I think that's enough to be going on with...