If your guitar-playing sounds atrocious, it's probably your technique that needs attention. But it may, just possibly, be that your guitar needs setting-up. We show you how it's done.

IT'S A SAD fact, but a true one. The majority of guitars offered for sale are not set up properly. This means they can be difficult to play, and impossible to tune with any accuracy.

And the problem isn't just confined to cheap instruments, either. Even expensive "name" guitars are rarely set up as well as they could be, making them appear even less good value for money.

Yet with a few basic tools, a little patience, and a little more knowledge, you can do the job yourself. The tools and patience I'll leave to you, but this article should supply you with the basic knowledge you need. You'll also find that an electronic guitar tuner is invaluable in setting-up a guitar. If you're one of those people who doesn't like tuners because the guitar still sounds "out" as soon as you play chords further up the neck, then the problem isn't the tuner - it's your guitar, and it needs setting-up.

ACTION & INTONATION

FIRST, WHAT DO WE mean by setting-up? At the very least, it means adjusting the action of the strings on the fingerboard and then adjusting the bridge to give correct intonation - by which we mean all notes played on each string must be properly in tune, not just the first few frets. Diagram A shows the relevant parts of the guitar, so that you'll know what I'm talking about when we get into making adjustments.

The playing action depends on a combination of factors: the straightness of the neck, the accuracy of the fret heights along the neck, the depth of the string slots in the nut, and the setting of the bridge saddles. In general, the straighter the neck, the lower you can set the action before the strings start to buzz on the frets. But in practice, it's better to have a slight concave bow in the neck, so that if you hold down both ends of a string onto the first and last frets, the string will clear the frets halfway along the neck by half-a-millimetre - about the thickness of a piece of cigarette packet. The reason this is a good idea is that a plucked string vibrates more in the middle than it does nearer the ends, and this slight dip gives it more room to vibrate without hitting the frets.

Most guitar necks are fitted with what is called a truss rod - a thin metal bar running the full length of the neck beneath the fingerboard. The truss rod is securely fixed at one end, but the other end usually has an adjustment nut which can be turned with an alien key or spanner to tighten or slacken the rod. If you can't see the nut, it's probably under a small plate on the headstock or it may protrude from the body end of the neck under the scratchplate.

Turning the nut clockwise tightens the truss rod which lessens the amount of dip, while slackening it allows the tension of the strings to make the neck bow more. In other words, the truss rod is largely responsible for the straightness of your neck. But if your neck has a twist to it when you "sight" along the strings, adjustment of the truss rod will not cure it. In fact, anything more than the slightest twist will adversely affect the action of your instrument, so if things look this bad, consult a qualified guitar repairer.

ADJUSTMENTS

PROVIDED YOU'RE CAREFUL, there's no reason why you shouldn't adjust the truss rod yourself. But you must observe a couple of simple rules. First, always make the adjustment with the correct gauge of strings fitted to the instrument, and make sure they are more or less normally tuned. Second, don't turn the nut more than a quarter of a turn or so before checking the result; if you have to make more than two quarter-turns, leave the instrument alone for half-an-hour to allow the wood to settle into its new position before making any more adjustments. And don't forget to tune up between adjustments, as the change in neck tension will affect the tuning.

So long as your guitar is not too old, the chances are that the frets will be OK. But if you have slight dips worn into some of the lower frets, it might be advisable to use an abrasive stone to grind all the frets down to the same height. This isn't a difficult job, but if you're not 100% confident about doing it, don't struggle with it. Get somebody else in who knows what they're doing, or alternatively, practise on a beat-up old acoustic 'til you get the technique right.

The patented Paul White method is as follows. Buy a straight, fine carborundum stone around six inches long, and make sure it's straight by checking it against a steel rule. Remove the strings from the guitar. Then hold the stone firmly against the tops of the frets and run it gently but firmly along the frets, from one end of the neck to the other.

If you now examine the frets, you'll see that the higher frets are polished by the stone but any low spots will be untouched. Also, because the frets have a gentle curve over the width of the fingerboard, you'll have to run the stone along the frets several times in slightly different positions to cover the full width of the neck. If the low spots are relatively minor, you may find that a few minutes' working with the stone will level them out. But always run the stone the full length of the neck, and keep it tight against the frets. Once the levels have been corrected, run the stone gently along the length of each fret so that the polishing marks run the length of the fret, rather than across it. This will prevent nasty squeaking noises when you bend strings.

Using a stone on the frets in this way is sometimes known as "dressing" the frets, but don't use it to make major changes in fret height, or you'll end up having flat frets with sharp edges. If any frets are particularly low, it's better to have them replaced and then get the repairer to level the remaining frets for you.

BRIDGES & NUTS

ONCE YOU'VE GOT a reasonably straight neck with no unacceptably high or low frets, the next job is to clean off all the muck with a damp cloth, wipe over the woodwork with some spray polish and then fit new strings - not the old ones!

Most guitars nowadays have individually adjustable bridge saddles, so you can set the height and intonation of each string separately. Try to set the height so the top E string is around 2mm above the surface of the 12th fret, and the bottom E is around 3mm away. Check there are no buzzes anywhere along the fingerboard, and if all is well, you could even try to get the action a little lower. Be sure to check that there are no buzzes when you bend notes, especially on the higher frets.

Now it's onto the nut - that simple piece of metal (or plastic) with slots in it that guides the strings from the headstock along the neck. The problem here is that if the slots are too deep, the strings will buzz on the first fret; and if they aren't deep enough, it'll be hard to press the strings down and the action of doing stands a good chance of pushing the strings out of tune. This last point can't be taken too lightly: most of the tuning problems I've fixed for people have been due to a wrongly-cut nut, rather than bridge adjustment.

So let's make a start. First, fret the strings, one at a time, on the first fret and see by how much the strings clear the second fret. Then, play the open string and see by how much it clears the first fret. If the gap is much larger, you may have to cut the slot deeper: do this carefully using a junior hacksaw blade or something similar. You don't need to take the strings off, just lift them out of the slot into the next one. Each time you take a little off, try out the result. Because if you go too far you'll get a buzz, and the only way to cure it will be to replace the nut, or to fill the slot with something like Araldite and then cut it again.

Some guitars have what is called a "zero fret" right next to the nut, in which case it's the height of this fret that's important, not the depth of the nut slots. The theory is the same. The only difference is that you have to use your abrasive stone - or a small file - to reduce the height of this fret until the clearance between the strings and the first fret is as it should be.

Once the nut is in order, it's time to sort out the intonation, but first a valuable tip. Strings often jam in the nut slots, so when you bend strings during solos, the tuning goes out. If you place a piece of PTFE plumbers' tape (available from any hardware shop) over the nut before you fit new strings, the material will be forced down into the slots and will act like a bearing, allowing the string to move freely in the slot.

Another tip. Once you've fitted new strings, grip them tightly about halfway along their length and give them a firm tug. This will remove any slack from either the bridge fixing or the machinehead, and you'll probably find that the tuning goes way out. Retune, and the tuning will be more stable than it would be if you'd just fitted the strings, tuned up and hoped. By giving the strings a really good tug like this, you can fit a new set of strings just before a gig and have no tuning problems.

INTONATION

THIS IS A relatively easy job, but it must be done accurately if your guitar is to play in tune all the way up the neck. The theory is that the note produced by fretting the string at the 12th fret should be exactly one octave higher than the note produced by the open string. Checking this is much easier with a tuner than doing it by ear. If the octave note is flat, then move the bridge saddle slightly towards the neck, retune the open string, and check again. If it's sharp, move the saddle away from the neck. It'll probably take two or three adjustments to get the notes exactly an octave apart, but it's well worth the effort.

Once all the strings are bang on, you're in business. And you'll probably find your playing is easier, and sounds better than it has for a long time.

Listen to a clutch of aspiring bands' demo tapes, and you'll hear a lot of duff recordings. But more often than not, their duffness will be due less to bad musicianship, and more to poorly maintained instruments which buzz or just won't tune up. Get your guitar set up properly, and you've got a real advantage.