Home Computer: Sound of something nasty in the system: Andrew Brown makes a big noise about the multimedia 'add-ons' which give frights and delights to his children

PEOPLE SAY that computers are cold and inhuman, but equipped with modern games they can be every bit as compulsively frightening as Grimm's fairy tales. Both my children have gone through phases of demanding that I play endlessly some game that frightened them. They would insist on watching, either from behind the sofa, or sitting on my lap, ready to bury their head in my chest when a nasty appeared.

The trick is the sound effects. To terrify small children properly, you need to buy a 'sound card', an additional piece of hardware to fit inside the processor box, which converts a machine mute but for the occasional electronic bleep into one capable of loud scarey noises. A second add-on in the pursuit of greater verisimilitude is a compact disk, of which more later.

My daughter was only two when she developed a passion for Ultima Underworld II, a game that involved trampling around endless dank corridors looking for monsters to kill, or, more frequently, be killed by. She calls it 'Sewers', because that is where the actions starts.

On one level, Ultima Underworld is a farrago of mindboggling nonsense. It is the eighth or ninth in a series of 'adventures' set in a Texan's idea of the Middle Ages, in which there is a benevolent ruler called 'Lord British' and characters say things like: 'We are excluded from the day to day management. 'Tis like we are but children here.'

But if you do not read the words and keep the screen at eye level, the game becomes far more impressive. Everything is seen from the perspective of a character moving fluently through a claustrophobic warren of brick-lined tunnels. The creatures he meets are fairly convincingly drawn. Not all of them must be fought: some must be flattered or befriended. But the bad ones make noises. The hero's footfalls echo wherever he walks on dry land; doors creak; monsters hiss and rustle, and crash when they attack you. There is a hideous squelching noise when some six-foot high spider collapses into a puddle of green blood at your feet.

It may not be virtual reality, but it is quite enough to induce nightmares. In fact we banned the game after monsters from it began to populate her fantasy life in the evenings. She was absolutely furious. Sometimes in the middle of the night, when she is having a thoughtful conversation with herself while her parents try with increasing desperation to sleep, she will say: 'I have a game called 'Sewers'. There's an octopus there. And there are headlesses and giant rats and bats and . . .'

Such games take over entire computers as well as people. To run Ultima Underworld II satisfactorily, you need a computer that could handle the accounts of a small African nation - that is, ideally, a top of the range PC 486 system. The game demands 14.5 megabytes of disk space and a great deal of main computer memory if it is to run at all, as well as a sound card.

Some people pretend that such add-ons have business uses - but relax: their only real purpose is to play games with. I spent pounds 80 on an Orchid Sound Producer and another pouns 17 on a lead to connect it to the back of the stereo system. The resulting noises are all that a child of any age could wish for. Of course retailers, when selling such equipment to grown-ups, do not call it 'games-playing add-ons', but instead employ the more sophisticated sounding description 'multimedia'. The second essential ingredient of multimedia is a CD-rom drive. These are specially adapted compact disk players customised for use with computers. They are able to handle the huge quantities of data needed to store pictures, especially if these are to be animated.

Games aimed at small children come as rather a disappointment after the delicious terrors of Ultima Underworld. But there is one improving game which my children delight in: Just Grandma and Me. This is billed as a 'living book': the screen largely reproduces a simple storybook, except that the characters say the words displayed. But they do much more.

It is possible to click on almost any part of the pictures and something unexpected and witty will happen. Hermit crabs tap dance; whales sound in the sea; a fisherman hooks and releases an ocean liner. Click on the picket fence behind Grandma and it plays a xylophone scale all the way down her spine, when she jumps and wriggles.

You can choose whether to have the voices speak in Japanese, Spanish, or English. In fact, there is only one snag with the disk: the English is East Coast American and my two-year old has to have almost every word translated.

SOUND cards are circuit boards which can be plugged into the sockets or 'slots' concealed inside PCs and add a connector at the back of the machine into which audio leads can be plugged to connect to a stereo or speakers. They produce a clear, loud and crisp sound comparable to that of a CD player. They cost about pounds 80 for a simple mono version, and pounds 170 for something that works in stereo.

A wide range of mini-speakers to connect to sound cards is now available, while a growing number of 'multimedia' systems, such as those from Apricot, have stereo speakers built in.