"OUR TOP of the line model has rain, babbling brooks, a waterfall and assorted surf sounds, and it has a control so that you can change how fast the waves break and how big they are," says the vice president of marketing.

"And you can add seagulls. And choose to have them real close or real far away down the beach. Our newest sound selection is called `Country Evening', with crickets and peepers, those little tree frogs that make noise in the springtime - do you have them in England?"

Enter the sound conditioner, a small plastic unit the size of a video cassette, which claims to replace the maddening racket of modern life with a soothing overlay of unobtrusive chirrupings and gurglings, or the soothing whoosh of white noise.

The Marpac Corporation, of Blue Clay Road, Wilmington, North Carolina, has recently opened an office in London as the start of a drive to bring sound conditioning to Europe. "Marpac is the biggest manufacturer of sound conditioning equipment in the States, and probably the world," Robert Sheehan, Marpac's marketing man, goes on. The company, which employs 25 people, was founded by a James K Buckwalter over 30 years ago. Mr Buckwalter, a frequent traveller, was used to the constant whirr of his electric fan at night; without the comforting sound to soothe him to sleep, he suffered from insomnia.

"As with many brilliant ideas, the thought came from his wife," says Mr Sheehan. "She suggested he come up with something to mimic the noise, and he came up with a dog dish with holes in, with a little motorised fan inside, which he could take with him."

Marpac's range today is a far cry from that humble perforated dog dish. "The sounds in our machines all fall into the category of white noise - they are very repetitious, and the brain tunes them out," Mr Sheehan explains. "You get used to the sound within a few minutes, and only notice it when it stops. Like air conditioning, it's a way of changing the environment to one better suited to our condition as human beings."

Rushing wind, breaking waves and chirping tree froglets do not come cheap. The basic sound conditioning unit (to be marketed in the UK under the brand name Marsona) costs pounds 99.95, while the sophisticated model retails at pounds 149.95. So why not just buy a pair of earplugs?

"That's a tough one to answer!" says Mr Sheehan genially. "Environments can be too quiet as well as too loud." Apparently research has shown that complete silence is as bad for the nerves as noise.

Marpac's customers are light sleepers, from colicky babies through to octogenarians - according to Mr Sheehan around 10 per cent of the American population has a sound conditioner. "And almost every psychologist and psychiatrist in the US has one of these machines in their waiting room or hallway, to mask conversations for reasons of confidentiality. They're discussing real sensitive subjects, and the sound conditioning stops them being overheard. They're used in offices for the same reason - you can hear the person in the next office, but you can't hear what they're saying."

Simon Wigglesworth has the task of convincing the European market that sound conditioning is a necessity. This may not be easy.

"When I try to explain what sound conditioning is, people tend to be dubious and think of it as a very American concept. It's a question of education - like ionisers, they sounded like products that wouldn't work, and now they're quite standard. The first thing people always ask is whether they'll be able to plug them in over here."

Transatlantic customers are so overjoyed with their units that they break into verse. "The traffic noise is gone/ The jets are too/ We sleep all night/ Marsona we love you!" testifies DW of Winnipeg in the company brochure.

Ron Stephenson, a casting director who lives in Paddington, came across sound conditioning in the States, and was one of the first customers in this country. "These machines are addictive; you get used to sleeping with one on because it's so quiet and peaceful and still - nothing can jar you awake. I carry mine with me on trips."

So could sound conditioning be the instant solution to snoring spouses, noisy neighbours, barking dogs, roaring traffic, screaming children, rock festivals, or living next to Heathrow?

The Department of the Environment, responsible for dealing with noise issues, is unconvinced. "The Building Research Establishment is looking into some technical thing that squashes noise, but it works by bouncing vibrations back on themselves," said a spokeswoman, rather dubiously. "Sound conditioning? I'm afraid no one here really knows anything about it."

! For details of sound conditioners, write to Marsona Europe, PO Box 4027, London SW6 2XW