I can hear a letter 'R' when the dolphins sing. Sometimes, I can even hear a letter 'A'!

Antonina, hearing-impaired child

The stands are packed, the crowds already on their feet, and down below, in a pool of rather murky water, the most famous double-act in town is ready for action.

Two dolphins shoot into the air like rockets into space, their silvery bodies gleaming in the midday sun.

More than just a trick

Antonina is deaf but can hear the dolphins singing

Until recently, tricks were just about all that the dolphins, Raddy and Grand, were allowed to do.

However, the two creatures have the chance of a new career away from showbusiness which could eventually benefit millions of people.

Helped by a doctor, 10 deaf children line up by the side of the pool with their backs to the dolphins.

They have travelled from Moscow to help test a revolutionary treatment for deafness.

Musical medicine

One by one, the children remove their hearing aids and wait for a dose of musical medicine.

At the command, Raddy and Grand burst into song. It might not sound the most relaxing melody - but to the deaf children it is, quite literally, music to their ears.

The dolphins could eventually benefit millions of people

They raise their hands in joy. Suddenly, these children can hear sounds and noises that usually they are unable to detect.

"I can hear a letter 'R' when the dolphins sing," says 11-year-old Antonina.

"Sometimes, I can even hear a letter A!"

Ultrasonic waves

Local scientists believe that ultrasonic waves in the dolphin's voices are making all of the difference, helping to stimulate nerve endings in the ear and inside the brain.

Dolphins at work: Creating the sounds which enable deaf children to hear

Viktor Lysenko is director of the Children's Rehabilitation Centre in Yevpatoriya.

"When deaf children listen to dolphins, they hear a new sound, ultrasound, and as a result, the dolphins help deaf children with hearing," he explains.

In a tiny room at the back of the centre, Antonina sits wired up to a machine, 20 electrodes spread from ear to ear.

A computer image of her brain flickers on a monitor nearby.

These types of tests help to pinpoint where exactly dolphin therapy is having most effect.

Medical history

According to Dr Igor Zagoruchenko, there is no doubt that the treatment makes it easier to make sense of sound.

Mr Lysenko: Very enthusiastic about the therapy

"It's like when you clean the lens of a camera," he says.

"The picture doesn't get brighter, but it does become sharper."

Dolphin therapy may not provide a complete cure for deafness. However, it does offer some hope.

That is the reason why scientists in Yevpatoriya are convinced that Raddy and Grand are making medical history by bringing the joy of sound to those whose lives have forever been silent.