Life's Soundtrack, Radio 4

Have you heard the one about optimal hearing?

An investigation into how our hearing and our voices develop over a lifetime, Life's Soundtrack was originally broadcast last year, too soon for the story about foetal iPods that was in the news last week – a belt worn by mothers-to-be transmitting music into the womb. But as the programme's presenter, Dr Trevor Cox, discovered, it would all sound a bit weird in there.

You'll have noticed in swimming pools that beneath the surface everything sounds bassy and muffled. And amniotic fluid also cuts out the middle and higher frequencies. Pregnancy MP3s would be great for dub or grime, but classical music might get lost – bad news for parental hothousers keen to road-test the Mozart-makes-you-good-at-maths theory.

At Sound Science Research in the Hollywood Hills they've been researching "acoustic swaddling", to help newborns sleep. They combined the low, muted rumblings heard by the foetus – the sound of the mother's internal workings, the organs moving round and the swirl of the fluid – with ambient music ripped off from Brian Eno. The babies seem to love it.

Dr Cox went on to explore how the voice changes over time. I thought there might be some attempt to integrate the auditory and vocal aspects of the programme into some larger theoretical whole, but they were kept separate, which was slightly disappointing but probably sensible.

There was interesting stuff about new theories of dyslexia: we've always thought of reading problems as a visual thing, but research suggests it might have something to do with the fact that the part of the brain that codes language overlaps with the bit that codes sound. It makes sense: as you're reading this you're hearing it in your mind's ear.

Elsewhere, for ageing music lovers like me, there was only bad news. Optimal hearing comes at the age of 20: from then on it's downhill. "I sometimes joke we have one day of perfect hearing in our lives," says David Moore of Nottingham University.

Thanks, Dr Moore. I didn't need to hear that.