Hear ye, hear ye . . .

TheLastStraw: It may have escaped your notice until now, as it had mine, but apparently all adults are at least partially deaf.

From the age of about 20, the human ear deteriorates, and its ability to detect very high frequencies is the first casualty. This explains many things. Like why - without getting into gender issues - some of us have difficulty hearing people with higher-pitched voices, especially when they suggest that today would be a good time to mow the lawn.

Inevitably, technology is responding to the issue of adult hearing deficiency, and in surprising ways. One example is the news this week of the Sonic Teenage Deterrent (STD), an invention designed to discourage young gangs from loitering outside shops and other public places. The device works by broadcasting a noise that, in tests, makes people under 20 cover their ears in distress. No, it's not the new Enya album. It's a series of 80-decibel sound bursts at pitches of up to 16khz; and its (alleged) beauty is that adults can't hear it at all.

The inventor must have seen the film Mars Attacks in which, as you may recall, humans are saved when the otherwise invulnerable invaders are found to have a fatal intolerance to the music of Slim Whitman. Exposed to loud broadcasts of the country singer's uniquely high-pitched voice, the Martians' heads explode. It couldn't work in real life, of course. One of Slim Whitman's drawbacks is that humans of all ages can hear him too.

So the STD is a breakthrough, of sorts. According to the Daily Telegraph, it sounds to young ears "like a demented insect or a very badly played violin". This is confusing. I have no idea what insect dementia sounds like, but as the father of a neophyte musician, I can confirm the inner ear retains a capacity for violin-related suffering into middle age. In fact, only younger ears seem indifferent to the noise. But anyway, the STD seems to work and, unhampered by its unfortunate acronym, has been endorsed by British police for use in "trouble spots".

A more charitable development in sound technology is the increased deployment by opera houses of microphones. According to a recent article in the New York Times, this is in part a response to hearing loss among the "Woodstock generation", whose ears have been damaged by loud rock music. Microphones have always been part of rock, of course. But until recently they had no place in opera, and purists would say they still don't.

Electronic sound enhancement is to opera singers what drugs are to sport. Traditionally, opera fans were secure in the knowledge that Luciano Pavarotti had reached the top of his profession thanks to nothing more than talent, hard work and vast amounts of food. Similarly, when the tenor Stefan Zucker set a world record (wind assisted) for singing a high A during a performance of Bellini's I Capuleti e i Montecchi, nobody wondered whether he was on something (other than a stage).

But the increased use by concert halls of sound-enhancement systems threatens to change this. The cautionary tale, argues the NYT, is the Broadway musical. Sixty years ago, the paper recalls, the musical was a word-driven art form, in which "stylish singers with small voices, like Fred Astaire" could thrive. Orchestrations were light and audiences listened carefully. Then, like a mystery training programme introduced by the coach of a 1980s East German female shot-put team, amplification took over. Audiences became less alert, lyricists less subtle, and the Fred Astaires found themselves struggling to compete with a generation of musical Ben Johnsons, beefed up on microphones and brash orchestration. Musicals got bigger and schlockier, reaching their "nadir" (the NYT claims) with such 1980s melodramas as Phantom of the Opera and Miss Saigon. The article adds: "Whatever one thought of the music in those shows, no-one paid much attention to the sappy lyrics." The NYT writer concludes by predicting the literate musical's comeback. I'm not so sure. Just last month, Andrew Lloyd Webber broke his own Broadway record, when Phantom played for the 7,486th time, beating the old mark set by Cats. Critics can't prove anything, unfortunately, but it's unlikely that a lyrically subtle musical will get anywhere near these records.

The really bad news is that the "iPod generation" may be going the same way as those before it. According to Newsweek magazine, more than five million US children under 19 now have some hearing damage. This has implications for the long-term success of the STD. But the good news is that there are humane alternatives for dispersing gangs. Britain's Co-op stores broadcast Mozart and Vivaldi outside their shops, and it seems to work.