It is difficult, these days, to be genuinely astonished by new music. But every so often there's a song that stops you in your tracks. And for many in the past few weeks it's been the sound of a bleakly soulful baritone against a funereal drum. It sounds like something approaching the elegiac tone of Johnny Cash in the twilight of his life, but in the intermittent soaring of the vocal, there's something comfortingly familiar.
This wonderful song, What Good Am I, was produced by Kings Of Leon's Ethan Johns. It has, therefore, immediate cool cachet. But the singer is Tom Jones. Yes, really. The Tom Jones of knicker-throwing fame, of Delilah and Sex Bomb. And in turning his back on his pop sounds, he's following a growing trend of elderly musicians going back to much simpler roots. Jones's late-period musical conversion is undoubtedly modelled on the staggering upturn in the late Cash's fortunes as he entered his sixties. It's barely remembered, these days, that Cash had been churning out album after album of underwhelming country music throughout the 1980s. By 1991 he was in the musical doldrums, his record company pressing only 500 copies of his album from that year, The Mystery Of Life.
So when Rick Rubin - the producer more readily associated with the Beastie Boys and Metallica - came calling for Cash it seemed, initially, a strange marriage. But it was to prove a career-defining move; Rubin simply sat down with Cash in his Tennessee shack and asked him to record stripped-down songs from his own back catalogue. Embellished with tunes from Tom Waits and Leonard Cohen, 1994's American Recordings was widely hailed as Cash's best record since the 1960s, recapturing the sheer emotional power of a voice that was burned into musical history. There have since been another five American albums - listening to Johnny Cash in this intimate form never seems to lose its allure.
Jones doesn't quite manage anything as powerful on his new album, Praise & Blame, but the idea is the same, drawing from the traditional American spiritual repertoire. There are, he says, themes of "choice and consequence, responsibility, struggle, temptation, good and evil". Quite a departure from "What's New, Pussycat?", you'll agree. But the record really does feel like a look back on a life well-lived, full of remorseful, ruminative material. And Jones follows another elder statesman of pop influenced by the Cash/Rubin success story. Neil Diamond liked American Recordings so much he asked Rubin to do the same for him. It was a similarly reinvigorating experience, the easy-listening hits of Sweet Caroline eschewed for a more back-to-basics approach on 2005's 12 Songs.
Unsurprisingly, he had his most successful album in years. The follow-up, Home Before Dark, repeated the trick: it wasn't quite as good but still made Diamond, in June 2008 and aged 68, the oldest performer to have had a No.1 record in the US. Which is rather healthy, all things considered. It suggests that we actually like our favourite artists to shift gears, to try something different rather than peddle the same old shtick, album after album. And these records have an unspoken power to them that comes from the well-worn life lessons of their makers.
But laying themselves bare in this way is still a gamble. Cash wanted to prove a point - he had always wanted to make sparse, acoustic records and felt he didn't have the backing, while the sombre mood of Diamond's album reflected his frequent battles with melancholy. As for Jones, he truly feels it's a return to his spiritual roots of singing in the Welsh valleys. "This is stuff that I listen to, that I've always liked," he told The Guardian.
So perhaps it wasn't entirely unexpected that David Sharpe, the vice-president of Island Records - Jones's record company - should have written recently in an e-mail leaked to The Sunday Times: "Imagine my surprise when I walked into the office this morning to hear hymns. My initial pleasure came to an abrupt halt when I realised that Tom Jones was singing the hymns! I have just listened to the album in its entirety and want to know if this is some sick joke."
But Sharpe of all people should know - from the evidence of Cash and Diamond alone - that this change of direction by Jones is likely to kickstart his career in a way that seeing a septuagenarian prance around with Mousse T, Robbie Williams and Wyclef Jean never really could. After all, it's not unusual ... Praise & Blame (Island) is out on July 26. You can listen to a preview of the album at www.tomjones.com.