THE problem with Tori Amos is that she has too many problems. As Dorothy Parker said, she runs the gamut of emotions from A to B, and in this case A stands for agonised and B for bereaved. I didn't expect her to barrel through a Chas 'n' Dave ditty (although, strange but true, she does two on the B-side of "Caught a Lite Sneeze"). It's just that the undeniably compelling material - such as "Me and a Gun" accompanied only by the hum of the air-conditioning - would have seemed more vivid if there had been material of a different texture set against it.

At the Albert Hall last weekend, the songs Amos played from Under the Pink and Little Volcanoes (EastWest) were all in the same style as those from her latest album, Boys for Pele (think Hawaiian volcano goddess, not Brazilian football god). On a few, there was a glimmer of guitar from Steve Caton. A triangular screen with blurry colours projected on to it hung above Amos's head like a giant, floating slice of pizza. Otherwise it's Tori and her piano, harpsichord and harmonium all the way.

That's not a big part of the problem. Amos certainly knows her way around a keyboard, and she has an extraordinary, madly shrill voice. But it's a one- woman/one-mood show. Even Nirvana's grunge anthem "Smells Like Teen Spirit" is drawn out into a painful lament. Former Nirvana drummer Dave Grohl has denounced this version as "an abomination", but to me it's just amusing, like Mike Flowers Pops' "Wonderwall", or that French and Saunders sketch where they record an operatic arrangement of "I Should Be So Lucky". What makes "Teen Spirit" comparable to these is the way Kurt Cobain's lyrics wilt when exposed to the harsh light of a slow, coherent rendition. Unfortunately, so do Amos's. Her writing is superb because it's so personal, or so her analysts - sorry, fans - will tell you; and indeed, it's so personal that no one but she can understand a metaphorical, stream-of-consciousness word of it. Still, the audience enjoyed themselves. That is, they cheered at the end of each number. During the songs, they sat furrow-browed and serious. As someone other than Dorothy Parker said, she's suffered for her art, now it's your turn.

Twice during his show at London's Jazz Cafe on Monday, Ben Harper jumped up from his chair and whirled around on the spot. His pigtails whipped outwards, turning his head into a propeller, and he very nearly crashed into the six guitars lined up behind him in the process. That was it for movement. For the rest of the night he stayed seated, and who could blame him? I needed a sit-down myself by the end.

While a troubling number of British popsters of Harper's age are squabbling over which is better, early-Seventies revivalism or early-Eighties revivalism, the 26-year-old American has taken a sound that dates back to the birth of the blues, or at least their pre-school years, and made it spellbindingly contemporary and new. He plays slide guitar on acoustic instruments he makes himself (so maybe it wouldn't have mattered if his dancing had damaged a couple of them), in a style he has made his own. It's a catchy, rootsy blues-funk blend, with reggae, gospel and folk influences thrown in, vaguely along the lines of Keziah Jones and Little Axe. On some songs he strummed the simplest chords and sang in a suggestively husky whisper. On others he adopted a soulful yodel, stamped on an effects pedal, yanked the strings so fiercely that he seemed to be making another attempt at trashing his guitar, and produced a range of noises that had to be heard to be believed.

In concert, the music excels that on his last album, Fight for Your Mind (Virgin). Don't be put off an excellent record, though: Harper writes very fine love songs and protest songs. Living just outside Los Angeles, and being something of a one-man American gene-pool (parts black, white, Native American and Jewish), he has plenty to protest about. And unlike the gangsta rappers from his neck of the 'hood, he burns with righteous indignation without losing his cool. A song like "Excuse Me Mr" is all the more persuasive for the subtle groove and the polite tone of the inquiries that lead up to the menacing condemnation: "I'm taking the Mister from out in front of your name/ Because it's a Mister like you puts the rest of us to shame."

It's tempting for critics to make too much of lyrics (they're easier to write about than music), but even if Harper's words were as cryptic as Tori Amos's, it wouldn't have mattered. His band, the Innocent Criminals, responded to each other so well that one suspected they were telepathic. Percussionist Leon Mobley, bassist Juan Nelson, and drummer Oliver Charles took it in turns to show off, then came together to complement Harper perfectly. He is so skilful, intelligent, devoted to his art and, let's face it, so damn cool, that he doesn't sound quite like anyone - and he can appeal to everyone.