Voice and a guitar make up the skeleton of a song, and in some cases that is all you need; adding more flash just makes the music flabby. Four autumnal releases add up to a masterclass in doing more with less.

John Martyn has made a career of slurring voice and guitar alike into a pastoral, bucolic haze, the musical equivalent of double or triple vision. A new CD, At the BBC, collects several sessions he recorded for the BBC in the 1970s, with less room to rely on studio trickery than on his own albums. But the result still has all Martyn’s tightly wound, overwrought tenderness.

There are two readings of “May You Never”, trite enough for Rod Stewart, which is two too many. But the album is bookended by two extraordinary tracks. “Devil Get My Woman”, from 1973, bounces along with an echoplexed throb, doubled and redoubled as fractally as an Escher landscape, sounding 10 years ahead of its time. And “Small Hours”, from 1978, shimmers in and out of focus, with Martyn’s singing fragmentary and whispered.

Bert Jansch has been releasing guitar albums for more than 40 years. The Black Swan sees him chaperoned by a raggle-taggle band of the new folk stars who congregate around the Californian Arthur magazine and serve as courtiers to Jansch’s contemporary Vashti Bunyan: Noah Georgeson produces, members of Espers back, and the inescapable Devandra Banhardt sings superfluous backing vocals.

Also present as a singer is Beth Orton, an acid-folk-electronica singer whom the folk police see as anathema. Her voice is as flat as a fen, and her sense of tune impressionistic, to put it politely. None of this stops her being a compelling singer. Here, on “Katie Cruel” and, in particular, the lazy melancholic swing of “When The Sun Comes Up”, she sets off Jansch’s intricate guitar embroidery just distinctively enough to banish fond memories of The Pentangle. Yet the best part of The Black Swan comes when Jansch does his own singing, on “High Days”. “It didn’t matter then/And I guess it doesn’t matter now”, he sings, with precisely the right combination of resignation and resilience.

Ani DiFranco’s recent albums have been as obsessive-compulsively funky and scratchy as eczema. Reprieve has calmed down a lot. The bohemian one-woman industry started work on the album in New Orleans, fled from Hurricane Katrina, leaving the master tapes behind, and waded back to rescue them three days later. It is no coincid-ence that the album feels wavy, drowned .

“Millennium Theater” encapsulates the mood of that class of American who feels a sense of personal affront, as if the country had been stolen behind their backs. The villains of the piece, “Halliburton, Enron, Chief Justices for sale”, promote politics as spectacle; they “slip the little prince in the back door”. A kaleidoscope of 21st-century Americana slides by: pollution, melting ice caps, orange alerts. “The resistance is just waiting to be organised,” she sings, like someone trying hard to convince herself.

Moussu T e lei Jouvents set Occitan nationalism to music, something you don’t hear enough of. Most of Forever Polida has the familiar Mediterranean Ramblas swagger, shouts and exhortations over an idle acoustic vamp. When this comes off, as on the comedy-cannibal caper “Sur La Rive”, it is simply good fun. But on “Sus L’Autura” the atmosphere changes abruptly. Over a duet between banjo and slide guitar, Tatou sings unaffectedly about the view from a pine-covered Provençal clifftop, gazing at dolphins, and birds flying north with the news from Algeria and clandestine migrants: a sea where north Africa seems closer than Paris. And the Occitan lyrics, harsher and stranger than French, give the song the air of a medieval troubadour’s lam-ent. If only all national anthems were this understated.

‘At The BBC’ is released by Universal. ‘The Black Swan’ is on Sanctuary, ‘Reprieve’ on Righteous Babe, ‘Forever Polida’ on Harmonia Mundi