Over three albums and much touring, the Brothers Gillespie, two siblings from Northumberland, have won hearts with a combination of close vocal harmonies and songs carved from the rock, turf and skies of their homeland. On Hirondelle they ally their acoustic folk with two other traditions: that of Provençal, represented by Tant Que Li Siam, a trio who champion the polyphony of the Occitan dialect, and Trio Mythos, a classical three-piece led by Scottish viola player and composer Sophie Renshaw, founded to explore the connections between baroque and folk. Its title is French for swallow (as in the bird), and the album was cut in a week in an East Lothian cottage. The strings of Trio Mythos add piquancy to the two folk outfits; they are mournful on the Gillespies’ Golden One, a Wordsworthian memoir of freedom found in nature, and more jaunty on the Provençal group’s tales of old Aragon and the might of Mont Ventoux. Their own piece, Carolan’s Cup, is sweet and elegiac. The Gillespies get the lion’s share; Tina’s Song is an elegant protest against fracking (“to crack the earth’s bones to make dollars and pounds”), and two odes to Northumberland are yearning and poetic. The swallow’s flight proves an enjoyable adventure.