Three years ago, the Alchemy festival featured the first performance by the remarkable British-based Bengali sarod player, Soumik Datta, and the British-Austrian percussionist Bernhard Schimpelsberger, who went on to win deserved praise for their debut album, an instrumental set that mixed atmospheric and rousing compositions. This week, the Circle of Sound duo release their second album, Anti Hero, and launched it with a concert at this year's Alchemy.

The new album marks a changed musical direction, and not all the new experiments were successful. The duo have expanded into a band, and for this gig were accompanied by double bass, played by one of their two new singers, Fiona Bevan, and keyboards. A violinist and cellist completed the lineup. The set began with the title song from the new album, with Datta standing to play his electric sarod as if he were a rock guitarist, complete with an array of effects pedals. The sarod is a glorious and versatile instrument that looks like a 19-stringed cross between a guitar and a banjo, with a fretless metal fingerboard. It can work well in a band setting, but here, these extra musicians simply weren't needed.

The first half of the set was patchy, with songs that veered between Asian-flavoured pop and ambient styles, enlivened at times by Datta's inspired solos. But then two celebrity guests transformed the evening. Nitin Sawhney played delicate, flamenco-influenced acoustic guitar on Skeleton Leaves, which didn't need the added keyboards or vocals, while Anoushka Shankar showed off her exquisite sitar work on an extended duet with Datta on XY. Datta then displayed his finest playing of the night, switching from delicate themes to a rapid-fire sarod anthem, while the encores included a subtle improvisation in which he was joined by both Sawhney and Shankar.