Although reminiscent at times of Jaco-era Joni Mitchell, this double-album – the fourth collaboration between Julie Tippetts and Martin Archer – feels genuinely experimental. And it's often an exhilarating listen, the singer and the multi-instrumentalist (and their 12 excellent fellow musicians) attempting to explore genuinely new ground. Tippetts has a remarkable voice, of course, her melodies here are appealingly ‘serpentine’, to borrow the title of one of their previous collaborations. The whole edifice exists right at the edge of song form, hence the echoes of Joni Mitchell – or indeed of 1970s Robert Wyatt, who still regards Tippetts' 1975 album Sunset Glow as a companion piece to his own Rock Bottom. Yet it is in the nature of experiments that the success rate falls below 100%. There are moments – and these are usually the moments at which Tippetts moves from singing into spoken word – when Vestigium falls suddenly flat, making for a frustratingly patchy overall experience.