Anonymous 4 are retiring. Not immediately, but the American all-female vocal quartet have announced their decision to go their separate ways following the 2015 16 season. After three decades and over 20 albums it’s still a farewell that comes before time, as their latest release – vocals as clean and programming as original as ever – makes poignantly clear.

Fittingly enough, ‘1865’, released to coincide with the 150th anniversary of the end of the American Civil War, spends a lot of time brooding on goodbyes. Songs from stage, parlour and backwoods explore the separation and loss of the war both from the perspective of the soldiers (on both sides) and the women left behind.

The risk with a project like this is one of tone: inevitably many of the songs tread similar emotional ground, and in a style whose emphatic sweetness can all too easily curdle in a contemporary ear. Anonymous 4 address this neatly by adding the wonderful Bruce Molsky – fiddler, guitarist, banjo player and vocalist – to their number, roughing up the neatly scalloped edges of the music when things threaten to get a bit too precious.

There are still plenty of ballads to the likes of Evelina, Nelly, Aura Lee (the original source of Elvis Presley’s ‘Love me tender’), some tackled in close-harmony girl-group style, and others with banjo accompaniment. Most successful, however, are the folk and church-influenced numbers – the simplicity of an unaccompanied ‘Abide with me’ and ‘Shall we gather at the river’, the intimacy of Molsky’s ‘Brother Green’ accompanied on his fiddle, and the straight-up beauty of the duet ‘The True Lover’s Farewell’. There simply isn’t a recording of comparable quality in this repertoire.