Some songs weave in and out of history, surfacing with different singers, in new versions and interpreted in different ways; each adds something new to the layers of meaning around the original. The beautiful ‘Song to the Siren’ is one of them. Originally written by folk hero Tim Buckley, over the years it has been recorded by Sinéad O'Connor, Sheila Chandra and This Mortal Coil. Robert added his name to the list of artists in 2002, and here he explains why, and how he approaches performing a vocal for such a famous song…