2/4. Russell Davies resumes his exploration of the ancient art of close-harmony singing. The first series, which aired in 2005, celebrated its many variations, including barbershop, jazz, gospel and doo-wop as sung by sacred, commercial, amateur and professional groups. This series features Ladysmith Black Mambazo UK and US jingle performers, Welsh male-voice choirs, cathedral choristers and many other contributors to the art form.