From Corsican polyphony to Jacob Collier, 50s rock and roll and global hit TV series Glee, close harmony runs through music traditions around the world: but nowhere is it more important than in barbershop, famous for its striped waistcoats, bow ties, and comedy parodies. But today over 70,000 singers of all ages and genders participate in barbershop societies around the world, coming together to compete and perform in quartets and larger choruses, enjoying its exuberant and expressive performance style, and revelling in its magical 'overtones'.

With Brian Lynch from the Barbershop Harmony Society in Nashville and members of the BBC Singers, Tom explores what makes it so unique, from its vocal setting to its use of 'just intonation', and discovers the roots of its history, far from the exclusive Ivy League world it's thought to represent.