It is one of the most famous sounds in the history of rock and roll.

The clanging, opening chord at the start of the 1964 Beatles hit A Hard Day's Night is instantly recognisable.

The Beatles in the 1964 rock film, A Hard Day's Night.

Yet, as many musicians have discovered, every attempt to reproduce it seems to sound wrong.

A British mathematician now claims to have got closer than anyone else to solving the decades old musical mystery.