How do time signatures work?

Everything You Ever Wanted to Know about Classical Music, Sunday 1 February, 9pm.

This week, Catherine Bott asks: 'How, exactly, do time signatures work?'

Most people know that a 3/4 oom-pah-pah rhythm is great to waltz to, but it’s also the time signature for Ravel’s Bolero.   

What happens when composers start playing about with 9/8 time – as in Wagner’s Ride of the Valkyries – or 5/4 in ‘Mars’ from The Planets by Holst?