Jonny Greenwood on BBC Radio 4

On the day of the Proms premiere Jonny Greenwood explains where the piece started, with Penderecki. As a student in the 1960s Penderecki studied electronic music, learned about filters and noise generation, and then turned his back on all of it, having decided an orchestra could make those sounds and make them more interesting. Greenwood moves the idea on, and instead of the oscillators of that era he set out to emulate artificial reverbs and delays.

One source is the ondes Martenot, whose speaker sits in a box strung with two dozen strings, so that whichever string matches the note being played resonates in sympathy. It gives a distant, old-fashioned quality Radiohead have used on a record. With 68 stringed instruments on a stage he could do the same at scale, the orchestra becoming a resonant box around a soloist, and later in the piece it emulates digital echoes.

It is not supposed to sound like electronics, he says. It is supposed to be better, because human players cannot be perfectly even across all frequencies the way software can.

He is surprised by how much he enjoyed working with the youth ensemble.