One iconic black box has probably more than anything else come to define the sound of rock - the Marshall amplifier. It has been, quite literally, behind some of the greatest names in modern music.

It all started in 1962 when drum shop owner Jim Marshall discovered the distinctive growl that gave the electric guitar an exciting new voice. Music got a whole lot louder as young musicians like Clapton, Townshend and Hendrix adopted the revolutionary 'Marshall Sound'. The electric guitar now spoke for a new generation and the genre of rock was born.

Soon Marshall stacks and walls were an essential backdrop of rock 'n' roll. The excesses of rock machismo were gloriously lampooned in the 1984 movie This is Spinal Tap. In an extraordinary piece of reverse irony, it was this comic exposure that rescued the company from financial meltdown.

With contributions from rock legends like Pete Townshend, Lemmy and Slash, plus an interview with the 'Father of Loud' Jim Marshall, this documentary cruises down the rock ages with all the dials set to 'eleven'. Show less