Pop quiz: who’s the greatest prog rock producer of them all? Is it Eddy Offord, the man who helped construct the groundbreaking sound of ELP and Yes, or John Anthony, who shepherded Genesis, Van der Graaf Generator and Roxy Music to some of their early peaks? Or maybe it’s Terry Brown, Rush’s unofficial fourth member during their 70s imperial phase? Is it a game-changing auteur like Robert Fripp or Brian Eno? Or is it the daddy of them all: the late, great Sir George Martin, without whom the world would sound very different? But there’s another, more left-field contender to consider, one who never worked with any of the genre’s big names but whose collaborations with a generation of experimental German bands would change the course of mainstream music: Conny Plank.