German-born composer and conductor Matthias Pintscher was a close friend and colleague of Pierre Boulez, following in his footsteps as artistic director of Paris’ Ensemble Intercontemporain, the contemporary music group that Boulez founded in 1972. He conducts the BBC Scottish Symphony Orchestra in the International Festival’s Boulez celebration concert.

Matthias Pintscher: I was never actually Boulez’s student, but we had a very special connection. The first time I met him was at the Lucerne Festival. The general manager had set up a lunch for just Pierre and me, and I was so scared because I felt like I wasn’t ready for him to ask me questions about my music. In fact, we chatted about visual art, films, all sorts of other things. There was an instant level of recognition. After that, we’d sometimes spend a whole day together, just talking about a single piece of music; almost like two nerds.

The French have a beautiful word for a world premiere – création – which shows a creative spirit towards new things. The electronic music studio IRCAM, the new music group Ensemble Intercontemporain, the Lucerne Festival Academy for young musicians, Paris’ new Philharmonie concert hall: none of these institutions would have existed without him, but he was actually building houses for us to live in and for us to fill with music.

On the surface, his music has the most intricate construction, but inside there’s an unbelievable richness of emotion and colour; these waves and washes of sound, on the outside seemingly controlled, but inside always ready to erupt. Some listeners think they’re not qualified to listen to more complex music, whatever that means, like that of Boulez. But of course they are. Everything has evolved and developed over time, and we should embrace that. That’s how you should approach complexity; simply strip off the fear or that educational thing we seem to inherit that tells us we’re never qualified enough to understand it.

Even in his last years, when he was still able to walk, he used to walk fast. We younger people would struggle to keep up with him. That’s the image I’ll always have of him: someone who is always walking forward. Don’t look back, just keep moving forward.

French pianist Pierre-Laurent Aimard was a founding member of Boulez’s Ensemble Intercontemporain and maintained a long and close relationship with him.

Pierre-Laurent Aimard: I first got to know Pierre when he was asked by President Pompidou to found the electronic music studio IRCAM, and he decided to found the Ensemble Intercontemporain too, which I joined as pianist. For me he was a musical god, one of the greatest of all composers, and someone who took music in a completely new direction.

He was a big inspiration for me. Before I met him I’d decided that I wanted to devote a large part of my musical life to living composers and he reinforced me in that belief. Of course he was very famous and influential, but he also helped in a very discreet, modest way; I remember him carrying music stands around or helping out so that a group could play better. He had a very clear idea of what a musician should be, even in an era like ours where fame and celebrity have perverted so many things.

Yes, his music is complex and challenging, but so is Beethoven, so is Bach, and so much other music too. It’s demanding, but what it delivers is irreplaceable. It’s not music written for easy listening, but then I’m not that kind of player either, so I’m very happy that his music exists.

Pierre Boulez: A Celebration, Usher Hall, Lothian Road, Fri 12 Aug, 7.30pm, £12.50–£45; Simpson, Tamestit & Aimard, Queen’s Hall, Clerk Street, Fri 12 Aug, 11am, £9–£31.50.