“Beauty is the renunciation of habit,” wrote the composer Helmut Lachenmann, and the Studio for New Music ended its concert “Echoes of Theatre” on one of the bleakest notes in musical history. “I am sorry that I am not fire” – with this line from Alexander Vvedensky’s 1934 poem “I am sorry that I am not a beast” ends Edison Denisov’s “The Blue Notebook” (1984), the main work of the programme (marking the 95th anniversary of the composer’s birth). It alone made it worth coming to the Rachmaninoff Hall on a Friday evening, in case anyone happened not to – though the hall was full. Next door to the Rachmaninoff Hall, in the Small Hall of the Conservatory, the still unpublished “The Blue Notebook” was performed almost forty years ago.