Among Armin’s other books are Stimmbildung oder Gesangsunterricht? (Voicebuilding or Singing Instruction? — the “correct” answer is implicit in the title) and a study of Caruso’s technique from a functional standpoint. He engaged in a prolonged dispute with the eminent Swiss pedagogue Otto Iro, principally over matters of registration. Armin survived the Second World War and settled in Copenhagen, where he maintained his Gesellschaft für Stimmkultur.