Greene, David Mason (January 1995). "Mozart's The Marriage of Figaro by Hans Hotter, Helena Braun, Erich Kunz, Irma Beilke, Gerda Somerschuh, Gustav Neidlinger, Res Fischer and Josef Witt under Clemens Krauss". American Record Guide. 58 (1): 254. ProQuest223426135.
Härtwig, Dieter (1965). Rudolf Wagner-Régeny: Der Opernkomponist [Rudolf Wagner-Régeny: The Opera Composer] (in German). Berlin: Henschelverlag. p. 48. OCLC8740131.
Kolodin, Irving (1966). The Metropolitan Opera, 1883–1966: A Candid History (4th ed.). New York: Alfred A. Knopf. p. 488. OCLC273914.