Hampicke 2015. Hampicke, Evelyn (2015). "Jules Greenbaum". CineGraph – Lexikon zum deutschsprachigen Film (in German). Cinegraph.de. Retrieved 8 October 2022.
UFA had acquired the German rights for an early sound film system, Tri-Ergon, in 1924. The Tonbild Syndicate AG (Tobis) - with German, Swiss and Dutch backing - acquired the Tri-Ergon rights in 1928, and merged with Klangfilm (a partnership between Siemens & Halske, AEG, and a Dutch recording company) to form Tobis-Klangfilm in March 1929. Source: Gomery 1976, pp. 53, 54. Gomery, Douglas (1976). "Tri-Ergon, Tobis-Klangfilm, and the Coming of Sound". Cinema Journal. 16 (1). University of Texas Press, on behalf of the Society for Cinema & Media Studies. JSTOR1225449.