The first sound film to be made by UFA - and they made the most of it including sounds from almost everything possible, vacuum cleaners, telephones, clocks, passing traffic etc.
Apart from a song that plays over the credits and reprised at the end, all the music in the film is diegetic, the pianist practicing in his room, but heard throughout the house. It's an early stab at realism.
Made in (almost) real-time, recording events of one evening, at least, in a boarding house, shown as if in real time.
According to Robert Siodmak's brother, screenwriter Curt Siodmak, a more traditional love scene between the two leads was shot, but unusable due to an error in exposure. The set had already been torn down, and the film studio in charge of the production, UFA, refused to provide the money to rebuild it, thinking that the film's ending wasn't happy enough to be commercial. Rather than cut the scene, the director asked the cinematographer to film a long take of a cigarette burning to ash and put the sound from the love scene over that shot. The scene became much more overtly sexual due to the symbolism of the smoldering imagery, which critics interpreted as a moment of genius.
Director Robert Siodmak, scouting for new talent, discovered Brigitte Horney in a record store and convinced her to take the lead role in this film.