Blackmail (1929 - Alfred Hitchcock) is particularly interesting film in terms of sound because it was in early years of sound in cinema that it has been made, so early that some cinemas ( studios as well ) where not still equipped with sound equipment. When Hitchcock found there is an opportunity to record some scenes with sound, he reshoot some of the scenes. So the film came out with two version, one with the sound and the other one without. (Talkie version, Silent version) In this case they could show the film in both cinemas with and without sound equipment.
Hitchcock has used some techniques in that early years to make the best of the sound that he could have , such as using the bird sound during the scene that the girl is in her room and it is after the night she committed a crime. the sound is there to add the tension and mental state of the character.