Rather than leave audiences with only the noise of the projector as an accompaniment, theater owners hired a pianist or organist or, in large urban theaters, a full orchestra to play music that fit the mood of the film at any given moment.
Rather than leave the audience with noise of early cinema projectors, theater owners would hire a pianist or organist or a full orchestra to play music that would cover noises of projector. Eventually, musicians would start to fit the mood of the film at any given moment.