This article explores the several functions of sound and music in documentary cinema. It focuses on the subtle use of sound in its different forms, such as music, sound effects, and dialogue. Given the documentary genre's focus on realism and authenticity, sound design is essential for giving viewers a fully immersive experience and encouraging a greater connection to the topic. This article reveals the transformational power of sound, particularly in its capacity to more vividly express the core of the subject. The first part consists of examining the different types of sound found in movies, their functions and their multidimensional impact, meanwhile the second part is an analysis of two popular documentaries. In doing so, this article emphasizes the importance of sound and music in documentary filmmaking as well as how they may enhance the film's emotional resonance and effect. This article aims to further knowledge of the intricate and dynamic interaction between sight and sound in documentary filmmaking by emphasizing the crucial function of sound.