What does 'fade in' signify in sound management?

The term 'fade in' in sound management specifically refers to the gradual increase in volume of sound over a period of time. This technique is often used in various forms of media, including film and theater, to create a smooth transition into the audio, making it more pleasant and engaging for the audience. As the sound fades in, it allows for a gradual introduction, which can help to build tension or set the mood effectively.

The other options present different sound management techniques. Decreasing volume is referred to as a 'fade out,' which would not accurately describe a fade in. Adding echo effects pertains to sound manipulation, enhancing the texture and depth of audio rather than altering volume. Muting all audio completely is a separate action and does not relate to the gradual increase of sound. Thus, the correct understanding of 'fade in' clearly aligns with the notion of increasing volume over time.