What is In-Up-Down-Out means ?

• A. The voice of a conversation that is carried out directly in front of the microphone to create the impression of an indirect conversation (from a distance)
• B. The increment of sound gradually, from slowly then getting louder
• C. The music in radio ad goes into standard volume and then decreases, and disappears
• D. The music in radio ad goes into a standard volume and then becomes the background of the ad