Sound level rises from silence to normal — often without picture cut, to signal scene transition. Audio counterpart to visual fade-in.
You know the scenario: The picture starts to fade in, but the sound only arrives milliseconds later. Or vice versa – the sound swells while the image is still dark. You use this asymmetry to build tension or acoustically suggest a new location before your viewer sees it. The audio fade-in works like an opening door for the ear: silence is gradually broken until the new soundscape is fully present.
In editing, this is achieved using exponential or linear curves – typically lasting 2 to 5 seconds, depending on the emotional pace of the scene. A fast fade-in feels abrupt, almost surprising; a slow fade-in draws you into a space as if you were moving yourself. You can also use this technique in reverse: an audio fade-out initiates the cut while the image is still visible. It's particularly valuable when transitioning between spatially very different locations – for example, from a quiet office to a bustling train station. The sound prepares you mentally before your eye registers the new environment.
Practical applications are constantly seen in TV documentaries: a voice or ambience swells while the camera still lingers in the old scene. This creates continuity without "tearing" the image. You need either a separate audio track for the new location or you mix the ambience tracks in parallel during recording. The audio fade-in is particularly elegant when combined with a visual crossfade – meaning sound and image overlap with a time delay, creating a transition sound instead of a cut.
Pay attention to the frequency characteristics of your fade-in: If you start low (sub-bass or room tone), it sounds more organic than a fade-in that begins at 2 kHz and sounds thin. In cinema, sound designers consciously use this to simulate spatial depth – you hear the space first, then the action.