Background sound effects are the essential building blocks of a successful scene. These sounds build worlds around characters and compliment their emotions. Subtle changes in background elements foreshadow events and can build tension leading up to them. In this article, we will explain how we layer our scenes with a host of background elements and how manipulation of these layers provides sonic interest that is often felt rather than heard.
When designing backgrounds, we like to aim for eight different layers. As sound designers, it's important to remember that we have to accommodate sounds that the audience may never see. A good place to start would be using markers so you know where each scene starts and ends, to the frame. We will use a big city as an example... The obvious choices for sounds here would be traffic, people, crowds, and wind. The sounds that we can't see often make the biggest difference. For example, we could have birds, a church bell, police sirens, trains, rivers, plains or live music. Eight layers seem like a lot, but they get filled quickly!
It's always handy to have at least one mono background in a given scene so any discrepancies in dialogue can be masked. This is usually a quiet wind or room tone.
When changing scenes, the layers must fade into the next one by one frame. So, at the start of the shot, there should be a one-frame fade out from the previous scene and a simultaneous one-frame fade in for the forthcoming background effects. This isn't a hard rule, but we find this often gives us the smoothest transitions. Due to this, we checkerboard our backgrounds meaning that a total of 16 tracks are required for this process.
We tend to find that some background sound effects lack a low-end rumble, which is essential for filling space in a scene. Adding a pink noise layer to backgrounds with lots of mid/high content can solve this issue. Selecting a pink noise waveform in a signal generator and applying a low-pass filter can be the perfect space filler. A boost around 60Hz-100Hz usually helps to fill the low-end.
Don't be afraid to add subtle changes to your background effects to reflect or foreshadow certain events or emotions. For example, let's say that there's going to be a big explosion in a city. Adding a drone could be a great way to build tension. Background FX doesn't always have to be natural, sometimes a synthesised effect can complete a scene. Changes in level could also make the explosion more of a surprise. More experimental effects such as distortion could be used to build tension too. It's important to keep these changes subtle though as more obvious sounds would be dedicated sound effects.
If you enjoyed this post please check out our ultimate guide to audio post-production: https://www.344audio.com/post/the-ultimate-guide-to-audio-post-production-sound-design
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