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Using side-chaining

Dynamic mixing is common in video games. Real-time parameter controls, mix events, and mixer snapshots are frequently used to control audio focus. Another powerful tool for achieving clarity in games is side-chaining.

Side-chaining consists of monitoring the level of an audio signal and using it to manipulate another audio signal. A concrete example of side-chaining occurs in radio broadcasting where a DJ's voice automatically ducks the music volume. In music production, side-chaining is often used to control the energy in the low end of the frequency spectrum when the bass drum quickly ducks the bass volume.

Game application

For games, side-chaining is a great tool for controlling the player's focus when there would otherwise be a cacophony of sound. It also helps to prioritize and clean the mix for objects within the same categories.

When transients from the important sounds are played, side-chaining reduces the volume of less important sounds by following the transient shapes.

This is the important sound. A Meter Effect is inserted on its Output Bus.

These are the less important sounds. The volume of their Output Bus is reduced in response to the increased volume of the metered sound.

A common approach is to set a priority system first among objects of the same categories and then between the categories. For example, following this rule, a game can decide that the playing character’s (PC) weapon sounds are more important than the non-playing character’s (NPC) weapon sounds. Side-chaining can then be set up so that PC weapon sounds duck the volume of the NPC weapon sounds. The weapon sounds between the PC and the NPC are quite similar; but, in this case, the system ensures that the PC sounds are always the main focus for the player.

By extrapolating this idea, a game could decide that nearby explosions should be the main focus over PC and NPC weapon sounds or that critical dialogue should rule over any SFX sounds, including weapons and explosions.

The following chart shows a hierarchical representation of such a system.

Setting up side-chaining in Wwise

It’s easy to set up side-chaining in Wwise using real time parameter control (RTPC) curves and the Meter Effect. The following example demonstrates how signals going through the PC Weapon Audio Bus will automatically compress the volume of the NPC Weapon audio bus in a three-step operation.

  1. Create a Game Parameter: The first operation consists of creating a game parameter (i.e. PC_Weapon_Volume) and providing a range from -48 to 0, which represents a plausible dynamic range for a game. This game parameter will operate as a communication channel between the busses.

  2. Insert a Meter Effect on a bus: The second step consists of inserting the Meter Effect on the bus whose audibility is to be ensured, in this case, the PC_Weapon, and selecting the output game parameter.

    The Meter Effect monitors the input audio signal. When the Effect is used for side-chaining, the Mode, Attack, Release, and Hold parameters are used to slow down the response speed of the output signal and to send smoothed values to a game parameter, in this case, to the PC_Weapon_Volume.

  3. Create an RTPC curve: The third and final step consists of creating an RTPC curve on the bus to be attenuated. In this example, the bus volume is attached to the PC_Weapon_Volume game parameter and then an attenuation curve is created. The "x" axis represents the calculated RMS signal from the Meter Effect, and the "y" axis represents how much the volume of the NPC Weapon Audio Bus will be attenuated.

To build a hierarchy of busses using side-chaining, simply repeat these three simple steps.

Other applications

Since the Meter Effect feeds a generic game parameter, any property that can be attached to an RTPC can be driven by side-chaining. For example, side-chaining can ride the gain of an EQ band to notch a certain frequency band. Other examples include driving the Threshold value of a compressor effect, modifying the LFO frequency of a Flanger Effect, or amplifying the distortion intensity of a FutzBox Lo-Fi Effect.

Wwise side-chaining is remarkably flexible and can be used for various applications. Above all, it's a powerful tool for controlling what a player should focus on in all situations.

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