In addition to the Audio Bus specified for the audio routing, every Interactive Music or Actor-Mixer Hierarchy object can specify up to four User-Defined Auxiliary Sends. Similarly, an Audio Bus itself can have up to four User-Defined Auxiliary Sends. An auxiliary send allows to send a portion of the audio signal to an additional bus (an Auxiliary Bus) for parallel processing.
User-Defined Auxiliary Sends are used to define static auxiliary sends, directly in the authoring, as opposed to game-defined auxiliary sends, which are mostly defined and controlled from the game, dynamically.
The following illustration shows a sound routed to an Audio Bus that has an auxiliary send volume attenuation of 5 dB, with the sound having two other auxiliary sends. Each auxiliary send has a volume attenuation and is routed to an Auxiliary Bus.
To add a User-Defined Auxiliary Send
Inspect the Properties of an object by double-clicking the object in the Project Explorer.
Drag & drop an Auxiliary Bus from the Project Explorer to the User-Defined Auxiliary Sends list, or...
click the browse […] button to select an Auxiliary Bus from the Project Explorer selector.
Set the send volume to the selected Auxiliary Bus
|Avoid feedback loops|
If the Auxiliary Bus is selected from somewhere lower in the bus hierarchy, then there will be a processing loop of the same busses. This can result in latency and may create exceptionally loud or otherwise dissonant audio.
Auxiliary sends can be used to control environments in the game for simple scenarios. An environment is often defined by the reverberation and the early reflections in an enclosed space. For every sound emitter, the game can control the following elements:
Send volume, which could correspond to the wet portion or the reflected sounds.
Output bus volume, which could correspond to the dry portion or direct sound.
Output bus low-pass filter, which could correspond to how much the sound is obstructed or occluded, affecting the frequency response of the direct sound or dry portion.
Attaching a Game Parameter to the first two values allow you to control the amount of dry and wet signal, per game object. The game would then calculate the distance separating the listener and the sound emitter and assign that value to the Game Parameter. In the Game Parameter assignation, the RTPC curves will define how the wet and dry portions of the signal evolve over the distance.
Attaching a Game Parameter to the Output bus Low-Pass Filter would allow you to control how much the sound is occluded or obstructed, from game values.