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DOC-01-TELAS-CRG-4 ASTi ACE Studio Components Reference Guide Rev.M

9.0. Highway 3D Service

The Highways 3D Service is a collection of components used for mixing and

routing audio to hardware output channels. The service provides two approaches

for audio mixing - Gain-Mixing and 3D Soundfield Reconstruction - making it

useful for a range of applications, from routing communications audio to operator

headsets to immersing listeners in a 3D audio environment.

Gain-Mixing

Gain-Mixing is the simpler approach and represents the more traditional way of

mixing audio. Sounds are sent to a set of output “highways” using a set of gains that

are driven by the host or calculated in the model. Gain-Mixing using the Highways

3D Service allows the developer to easily route audio from simulation models to

hardware models, making it an attractive alternative to using connectors and

busses.

Soundfield Reconstruction

The 3D Soundfield Reconstruction (SFRC) is a sophisticated method of processing

sounds to make them appear to come from somewhere in 3D space around the

listener(s). Sounds are assigned (x, y, z) positions relative to the listening or

“reference” point. The Highways 3D Service then filters and mixes each sound

based on its position in order to encode the sound into a virtual 3D sound

environment or “Soundfield”.

Once all the sounds are encoded, the Soundfield is decoded for playback in stereo

headphones or an array of speakers. If decoding to headphones, two output streams

are output for the left and right earphones. The head's orientation is used in this

calculation if it is available from a head-tracking system. If decoding to a speaker

array, the service outputs one audio stream for each speaker, taking into account the

speaker's (x, y, z) position.

All positions used in the service must be specified in meters relative to the listening

or “reference” position. The reference position should be the central listening point

of the simulator, such as the midpoint between the pilot's and co-pilot's heads. This

ensures the service will render the sounds in a way that sounds best to all listeners.

Use the following coordinate system when calculating the relative positions of

sounds and speakers:

The 3D positioning algorithm used by the service calculates a contribution from

each speaker for each sound, even if the speaker is not precisely in the right

direction. This results in realistic and immersive reproduction of many types of

sounds.

If a sound is to output only through one speaker, use gain-mixing or connectors and

busses instead of SFRC.

(positive = left)

(positive = forward)

Sound Field

Reference Point

units = meters

(positive = up)