X3DAudioCalculate

X3DAudioCalculate is a function in the X3DAudio library, part of Microsoft's DirectX audio stack. It performs real-time 3D audio calculations to determine how a sound source (emitter) should be rendered for a given listener, taking into account position, velocity, orientation, and the surrounding 3D audio model. The function is commonly used with XAudio2 to produce spatialized audio effects such as directional panning, distance attenuation, and Doppler shifts.

The core purpose of X3DAudioCalculate is to translate the geometric relationship between a listener and an emitter into concrete mixing data that the audio engine can apply. Given a 3D audio state handle, a listener descriptor, and an emitter descriptor, the function computes results that typically include a channel-mix matrix (mapping the emitter’s output to the target speaker or channel layout) and optional auxiliary data such as Doppler factors and attenuation values. The exact outputs depend on the requested calculations, which are controlled by a set of flags supplied to the call.

Usage and context: developers call X3DAudioCalculate once per emitter per frame (or as needed) to refresh the spatial rendering data. The resulting matrix is used by the engine to scale and distribute the emitter’s sample data across the output channels, while any Doppler or attenuation information can be applied to adjust playback rate and volume. X3DAudioCalculate is Windows-specific and relies on the X3DAudio runtime included with the DirectX SDK or the platform’s DirectX runtime.