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XPLMSetAudioCone

XPLM_API FMOD_RESULT XPLMSetAudioCone(
                         FMOD_CHANNEL*        fmod_channel,
                         float                inside_angle,
                         float                outside_angle,
                         float                outside_volume,
                         FMOD_VECTOR*         orientation);

Set a directional cone for an active FMOD channel. The orientation vector is in local coordinates. This will set the sound to 3D if it is not already.