FMOD Events are controlled by parameters – input variables that are sent into the FMOD sound engine by X-Plane. Besides the standard built-in FMOD parameters, X-Plane supports two other categories of parameters: cone parameters and DataRef parameters.
X-Plane supports two cone parameters:
xpevent_rel_heading (range is -180 to 180).
xpevent_rel_pitch (range is -90 to 90).
These parameters give the relative bearing of the listener to the event in the coordinate system of the event. The typical use would be to attenuate volume based on the relative bearing to form a sound cone.
An event’s orientation is inherited from the aircraft it is attached to, and modified by the Eulers (psi, theta, phi) in the .snd attachment file.
X-Plane supports the use of any dataref (built-in or plugin-provided) as a parameter. Specific single indices of arrays can be accessed by appending “” (or some other subscripting number) to the end of the dataref name, just like in OBJ animation.
FMOD events can also use wild-card sound parameters. These work by using [*] as the index to the dataref. When you do this, the event reads the index from the dataref that is specified in the .snd file via the PARAM_DREF_IDX directive.
The motivation for wild-card parameters is to re-use a very complex event (e.g. an engine sound) more than once, using the wild-card scheme to access different array indices for different sound instances. For example, in a twin engine aircraft you might use PARAM_DREF_IDX 0 for the left engine and PARAM_DREF_IDX 1 for the right engine, then use sim/flightmodel2/engine/XXXX[*] for your datarefs.