With FMOD’s Spatializer, just be aware that it’s not a binaural effect, which is fine for speakers instereo/surround but if you’re planning on using headphones and wanting that spatial perception of direction and distance I’d use one of Steam Audio, Oculus Spatializer, or Resonance Audio. Resonance is great for the Switch game you’re working that you’ve posted in other threads about, because it’s got a low CPU cost, but it bypasses the mixer which makes it a last resort for me in most games. I usually default to Oculus though I think Steam Audio sounds the best of the three.
For your car engine, no, you’ll use one event. Do you have multiple cars in the game or is it a player-only vehicle? If there are many, make sure your spatializer is on the master out of the event — this is the only way to correctly use Virtualize instance stealing which you’ll probably want to use on the Switch. (NOTE: if you want to have a spatialized layer and a stereo layer AND want to virtualize, you’d still put the spatializer on the event’s master, turn the volume down to -infinity on the stereo layer, and send it to a bus so that it doesn’t get spatialized.) If it’s a singular vehicle and there won’t be multiples of this same event playing, you can make two tracks in your engine event — one with a spatializer on it, and the other with your stereo content. How to pan the stereo layer: create a parameter, in parameter type choose “Built-in: Direction” and click OK, select the track, right-click on the pan knob in bottom right of screen and “Add Modulation”, draw a curve like this:
That should do it. A nice subtly-panning stereo layer to supplement your spatial layer. You’ll have fun figuring out which kind of source material works well for each layer, and how much you want the pan to move. Although, if you’re going to do a lot of these events, I’d make a Preset. Instead of using the track’s pan, open the Preset browser, and in the effects tab make an FMOD Panner, set it to stereo, right-click the knob and draw a curve. This way it will save project memory and save you time — just use a preset for every sound you want to do this to. In this image you see I’ve made a few presets:
Then you might want to do the same for distance. Just make a gain plugin preset instead of a panner.
Here’s a curve I made for a sound where I wanted the stereo layer to ramp up more, the closer you are to it, but then drop off faster the farther you are.
As for the difference between spatialization and direction, usually spatialization refers to the ability of the listener to perceive direction and distance, and to “feel” the room that the sound exists in. So this is why it’s important to use a binaural plugin like Oculus/Steam/Resonance with an HRTF if it is ever possible that the player might use headphones. And why it’s important to work out the room simulation, whether that involves using the plugin’s features, or sending to a convolution reverb return, sometimes using automation to control how much of it gets sent.