Getting an "in key" sound to play with music on another object

I am designing sound for a very musical game where this one particular piece of music has two distinct keys. There will be a sound effect that plays attached to a world object, played in 3D space, as opposed to the music’s 2D space. I want the sound effect to play in the correct key of the music when the music is in that particular key. So let’s say if the music goes ABABAB etc I want the sound effect “A” to play when the music is in the “A” point, and the sound effect “B” to play when the music is in the “B” point. The song continually goes from one key to the other. This particular sound effect can be triggered in-game at any point in the game, and alongside any part of this music.

I am familiar with creating a parameterised sound in Fmod so it wouldn’t be a problem if Unreal sent Fmod the correct parameter, and then Fmod would choose which sound to play based on that parameter. I know how to do that. But what I don’t know how to do is to somehow make Fmod know what point in the song it is playing, and have that point send out a signal to another sound in Fmod that decides which sound to play.

How am I to implement this?

Have a look at callbacks
You might be able to use Timeline markers and access the timeline position if needed as well.