Forward and Backward 3D sound?

I am trying to build a game that uses 3D sound. A sound will play in any of four directions: forward, backward, left or right. It is the users job to decide which direction the sound came from. Sounds like a good plan. Pun intended. While the user can easily decipher whether the sound was on their left or their right, it is impossible to tell when played either forward or backward. Is there some way to fix this? Any help would be greatly appreciated.

There are packages you can buy on the asset store that help a LOT with 3D sound.

But if you’re cheap like me, you might choose to throw a Low-Pass Filter on objects when they’re behind you. That way it sounds muffled, kind of like real life. I ran a playtest on this using full 360 degree freedom of movement and sound placement, and the player caught on pretty quick.