Question

What is the purpose of the first vector in the listener orientation? The tutorials say that the two vectors are ‘at’ and ‘up’, but shouldn’t setting the position already determine where ‘at’ is?

I’m also confused why all of the tutorials set the position to 0,0,0 but set the orientation ‘at’ 0,0,-1.

What am I missing?

Answer 1

Think of “AT” as a string attached to your nose, and think of “UP” as a string attached to the top of your head.

Without the string attached to the top of your head, you could tilt your head clockwise/counterclockwise and still be facing “AT”. But since you can tilt your head, there’s no way for the computer to be sure whether something to the canonical “right” should sound in your right ear (the top of your head faces “upwards”) or your left ear (the top of your head faces “downwards” because you’re upside down). The “AT” and “UP” vectors pin the listener’s “head” such that there’s no ambiguity for which way it’s facing, and which way it’s oriented.

There are actually 3 vectors you need to set: Position, “AT”, and “UP”.
Position 0,0,0 means the head is at the center of the universe. “AT” 0,0,-1 means the head is looking into the screen, and “UP” is usually 0,1,0, such that the top of the “head” is pointing up. With this setup, anything the user sees on the left side of the screen will sound in his left ear. The only time you’d choose something different is in a first-person style game where the player moves around in a virtual 3d world. The vectors don’t have to be normalized, actually, so you could use 0,42,0 for “UP” and it would do the same thing as 0,1,0.

If you do change “AT” and “UP” from their canonical values, the vectors MUST be perpendicular.