stereo sounds are two seperate sounds, one for your left and one for your right speaker, played together with a fixed volume relative to eachother.
e.g. take a moving car sound.
in a stereo file a car moves from left to right. it starts with left speaker = low volume, right speaker = no sound. in the middle of the sound youll have both speakers the same high volume, where the car passes you and at the end youll have no sound at the left and a fading out low volume sound on the right speaker.
in a 3d game enviroment we can render our own stereo/surround sounds.
sound sources can move in this 3d world, in relation to your point of view.
take the example from above.
yull see and hear the car moving from left to right. you will more or less get your sound like the stereo one from above. but if you turn around ingame, the sound will change to a right to left moving sound (and front to rear for surround systems).
but the car sound itself that is used in the 3d world is a mono sound. it has to be mono. you cant move a stereo sound around in a 3d enviroment, cause the left and right channels are fixed.
in RL all sounds are mono sounds! even your speakers are! each single speaker is a mono soundsource in a (real)3d world.
youll only get a stereo sound when you have a speaker that plays the left part of your stereo file and one for the right part, in the right distance to eachother and your ears.
the ingame gunfiresounds that you hear in the first person, aka your own gunfire, are stereo files. they can, cause your point of view in relation to your own gun will never change. thats why your own gunshot sounds more dramatic and intense then the one from your mate next to you. (cause you hear his gunfire as a mono sound in the 3d gameworld, rendered to a sound that fits to his position and distance to you).
and so it is for the bullets that pass near you and triggering the bullet crack sound to play exactly where the event is happen in relation to your position.
so, hopefully now it is not more confusing then before, with me and my poor english trying to explain a more or less complex, technically problem..


