hi I saw a trailer by battlefield bad company and i understand in game is a HDRAudio what is a HDRAudio? and how is a technical programming for HDRAudio do is a refrence or article for this work?

The idea is to dynamically change the volume depending on what is being played at the moment. When only quiet sounds are played, the volume is increased to allow players to hear all the details of the sound. Then when an explosion or some other very loud sound is about to be played, the volume is decreased so the explosion would sound about as loud as the previous sound. While doing this, the quiet sounds will also decrease in volume, and you'll end up hearing only the loud sound.

When the loud sound then has finished played, the volume can be smoothly increased to the original level, allowing the quiet sounds to be heard once again.

My guess is that it's a little bit more to it than that. All sound effect are probably the same gain originally, but with some added HDR data to modify the gain of the original samples when played ingame.

But in the end, yes, it's probably a fancier name for automatic gain control as HDR lighting is a fancier name for automatic tone mapping.

I'm creating something similar, here is my simple demo:
http://www.gamedev.net/community/forums/topic.asp?topic_id=507340.