Stereo is two wave files in one track. 5.1, when Vegas project settings are set to 5.1, and you drop a 5.1 video file on the time line, you get the one video track and three stereo audio tracks, one for front left and right, one for rear left and right and one for center and sub. An audio buss is a track usually used as an effect buss, where you can add a reverb for instance and send any desired amount from any audio tracks to it and it’s output normally goes to the master out. This method is used to get an effect on many tracks with only one effect used. You can use a buss for like a master level for drums for an example. You you could set the output of all the drum tracks to a buss, set all vocal outputs to another, and be able to turn all the drumes up or down with one fadre, same with the vocals. These are audio busses. Audio bass it the low frequency of an audio signal. Hope this helps. Danny Hays