In THX parlance "reference level" means a couple of different things. The level calibration of the white noise generator for surround level is 85db for THX movie theaters. For Home THX, it is usually specified as 75db. Using your trusty Radio Shack analog SPL and your internal or external white noise generator, you set all your speaker levels to 75db. When people speak of playing a THX system at "reference level" that is the 0db setting on your controller after the levels have been calibrated. Movie dialog should be at about 75db and peak levels can be as high as 105db. Hope this helps.
