BBE 422A corrects the phase and amplitude relationship on the harmonic and fundamental frequencies which is called " envelope distortion". The loss of sound integrity is perceived as muddy and smeared. To correct problems BBE applies phase correction to the high frequencies. Furthemore the signal is broken up into three sub-bands. The low grouip is delayed about 2.5 ms by a low pass filter. the mid drop is delayed about 0.5 ms and passes through an active band-pass filter. The high frequencies are used as a point of reference.to make dynamic amplitude corrections to the high frequencies. 

      Two RMS average loudness detectors continuously monitor the both the mid-range and the high-frequencies to compare the relative harmony content levels of the two bands.