BBE 822A - Page 3

Congratulations
Thank you for buying the BBE Model 822A Audio Processor. You now own a very unique signal processing device with
no other equal in the audio world today. Whether you purchased the BBE 822A for recording studio, live concert, playback
or industrial use, you will find the unit's rugged construction and careful electronic design a welcome addition to your audio
system.
This manual will help you use the BBE 822A more effectively and in ways of which you may not be aware. Review of
the information contained in this owner’s manual will answer most of the common questions that our service department
receives. But if you have a question, please feel free to call toll-free (US) 800-233-8346 or (CA) 800-558-3963.
The BBE ™ Process~"What Is It?”
Loudspeakers have difficulty dealing with the electronic signals supplied by an amplifier. These difficulties cause such major
phase and amplitude distortion that the sound reproduced by a speaker differs significantly from the sound produced by the
original source.
In the past, these problems have proved unsolvable and were thus relegated to a position of secondary importance in audio
system design. However, phase and amplitude integrity is essential to accurate sound reproduction. Research shows that the
information which the listener translates into the recognizable characteristics of a live performance are intimately tied into the com¬
plex time and amplitude relationships between the fundamental and harmonic components of a given musical note or sound.
These relationships define a sound’s “sound.”
When these complex relationships pass through a speaker, the proper order is lost. The higher frequencies are delayed. A
lower order frequency may reach the listener’s ear first or perhaps simultaneously with that of a higher frequency. In some cases,
the fundamental components may be so time-shifted that they can reach the listener’s ear ahead of some or all the harmonic
components.
This change in the phase and amplitude relationship of the harmonic and fundamental frequencies is technically called “enve¬
lope distortion.” The listener perceives this loss of sound integrity in the reproduced sound as “muddy” and “smeared.” In the
extreme, it can become difficult to tell the difference among musical instruments, for example, an oboe and a clarinet.
BBE Sound. Inc. conducted extensive studies of numerous speaker systems over a ten year period. With this knowledge it
became possible to develop an ideal speaker and to distill the corrections necessary to return the fundamental and harmonic
frequency structures to their correct order. While there are differences among various speaker designs in the magnitude of their
needs for correction, the overall pattern of correction needed is remarkably consistent.
The BBE ™ process is so unique that 42 patents have been awarded by the U.S. Patent Office.
»How It Works”
The BBE process imparts a pre-determined phase correction to the high frequencies where most harmonic information
exists. This is done by breaking the signal into three sub-bands or groups; the low frequency group which is crossed over
at 150Hz, the mid-range group which is crossed over at 1200Hz and the high frequency group that handles everything
else up to 20kHz.
The low group is delayed about 2.5 ms (milliseconds) via group delay within a passive low pass filter. The front panel
control allows for either a flat response, reduction or boost of the lows at 50Hz.
The mid-range group is delayed only about 0.5 ms and passes through an active band pass filter. The mid group is used
as a point of reference to make dynamic amplitude corrections in both positive and negative directions to the high frequency
group which has been passed through a high quality VGA (Voltage Controlled Amplifier).
Two RMS average loudness detectors continuously monitor both the mid-range and high frequencies to compare the
relative harmonic content levels of the two bands and apply the appropriate amount of control voltage to the VGA , thereby
determining the amount of high frequency harmonic content present at the final output of the BBE processor.