Introduction; Technical Background - Behringer DSP1100 User Manual

1. INTRODUCTION

With the FEEDBACK DESTROYER you purchased a highly useful device for the control of sound reinforce-
ment systems, which will enable you to focus your attention on what is essential: your music. The fully
featured FEEDBACK DESTROYER not only suppresses feedback but also incorporates a wealth of addi-
tional functions in one single unit. Its 24 separate filters can be edited in all parameters and automatically
detect and suppress feedback frequencies. With its pro-level internal signal processing circuitry, the unit can
also be used as a high-end equalizer for stage and studio applications. The MIDI interface allows for integrat-
ing the FEEDBACK DESTROYER into any MIDI system, and the open system architecture enables you to
update the system software whenever you want. In a word: the Behringer FEEDBACK DESTROYER was
built for the next millennium.

1.1 Technical background

The steady development of modern sound reinforcement systems has made it possible to produce almost
any level of loudness. Yet, the increase in loudness goes in line with a need for optimized audio quality.
Today, audiences expect to hear a powerful and transparent sound. Nothing can spoil a live event more than
interference and feedback.
High volume levels and the use of ever sophisticated monitor systems with a great number of speaker boxes
have increased the potential risk of feedback loops. Up to now sound engineers have used conventional 1/3-
octave equalizers to suppress unwanted feedback. Now, the Behringer FEEDBACK DESTROYER gives
you the option to delegate this task to the FEEDBACK DESTROYER, so that you can pay your music your
undivided attention instead of having to suppress feedback with graphic EQ's using a trial-and-error ap-
proach.
To fully understand how the Behringer FEEDBACK DESTROYER works you will need to know the meaning
of a few fundamental terms used in signal equalization, such as:
dB, decibel
quality factor (Q), bandwidth
octave, 1/3-octave
With the FEEDBACK DESTROYER, as with any other type of equalizer, the amount of boost/attenuation
applied to a specific frequency is expressed in decibels (dB). What's a decibel? The abbreviation dB is not a
unit (although often used as one), but describes a logarithmic proportion. The entire dynamic range of human
hearing (from the threshold of audibility to a jet-airplane, see fig. 1.1) starts with about 0.00002 Pa (threshold
of audibility) and goes up to 113 Pa (threshold of pain).
The range of sound pressure levels or the dynamic range of human hearing encompasses seven times the
power of ten, which corresponds to a factor of 10,000,000. This enormous range of values is difficult to
handle and additionally does not represent the subjective perception of sound, since human hearing tends to
use a logarithmic curve. When an increase in loudness by the factor two is perceived as one step, four times
the loudness level equals two steps. So, the decibel is a unit of measurement that describes a level in relation
to a reference quantity. To make clear which reference quantity is meant, the abbreviation SPL (sound
pressure level) is sometimes used together with dB. Starting with a value of 0 dB SPL for the threshold of
audibility, any dB values can be calculated by means of the following formula:
whereas L = e.g. the absolute sound pressure level in dB SPL, U
0.00002 Pa, U = e.g. the sound pressure (in Pa) produced by the sound source to be calculated, and log =
2
decimal logarithm.
U
2
L 20 log
U
1
1. INTRODUCTION
= e.g. a reference sound pressure of
1
7