Biamp LTR - Manual (Page 174)

Nexia Manual LTR
Proper Gain Structure
Proper gain structure is important because it affects signal-to-noise performance and available
headroom within a sound system. Every sound system has some inherent noise, whether it be
self-generated by the internal electronics or induced into the signal path by external sources.
Therefore, unnecessarily low gain settings can result in signal levels which are significantly closer
to the noise floor, potentially causing a sound system to appear noisy. Conversely, excessive
gain settings may cause the audio signal to overdrive the electronics, resulting in severe
distortion due to clipping of the audio waveform. Besides being audibly undesirable, a distorted
waveform can also cause damage to some system components, such as loudspeakers.
In addition to its influence on signal-to-noise and available headroom, gain structure can affect
other aspects of sound system behavior. In particular, some audio components rely on signal
strength as part of their normal operation. These components may not perform as expected if
they receive signals that are lower, or higher, or even just different from what is anticipated.
Examples of such components are: Auto Mixers, Duckers, Levelers, Comp/Limiters, Ambient
Noise Compensators (ANC), and Acoustic Echo Cancellers (AEC).
Auto Mixer, Ducker, Leveler, and Comp/Limiter functions are triggered by input signals that
exceed a specified threshold. With Levelers and Comp/Limiters, signal levels below threshold are
not considered unusual (they simply are not affected by the component). However, Auto Mixers
will not pass signals that are below threshold, and Duckers will not automatically attenuate
program signal if the sensing input signal is below threshold. Furthermore, signals containing a
large amount of background noise can falsely trigger these components, if the level is set too high
and/or the threshold is set too low. It should also be noted that any real-time control of signal
levels should not occur before these types of components. For example, control of individual Auto
Mixer channels should not take place ahead of the Auto Mixer. Instead, the Auto Mixer Input
Level controls (which are post-threshold) may be used for this purpose.
Ambient Noise Compensation (ANC) relies on a continuous and accurate model of the program
signal level, to differentiate it from changes in the ambient noise level. So, real-time control of
levels should not occur after this type of component. Acoustic Echo Cancellation (AEC) relies on
a continuous and accurate model of the signal to be cancelled from the microphones. So, any
real-time control of signal levels at the loudspeaker output should be duplicated for the AEC
Reference. If these signals are different, a 2-channel ‘ganged’ Level control may be used.
What is proper gain structure? Generally speaking, proper gain structure is establishing and
maintaining good signal strength throughout the entire sound system. In most cases, this means
that the relative volume of loudspeakers should ultimately be determined by adjustment of the
power amplifiers (after prior system gain settings have been established). Other system outputs
(such as recording feeds) may require lower levels, which should be established by selecting an
appropriate reference level at the output itself. Other than real-time level control (as described
previously), signal attenuation within the system should be avoided.
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