Omnia Audio Omnia F/XE - Manual (Page 42)

40 | Section 5
WB-AGC (WideBand AGC)
A flexible wideband leveler section provides smooth, transparent control of the input program. This is
achieved through two significant Omnia innovations, a dual referenced release gate and a hidden, intel-
ligent “makeup” gain algorithm. The dual gate reference is a unique process that correlates the dynamics of
the audio input signal to a “rolling” reference level, and from that information makes conditional decisions
affecting the character of the release function.
A hidden, make-up gain control signal determines when the amplitude of the input program suddenly falls
to a reduced level. It then adjusts the side chain gain in order to “fill in” the softer program passages so that
the average level is increased. This allows the AGC function to operate with slower time constants, while
significantly increasing the average audio level. These slower overall time constants yield lower intermodu-
lation distortion, contributing to Omnia’s trademark sound.
Using classical music for an example, the orchestra often plays forte, and then enters abruptly into a quiet
passage. Conventional AGC algorithms would hold the softer passage down until it was able to slowly
recover at the static release time setting, making such passages nearly inaudible at normal listening levels.
Omnia F/XE’s makeup gain function allows a hidden, faster time constant to provide quick recovery, but
only during the softer passage. As soon as the orchestra starts to play louder, the “makeup” time constant
yields control back to the primary AGC circuit, returning gain to the previous platform level. This sophisti-
cation preserves the dynamic integrity of the signal while greatly enhancing the listenability of the program.
This is the first processing section within the Omnia F/XE, so the controls in this section affect the overall
signal, its density, and hence affect every other processing section following it. The job of the Wideband
AGC is to erase long-term audio level fluctuations, while doing so in a very unobtrusive manner. This sub-
menu provides a few parameters that tailor the action of this section.
Drive
Drive sets the audio level which enters the WB-AGC. Increasing the Drive will produce more compression.
This control is calibrated between –6dB and +6dB, and adjusts the signal level into the Wideband AGC. It
should be adjusted to net approximately 12dB of gain reduction with typical programming. Too little gain
reduction can defeat the “leveling” function of the Wideband AGC. Too much gain reduction has little
additional benefit. Nominal gain reduction values for the Wideband AGC are between 10 and 15dB.
Release
Release controls the speed of recovery for any given amount of gain reduction. Faster action yields less
dynamic range and the presence of more density to the audio. The Release control sets the time constants in
relative terms using Slow, Medium, and Fast. Because the time constants are program-dependent, calibrat-
ing these controls in absolute time values (ms/dB) would be useless—therefore we use simple terminology.