Omnia -6EX / EXi Installation And Operation Manual page 78

Omnia-6EX employs a Look Ahead limiter to provide absolute precision peak control for the HD Digital Channel.
This limiter has been designed to minimize processing side-affects like IMD, which are usually associated with
limiters of this type. Using an innovative design that cancels intermodulation products before they develop allows
this limiter to sound extremely transparent. The limiting function is derived using numerous control signals that
monitor one another. Customer access is provided to these signals so that the texture of the sound of this limiter can
be altered to taste. (These parameters will be described soon!)
This type of peak controller is used instead of a clipper because it does not generate the same high levels of THD as
a Clipper does. THD causes added difficulties in a coded audio system because the harmonics generated from the
clipping action create added artifacts and workload in the encoder. These are especially annoying at high
frequencies.
On the other hand, while a Look Ahead limiter yields extremely low levels of THD, it will create some IMD
component, but this still allows the audio coder to operate with minimal sonic artifacts.
There are tradeoffs in how each of these peak controllers sound when they are set to produce added loudness. When
a clipper is pushed, the audio may appear edgier. This is from the added harmonic content. In contrast, the Look
Ahead limiter will appear busier, or dense as the action of the control signal may be heard, when more limiting is
applied.
Limiter Drive: Here is where the loudness versus quality is most evident! This limiter's adjustment range is +/-6 dB,
in 0.1dB steps. It is advisable to make minor changes, primarily as the 'loudness fine tuner'. Be careful; there is a lot
of available power here!
Silk Action: This control adjusts the texture of the limiter when it is handling significant mid and upper midrange
program material. Higher numbered settings (clockwise) soften (or silken) the sound of the limiting at higher
frequencies, with only a slight reduction in brightness on some material but can result in a "queasy" quasi-pumping
sound on some material. The sound of limiting low frequency material (<2Khz) is largely unaffected.
Speed: This control adjusts the speed of the peak control network, affecting the texture of the limited audio. Higher
numbered settings are faster and while louder, may create a busier sound with more intermodulation distortion.
Density: Within the limiter algorithm are multiple networks that perform the timing, or attack/release functions.
Density is a single parameter that modifies these networks with the goal of creating added perceived loudness. This
feature allows the timing networks to be altered, for more/less processing, but also maintaining a balance of the IMD
reducing functions. Higher numbered settings increase loudness at the expense of distortion.
HF Shelf EQ: Depending upon how the processing is set for the conventional FM signal, there may be a need to
add or remove some high frequency spectra to the final mix if there is a desire to more closely match the sound of
the Look Ahead limiter to the pre-emphasized effect that the conventional FM channel processing possesses. It is
recommended that this parameter be left at 0.0dB to start with, and only adjusted after careful comparison to the
conventional channel.
Bandlimiting: Omnia-6.HDFM is capable of delivering 20kHz audio response to the HD Radio/DAB encoder. If
there is a desire to reduce the audio bandwidth, it is possible to reduce the spectrum in 2kHz increments from 20kHz
down to 12kHz. All of the filters employed for this function are phase linear.
Omnia-6ex Use and Operation Manual – V: 1.20
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