Appendix B
Audio Processing FAQ…
While Chapter 5 was written with the idea to aid in making processing adjustments, we’re still aware that there are
other processing configurations that some users desire. The following is a list of Frequently Asked Questions
compiled from our Omnia Customer Support database:
1. How do I eliminate some softer passages on older recordings from sounding dull?
This is easily done by reducing the
GATE
thresholds in the
HF
(Band-4) and the
SHF
(Band-5) sections of the
Multiband AGC. Set these gate levels to a value of “1” and this will allow those bands to increase gain in this
part of the spectrum when there is low level of presence or high frequencies of older recordings. The only
caveat is that this change may increase high frequency noise or hiss.
2. What is the difference between running the AGC Release times fast, as compared to doing the same thing in
the Limiter bands?
The first thing to understand is that the AGC and Limiter sections are designed to perform two totally different
operations. The AGC section is working on the controlling the medium-term
average
level, whereas the
Limiters are more concerned with the short-term
peak
levels. There’s a reason for this, as well as why the AGC
sections feed the limiter sections. To try and paint the picture, let’s think of a funnel turned sideways, so that the
wide end of the funnel is on the left side, and the narrow end is on the right. Now, let’s feed wide dynamic
range audio into that funnel.
As the audio is funneled down to a smaller dynamic range, different styles of processing are used to perform
this. The AGC section is part of the initial funneling process, and it will be working on controlling the medium-
term
average
, or the meatier part of the signal. Some folks refer to this as the RMS level. After initially
funneling down the audio level, the next stage is the limiting section where the remaining short-term peaks are
controlled. The last stage is the clipper, where any remaining uncontrolled signals are processed in a very
aggressive manner. But in our discussion, we’re only concerning ourselves with the AGC and Limiter sections.
When the release time function in the AGC section is set faster, it will yield increased audio density to the
following limiter section. This will build up perceived loudness, but it will be done in a more graceful manner.
The audio will appear “fuller”. This is a good section to adjust first when trying to build a bit more on-air
density.
The release function in the Limiters, will do a bit of the same, but its side-effects are a bit more audible.
Because the action of the limiters is generally faster than the AGC sections to begin with and the compression
ratio is higher, an increase in release time will also raise the level of Intermodulation (IMD) distortion. This is
why Omnia-6EX has AGC algorithms that are designed to carry quite a bit of the load for loudness processing.
You can always drive the limiters harder if you wish, but it will be at the expense of that added
busy
sound due
to the harder work that the limiters are doing.
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