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Another feature, indicated by the appearance of “Gated” next to each band, is the limiter “
Hold”
function.
During brief pauses in limiter activity, the bargraphs “freeze” to show the limiter has entered the
Hold
function
of the algorithm; akin to the
Gate
function in the AGCs. This is most easily noticed when there is a “dry” voice
being processed. The Limiter bargraphs, like the AGC section, can indicate up to 25 dB of linear gain reduction.
Interpreting Processing Displays
Through observation of the processing bargraphs, significant information can be acquired and analyzed about
the audio signal on a moment-by-moment basis.
Since Omnia-3 is capable of performing many different processing functions at different times, the display
bargraphs may indicate various kinds of operation. This is based upon dynamic range differences in the
program material. For program material that is already processed or lacking dynamic range, this will cause the
bargraphs to indicate differently than material that possesses a high degree of dynamic range. This is because
audio signals that lack dynamic range, naturally or by previous processing, will possess a high level of RMS
energy and a low level of peak energy. Conversely, audio signals with wide dynamic range possess lower levels
of RMS energy but higher levels of peak energy.
Program material that has low dynamic range, high RMS and low peak levels will generate more activity in the
AGC sections and less activity in the Limiter sections in the displays. This is due to the AGC section
responding to the RMS energy while the Limiter section reacts to peak energy. When these situations occur, it is
normal for the unit to indicate more AGC action as compared to Limiter action. Sometimes the Limiter section
may not indicate any action! Examples might include heavily processed commercials or music, or music with
passages of sustained level. A good example is the Aerosmith CD “Pump.” This recording has very little
dynamic range. Try any up-tempo selection from this disk and you will see the Wideband-AGC section make
initial adjustments along with small amounts of limiting. Once adjusted, the Wideband-AGC section will be
deep in gain reduction, although with little movement, and limiting action will be minimal.
When the programming has wide dynamic range, with low RMS but high peak levels, the opposite will occur.
The Limiter section becomes active, while the AGC section will appear not to respond. During these situations
it is possible that the Limiter sections could approach full scale, while the AGC section may only indicate half
scale. Examples are: vocal passages or live voice, classical music, or passages with transient levels. Good test
examples: almost anything classical; almost anything by Steely Dan!
Also keep in mind that the AGC section will operate much more slowly than the Limiter sections. This is in part
due to the nature of each function. Remember, the AGC section operates on the RMS energy, which is
calculated over an “integration” time by the signal processor. It is during the integration time that the “average”
level is established, and gain adjustments, if needed, are made. This is why the AGC section will move slower,
since they are making changes, as needed, over relatively long time periods.
With the Limiter sections, the intention is to control the peak activity. This is accomplished by controlling, or
limiting, the highest crest, or peak, of the audio waveform. There is intrinsically little time available to get this
job done. The Limiter section must quickly grab the signal, reduce the gain to the proper operating range, and
then return the gain to normal until the next peak signal comes along. Peak energy must be detected and
adjusted in a quick and accurate manner while, at the same time, not interfering with the sonic integrity of the
audio signal. For this reason, the Limiter sections operate very quickly, and on an as-needed basis.
Since these displays are capable of providing a wide range of information, we do not recommend setting up this
system to any specified amount of processing based upon meter indications. Instead, we recommend setting up
the processing by using your ears to judge the sound. We provide the meters to analyze the signals and aid you
on adjusting the specific parameters needed to achieve the desired sonic results.
