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Interpreting Processing Displays
Through observation of the processing bargraghs, significant information can be acquired and
analyzed about the audio signal. Almost as if we were to take a moment by moment snapshot of
what is happening.
Since the Unity AM is capable of performing many different processing functions at different times,
the display bargraghs may indicate various levels 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 bargraghs to indicate differently than material that possesses a
high degree of dynamic range. What is meant by this? Consider the following. 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. Whereas audio signals with dynamic range possess lower levels of
RMS energy compared to higher levels of PEAK energy.
In relation to the processing displays on the Unity AM, program material that has low dynamic range,
high RMS and low PEAK levels, will create more action on the LEVELER sections and less activity
on the LIMITER sections. This is because the LEVELER section responds to RMS energy, and the
LIMITER section reacts to PEAK energy. When these situations occur, it is normal for the unit to
indicate more LEVELER action compared to LIMITER action. Sometimes the LIMITER section may
not indicate any action! Examples might be: heavily processed commercials or music. Music with
passages of sustained level. A good test example is the AEROSMITH CD “PUMP”. This record has
very little dynamic range. Try any up tempo selection from this disk and you will see the LEVELER
sections make initial adjustments along with small amounts of limiting. Once adjusted, the
LEVELER sections will basically not move and limiting action will almost be non-existent.
When the signal is has high dynamic range, low RMS and high PEAK levels, the opposite will occur.
The LIMITER section will become very active, while the LEVELER section will respond much less.
During these situations it is possible that the LIMITER sections could approach full scale while the
LEVELER sections 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 Steely Dan!
Also keep in mind, that the LEVELER sections will operate much slower that the LIMITER sections.
This is in part due to the nature of each function. Remember the LEVELER sections operate on the
RMS energy. RMS level is calculated, over time, by the signal processor, this is known as the
integration time
. It is during the integration time that the “average” level is established, and then
processing adjustment, if needed, is applied. This is why the LEVELER sections will move slower,
since they are making changes, as needed, over time.
With the LIMITER sections, the story is a bit different. Here the intention is to control the PEAK
activity. This is accomplished by controlling, or limiting, the highest crest, or peak, of the signal
waveform. For signal processing there is not much time allowed to get this job done. When the
