Wheatstone Corporation WheatNet-IP BLADE3, Техническое руководство

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A U R A 1 I P P R O G U I
WheatNet-IP BLADE 3 / Jan 2016
Makeup Gain
All of Aura1ip’s processing is accomplished by feed-forward control algorithms.
Feed-forward control has the advantage that it doesn’t rely on errors in
the compressor’s output signals (as do feed-back algorithms) in order
to dynamically control the gain. Rather than measuring mistakes in
the output level and then trying to correct them by a (now very late)
control signal, feed-forward control prevents errors in the output signal
by carefully measuring changes in the input signal’s levels and then
calculating the precise amount of gain control needed to achieve the
perfect output.
Because the compressor’s output levels are controlled by changes in the input levels,
when the input levels go up, the compressor will push the output level down by whatever
amount of gain reduction is called for. This causes the output levels of feed-forward
compressors to need to be “made up” after processing, and this is accomplished with a
control called Makeup Gain.
The amount of Makeup Gain needed is a function of how much gain reduction was
called for due to an increase in input level. In our design we leave around 6dB of additional
headroom to accommodate the compressor attack times and such, so if 20dB of gain
reduction is being done by a band’s AGC/Compressor, then the correct amount of Makeup
Gain will be 20dB plus that 6dB, or 26dB.
The less gain reduction being called for, the less Makeup Gain that is required to bring
the signal back up to normal levels afterwards.
Those who may be concerned about “… adding gain after AGC/Compression because
it will increase noise…” need to know that the signal processing chain inside Aura1ip has
144dB of dynamic range. This is approximately 50dB more dynamic range than a digital
CD. Therefore “noise” is of no concern whatsoever – the processing chain will remain
absolutely dead quiet regardless of the amount of Makeup Gain that may be required.
Note also that the amount of Makeup Gain is somewhat dependent on the Compression
Ratios being applied to the signals in each processing band. The higher the Compression
Ratio, the tighter the output level is regulated, and therefore the more Makeup Gain that
will be required. However, the difference in the Makeup Gain required with 20dB of
compression at a 4:1 ratio and that required at 20dB compression with a 10:1 ratio is only
around 3dB.