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Operators Manual
What is required is a device that can monitor the signal passed to it, and allow the
average level
to pass untouched. At a
threshold level
the device will begin to turn
down the level by a certain amount. This
amount
can be varied, to offer more or less
attenuation of signals above the threshold. What would also be useful would be some
way of controlling the
rate
at which the level is turned down (slower rates will not
sound as unnatural as the effect of ‘reaching for the volume control and giving it a
sharp twist’). Additionally, the ability to change the
rate of recovery
of the original gain
over a period is as important.
How does a Compressor work?
This is, in essence, exactly what a compressor does. Consider the diagram below,
which shows a signal level versus time . It represents a burst of audio, which is
initially below the threshold of the compressor - in region 1. As this is in the ‘safe’
region, it is unaffected by the compressor. It can be thought of as the average signal
level and remains unattenuated. However, in region 2, the signal has risen (very
sharply, hence the sudden jump) to a level above the threshold.
This signal is potentially
too high and must be
reduced in level to a
more acceptable value.
The difference
between the original
signal and the
compressed signal is set
by the Ratio. So, for
example, consider the
input jumping from 0dB
to +10dB, with the
threshold set to 0dB.
If the output rose by
5dB, then the ratio would be 10/5 or 2:1. Comparing the level displayed on the input
meter with the level on the output meter (assuming all other dynamics modules are
bypassed) will demonstrate the level of Gain Reduction being applied to any signals
that exceed the threshold. This amount is shown on the Gain Reduction meter for
the compressor.
Overleaf is the same signal after passing through the compressor. Important in region
2 is the red shaded area – this represents the time to fully apply the gain reduction set
with the ration control, or the Attack time.. The faster the attack time, the less signal
will ‘escape’ through the compressor before it reacts and applies gain reduction. The
setting of this control will be discussed in the next section. It’s value can have a
profound effect on the transparency of the compressor – that is, how natural it
sounds and how noticeable its action appears.
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