SPL 9945, User Manual

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14
Operation
Compressor/Limiter
Make Up
With the Make Up control the level reduction caused by compression or
limiting can be restored. With assistance of the Gain Reduction display in the
display field setting the Make Up control is very easy: If the maximal reduc-
tion value caused by the loudest tone amounts to -9 dB, for instance, the
Make Up control is also to be set to the value +9 dB. If the
Compressor/Limiter is now switched off the achieved gain in loudness will
be audible.
Technical Information regarding the Compressor/Limiter
In the Compressor/Limiter section of the Channel One the parameters for
the time constants (Attack and Release) are set automatically and adapt
themselves to the changing conditions of the input signal, far better than
can ever be achieved by manual adjustments. The transient and final oscilla-
tion behavior of voices and instruments are constantly changing and at
times are so erratic that a manual control will only achieve good average
values, which at critical moments can produce disadvantageous effects
(distortion and artifacts).
If for example the compressor has to react very quickly to harsh P or T
noises it must also be capable of reacting slowly to softer tones – otherwise
distortion occurs. Accordingly the Channel One Compressor/Limiter regu-
lates the level of large fluctuations faster than smaller ones; tones of longer
duration are automatically processed with a longer attack time to prevent
distortions.
Even the control of the release time is dependent on the input signal. Fast
and large level fluctuations are correspondingly processed with shorter time
constants than minor fluctuations in order to limit the distortion of the
audio signal as far as possible. Overall this technique provides the optimal
solution between fast, unobtrusive control response and the least distortion
of the audio signal. The result is a natural and transparent sound impression.
A further technical specialty of the circuitry contributes to the high audio
quality of the Compressor/Limiter in the Channel One: the Double-VCA-
Drive®. Two That 2181 VCAs are utilized, one receives the in-phase, the other
the out- of-phase signal. Subsequently the signal is passed through a diffe-
rential amplifier. The effect of this circuitry is that distortion products and
offset fluctuations are removed. The product of the differential of both
signals (simply stated) means that possible interference is canceled out. The
original information is however further amplified by 6 dB. In addition the
VCAs provide relief to each other because they share their loads.They do not
run the danger of operating in the saturation range – this would lead to
offset noises, audible as clicks or pops.
The Double-VCA-Drive® circuitry overall displays vastly improved distor-
tion values so that a distinctly clearer and more transparent sound impres-
sion is achieved than with conventional circuitry. Voices and instruments are
given a considerably more natural and dynamic timbre whereas ”muffled”
tones are not audible.
The Compressor/Limiter characteristics are portrayed on page 24.
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