■ FIGURE 4.
Platform gain principle.
■ FIGURE 5. Diodes and other circuitry are added to the
resistor-capacitor time constant circuitry in a limiter to
produce the platform effect.
■ FIGURE 6. Circuit diagram for
the platform gain controller. The
voltage-controlled amplifier and
input-output buffers are shown.
pulls back from its peak at point C, the
output changes in a 1:1 correspondence
with the input, as it did before the
threshold was reached.
It's only when the input signal is
reduced quite a bit (at point D) that the
gain control kicks in to maintain the
output at a higher signal level. Finally, if
the input signal is reduced quite a bit, at
point E the output tracks the input. If
somewhere in between — from point A
to point B — the input level again
increases, it takes a
measured increase in the
input signal before the gain
control again kicks in to
The regions B-C and D-E are
the gain platforms, and the
signal level difference
between these two platforms
sets the dynamic range for
the controller. What all this
means is that the dynamic
range is preserved, while at
the same time peaks are
prohibited and average
volume is kept high. The
circuit effectively acts like a
careful engineer who turns
up the volume when the
signal is too low, and turns it
down when it gets too high.
■ FIGURE 7. Circuit diagram for the platform gain controller
(continued). The full wave rectifier and control voltage buffer are
shown. The platform network is contained within the dotted lines.
Some magic tricks are
done with mirrors. The