5
Operating Controls
Input/Output Meter Switch
- This switch selects the signal for metering by the INPUT/OUTPUT LEVEL METER.
The switch lights indicating the input signal is currently being sent to the meter. When the switch is in the out
position, the output signal is selected for metering, and the switch will not be illuminated.
Output Gain Control
- This control sets the output gain of the compressor. It can be continuously adjusted
between -20 dB and +20 dB. Use this control to compensate for signal level loss due to compression and to
adjust the nominal output level of the unit.
Bypass Switch
- This switch bypasses the unit completely, “hard-wiring” the input directly to the output, and
the signal is not processed in any way. The switch will light indicating that the unit is currently bypassed.
PeakStopPlus™ Level Control
- This control sets the level to which the output signal is reduced whenever
it exceeds this level. It can be adjusted b4 dBu and +22 dBu (OFF). This PeakStopPlus™ limiter
uses a propietary dbx two-stage limiting process. The first stage is the Instantaneous Transient Clamp™
which clamps the signal with a soft logarithmic clamp function. This logarithmic function assures that the
signal will not exceed the level set by the PeakStopPlus™ LEVEL control by more than 2 dB typically, and
that it will not introduce harsh artifacts. The second stage is a unique program limiter featuring Intelligent
Predictive Limiting™. Its function is to monitor the input signal and intelligently predict the amount of gain
reduction needed to keep the output signal below the ceiling set by the Instantaneous Transient Clamp™.
The PeakStopPlus™ limiter must come after the OUTPUT GAIN control. If the OUTPUT GAIN is set too high as
compared to the PeakStopPlus™ LEVEL control, continuous limiting can occur. While PeakStopPlus™ is typically
used as a protective function, creative effects can be achieved by intentionally driving the signal into heavy
PeakStopPlus™ limiting. Great care has gone into the design of the PeakStopPlus™ limiter to keep it acoustically
transparent. Appropriate use of it can protect your gear while keeping the signal free of artifacts.
PeakStopPlus™ Threshold (+) LED Indicator
- This LED illuminates when the output signal exceeds the level
set by the PeakStopPlus™ LEVEL control indicating that PeakStopPlus™ limiting is occurring.
Figure 3 illustrates the protective action of the PeakStopPlus™ limiter. The signal with the thin line weight
represents an unaltered input signal. As you can see, peaks of the input signal exceed the clamping level. The
signal with the heavier line weight represents the output signal. The peaks of the input signal which exceeded
the clamping level are not allowed to exceed this level at the output. This instantaneous protective action is
invaluable for driver protection in speaker systems and for digital recording where it is desirable to record as
“hot” as possible, while still avoiding the disastrous result of running out of headroom. Following this clamping
action, Intelligent Predictive Limiting™ takes over, typically within 5ms, as long as the input signal continues
to exceed the PeakStopPlus™ threshold. This program limiter quickly attenuates the input signal to a level
safely below the clamping level, typically 2 dB lower than the clamping level. The PeakStopPlus™ level control is
calibrated to this lower level, so if an absolute ceiling is required, set the level 2 to 3 dB below the front panel
setting.
The attack and release times of the Instantaneous Transient Clamp™ are zero, while the Intelligent Predictive
Limiting™ attack and release times are program-dependent. That is, for larger excursions over the threshold, the
attack time speeds up, and for smaller excursions over the threshold, the attack time slows down. Similarly, for
large excursions over the threshold which cause more PeakStopPlus™ gain reduction, the release time increases
and is roughly proportional to the amount of gain reduction that occurred.
