2 5
S
TEREO
O
PERATION
Compressing a two-channel (stereo) signal with two independent compres-
sors creates a problems: if one channel is compressed more than the other,
the stereo image will shift to one side, causing an imbalance in the perceived
stereo sound field. To prevent shifting, DOD has incorporated a Stereo Link
switch on the 866. This switch allows both channels to track in perfect uni-
son while the detectors for each channel operate independently. When the
Link switch is depressed, the detectors are tied together and both channels
react to the higher of the two channel signals. This eliminates channel over-
ride, and the stereo image is preserved.
S
PECIAL
A
PPLICATIONS
The uses for a compressor don't end with compression and protective limit-
ing. Applications such as "ducking", "de-essing", and "de-thumping" can be
achieved with equal ease, and their uses are many.
The 866 provides Side Chain Inputs and Outputs, which allow direct access to
each channel's detector circuits. Since the detectors control the compressing
VCA (voltage-controlled amplifier), one can control the program material with
a completely unrelated signal. This is done by inserting the control signal into
the Side Chain Input.
Ducking is a good example of this type of application. Ducking is simply gain
reduction of a signal when another is present. This technique is widely used
in sports broadcasting to reduce the level of the crowd background signal
when the announcer is speaking. The preamplified voice of the announcer is
sent to a side chain input to compress the noise of the crowd. The voice and
crowd signals are then mixed together. For this type of application, the com-
pression ratio is kept fairly low with long attack and release times.
The Side Chain output is provided so that the controlling signal (not the pro-
gram material) may be modified before reaching the detectors.
The most common use of this technique is for de-essing. A de-esser reduces
the high frequency sibilance in the "s"s and "t"s of speech to prevent tape sat-
uration or high frequency driver damage. Connect the Side Chain Output to
an equalizer whose output is connected to the Side Chain Input of the 866.
The areas where most of the "ess" energy is located are between 2.5 kHz and
10 kHz. If these areas are boosted on the equalizer, the gain of the program
material will be reduced more by the compressor because of the excess gain
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