dod DOD 866 Series II DOD 866 SERIES II GATED COMPRESSOR:LIMITER

DOD

SIGNAL PROCESSORS

866 SERIES II GATED

COMPRESSOR/LIMITER

OWNER'S MANUAL

866 SERIES II GATED

COMPRESSOR/LIMITER

INTRODUCTION :

The DOD 866 Series II is a stereo gated compressor/limiter that can be operated as two
independent compressor / limiters or as a single stereo unit. The 866 Series II incorporates
"soft knee" characteristics in its compression action to yield natural sound under gain
reduction conditions.
Also featured on the 866 is a noise gate to ensure quiet operation when signal is not
present. All critical operating parameters are adjustable, allowing maximum flexibility over
a wide range of applications.
However you choose to use it, the 866 has been
designed to be an affordable audio tool for the musician, performing group, and small to
medium-size recording studio.

INSTALLATION :

Install the 866 in a rack using the provided rack screws. Route the power cordaway from
audio lines and plug into a convenient outlet. Connect audio lines to the appropriate
channel A and B jacks on the compressor.

FOR BALANCED CONNECTION:
Use 1/4" tip-ring-sleeve phone plugs, wired as follows:
tip: high

ring: low
sleeve: ground

FOR UNBALANCED CONNECTION:
Use either 1/4" mono phone plugs or RCA phono plugs, wired as follows:
tip: hot

sleeve: low

CONTROLS AND FUNCTIONS :

Gate Threshold:

The Gate Threshold controls the level at which the 866 will allow the input signal through
to the compressor section of the unit. If the signal level is below the threshold, no signal is
allowed to pass. The red LED will light whenever the signal is being gated. To disable the
gating action, set the Gate Threshold control to the full counter-clockwise position (the
gate control is fully independent of all other controls on the 866).

Input Gain:

The Input Gain control allows you to adjust the signal level to the compressor. This control
directly affects the setting of the Gate Threshold control and the Compressor Threshold
control, and is active even when the Compress switch is in the out position. With the Input
Gain control set to 0 dB, over 20 dB of headroom is available to the compressor.

Compressor Threshold:

This control sets the level at which the compressor begins to act. The Input Gain control
affects the Compressor Threshold setting by changing the overall level that the
compressor sees. When used in combination with the Input Gain control, the Compressor
Threshold control can be adjusted to accommodate a wide range of signal levels.

Ratio:

Determines the amount, or ratio, of compression applied to the incoming signal. A ratio of
1:1 means that no compression is applied; a ratio of less than 10:1 is generally considered
compression; a ratio of more than 10:1 is generally considered limiting; a ratio of °:1 allows
no signal above the Compressor Threshold level setting.

Attack:

This control adjusts the speed with which the compressor reacts to an increase in input
signal level above the threshold. Shorter attack time settings will cause the compressor to
react more quickly to transients, giving an added measure of protection to sensitive
equipment. Longer attack times allow more of the transient to pass, yielding a more natural
sound while still compressing the dynamic range of the signal.

Release:

The Release control adjusts the speed with which the compressor reacts to a decrease in
input signal level above the threshold. Faster release time settings can cause a sudden
increase in noise on peaks for some program material as the compressor lets go. This
effects is known as "breathing". Increasing the Release time setting will help minimize
breathing.

Output Gain:

Determines the output level of the compressor. This is useful when making up for gain lost
in the compression process. The output level is active only when the Compress switch is
depressed.

Gain Reduction:

This six segment LED bar graph indicates the amount of gain reduction by the
compressor. It operates even when the Compress switch is in the out position so that the
user can preview the action of the 866 before it is inserted into the signal path.

Compress:

The compress switch activates the compressor when depressed.

Stereo Link:

Depressing the Stereo Link switch links the two compressor channels for stereo operation.
In stereo mode, the compressor will react to either channel, while reducing gain in both
channels. Both channels of the 866 are identical in control and function EXCEPT when
placed in the stereo mode. In stereo mode, the channel 1 controls become the master
controls for both channels, while the Input Gain controls remain independent for each
channel.

INPUTS AND OUTPUTS :

The rear panel inputs and outputs and their functions are as follows:

Input:

The inputs of the 866 will accept line level signals, either balanced or unbalanced. A 1/4"
tip-ring-sleeve phone jack and an RCA phono jack are provided for each input. Using the
1/4" input jack disconnects the RCA input jack.

Output:

The outputs of the 866 will drive either balanced or unbalanced lines. A 1/4" tip-ring-sleeve
phone jack and an RCA phono jack are provided for each output. Both the 1/4" phone
jacks and the RCA jacks may be used at the same time.

Side Chain Input:

Allows access to the signal detector circuit of the compressor, permitting control of the
compressor with another signal for such applications as "ducking". When used with the
Side Chain Output, the original input signal can be modified for applications such as "de­essing". Inserting a plug into this jack opens the internal side chain path so that the
detector will only respond to the signal at this jack. In the stereo mode, both channels of
the compressor react as one.

Side Chain Output:

The Side Chain Output is the buffered output normally fed to the detector. It is used in
conjunction with the Side Chain Input to modify the detector signal for special applications
such as "ducking" and "de-essing". For these applications, the Side Chain Output signal is
sent to a signal processor and returned through the Side Chain Input.

APPLICATIONS

The flexibility of the 866 allows it to perform many signal processing tasks with

equal ease and clarity. Here are a few concepts necessary to understand before using the

866.
Two of the most common applications for the 866 are simple compression and limiting.
Compression and limiting are performed in a similar manner, with two important
differences: the Compressor Threshold level and the ratio settings for compression are
usually much lower than for limiting.

The Compressor Threshold controls the point above which the compressor begins
to reduce the gain. For compression, the Compressor Threshold is set low, so that even
low level signal will activate the compression. For limiting, the Compressor Threshold is
set high so that all of the dynamics of the signal are preserved, but extremely high levels
are reduced to protect amplifiers, speakers, or to prevent tape saturation. In this
application, the detector ignores signal level changes below the threshold.

The 866 features a "soft knee" compression curve for more natural sounding
compression. This means that as the signal level approaches the threshold setting, the
compressor starts to react. The ratio, or slope, of the gain reduction continues to increase
gradually as the signal passes above the threshold until it reaches the final gain slope set
by the Ratio control. This feature makes the compressor's operation less obtursive by
easing into full compression.

As you increase the compression Ratio, the "knee" gets sharper, and the gain
reduction increases more rapidly with increased signal. Protective limiting requires a high
compression Ratio setting, so that full compression is reached quickly.
The time it takes for the detector to react to an increase in signal level is determined by the
Attack control setting. To preserve some of the transient punch of a signal, the Attack time
should be set fairly high. This allows the user to compress the overall dynamic range of a
signal while still preserving the natural, open feel of the sound. For limiting, the Attack time
should be short, so that potentially damaging transients don't get past the limiting
protection of the compressor.

Release time is the opposite of attack time. The Release time setting determines
the amount of time the detector takes to react to a decrease in signal level and to release
the action of the compression. Faster release times will help preserve the original
dynamics of the signal, but may cause a problem in some program material. This effect is
called "pumping" or "breathing" . As the compressor lets go of the signal, the level of the
signal (and the noise floor) is allowed to rise. When the next transient hits, the signal level
is pushed down again according to the Attack time setting. Breathing can be minimized
using longer Release times, which smooth out the action of the compressor.

Once a signal has crossed the threshold, the compressor must be told how much to
reduce the gain. The Ratio control determines the amount of gain reduction, expressed as
a ratio, adjustable from 1:1 (no gain reduction) to °:1 (the signal is not allowed to rise
above the Threshold level).

Compression ratios express the ratio between the input signal level and the desired
outputlevel. A compression ratio of 2:1 means that for an increase of 2dB above the
threshold input signal, the compressor output will rise only 1 dB. At a ratio of 5:1, an input
increase of 5dB above the threshold will yield an output increase of 1 dB, and so forth. The
setting of the Ratio control is dependent upon the application in which the compressor is to
be used.

Hiss and signal processor idling noise are common sound reinforcement problems.
The more signal processors there are in line with the program material, the more noise is
produced at the final output stage. For this reason DOD has incorporated a noise gate in
the 866. A gate acts like a compressor in reverse. When a signal crosses the gate
threshold, it is allowed to pass unaffected. When the signal level falls below the gate
threshold level, the signal gain is attenuated, effectively shutting it off. The Gate Threshold
control of the 866 allows the user to adjust the threshold level of the noise gate. When the
control is in the fully counter clockwise position, the noise gate is inactive and all signals
will pass through. The Output Gain control allows the user to make up for gain lost in the
compression process and to set the output level of the compressor for compatibility with
other equipment.

SETTINGS :

Here are a few compressor settings that can serve as a starting point for the
applications covered up to this point:

Vocal Compression:

Compressor Threshold: low
Ratio: 5:1
Attack: 10 msec
Release: 200 msec

Guitar Compression for Extra Sustain:

Compressor Threshold: low
Ratio: 15:1
Attack: .5 msec
Release: 500 msec

Protective Limiting:

Compressor Threshold: high
Ratio: °:1
Attack: 0.1 msec
Release: 90 msec
For more information on compressors and applications, consult the Yamaha
Sound Reinforcement Handbook (Hal Leonard Publishing, #HL 00500964).
This book is an invaluable tool for beginners and veterans alike, and contains
a wealth of information on sound reinforcement theory and practical application.

STEREO OPERATION :

Compressing a two-channel (stereo) signal with two independent compressors 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 unison 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 override, and the
stereo image is preserved.

SPECIAL APPLICATIONS :

The uses for a compressor don't end with compression and protective limiting.
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 (voltage­controlled 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 compression ratio is kept fairly low with long attack and
release times.

The Side Chain output is provided so that the controlling signal (not the program
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 saturation 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 in that frequency range, thus
reducing the sibilance of the program material.
Attack and Release times should be set fairly short, and the compression ratio
should be below 8:1.

S PECIFICATIONS :

Frequency Response: 10 Hz - 30 kHz, ±0.5 dB.
THD+Noise: 0.06%.
Signal-To-Noise Ratio: -97 dB.
Input Impedance: 20 K1/2 unbalanced, 40k1/2 balanced.
Maximum Input Level: +21 dBu (ref.:0.775 Vrms).
Output Impedance: 511/2 unbalanced, 1021/2 balanced.
Maximum Output Level: +21 dBu (ref.: 0.775 Vrms).
Side Chain Input Impedance: 10 k1/2.
Side Chain Maximum Input Level: +21 dBu (ref.: 0.775 rms).
Side Chain Output Impedance: 511/2 unbalanced, 1021/2 balanced.
Side Chain Maximum Output Level: +21 dBu (ref.: 0.775 Vrms).
Gate Threshold: Adjustable from -55 dBu to -10 dBu.