Eventide Omnipressor 2830Au Manual
Eventide
Kompressor
Omnipressor 2830Au
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INSTRUCTION MANUAL
Eventide Inc
One Alsan Way
Little Ferry, NJ 07643 USA
1-201-641-1200
eventideaudio.com
Omnipressor Model 2830*Au User Manual
Version 1.0.0
P/N: 141392 Rev A
This User Manual is an updated version of the original Omnipressor
instruction manual from 1974. Like the unit itself, the manual remains
true to the original intent and application. References to tape machines,
phone lines, etc. appear throughout.
Eventide is a registered trademark of Eventide Inc.
Omnipressor® is a registered trademark of Eventide Inc.
© 2023 Eventide Inc. All rights reserved.
SECTION 1
General Description
Specifications
SECTION 2
Connection Instructions
Control and Indicator Description
Linking
Applications---Introduction
Application Notes
1. "Your Backwards Omnipressor"
2. Standard Operating Modes
3. Voltage Controlled Amplifier
4. Predictive Compression
5. Omnipressor As A Noise Reduction Unit
SECTION 3
Block Diagram
Theory of Operation
INTRODUCTION
CONNECTION AND OPERATION
TECHNICAL DATA
1
2
3
4
7
8
10
12
13
14
15
17
18
OMNIPRESSOR MODEL 2830*Au
TABLE OF CONTENTS
The 50th anniversary Model 2830*Au Omnipressor
® is a professional-quality dynamic
modifier, combining the characteristics of a compressor, expander, noise gate, and
limiter in one convenient package. Its dynamic reversal feature makes high-level
input signals lower than corresponding low-level inputs. Musically, this reverses
the attack-decay envelope of plucked strings, drums, and similar instruments and
gives the effect of “talking backward” when applied to a voice signal. When a return
to normalcy is desired, the LINE switch is used to bypass the Omnipressor.
The Omnipressor provides an unusually wide range of controls, useful in all pro-
gram-controlled gain changes. The continuously variable Expansion/Compression
control goes from an expansion range of 10 to 1 (gate) to a compression range of
−10:1 (abrupt reversal); attenuation and gain limit controls adjust the gain control
range from a full 60dB to as little as plus and minus 1dB; and variable time con-
stant controls adjust attack/decay times over an approximate 1000 to 1 ratio. The
unit’s bass-cut switch limits low-frequency response in the level detector.
The Omnipressor’s unique metering system employs a logarithmic amplifier to generate
information on Input, Output, and Gain. Some of the unusual capabilities of the unit
are illustrated on the graph below.
A: DYNAMIC REVERSAL An input level of +10
results in an output of −10. An input level
of −10 results in an output of +10.
B: GATE As the signal decreases below +10,
the device gain rapidly goes to minimum.
C: EXPANSION A 40dB input range results in a
60dB output range.
D: CONTROL CENTERED Input level equals
output level.
E: LIMITING Gain is unity until input is 0dB.
Above 0dB. A 30dB change in input produces
a 6dB output change. (Line is offset for clarity.)
F: INFINITE COMPRESSION Output level remains
unchanged regardless of input level.
OMNIPRESSOR CAPABILITIES
GENERAL DESCRIPTION
1
2
0 to +8dB nominal level. Threshold control provided to center
gain control operation over range of −25 to +15dB. Maximum level
should not exceed +20dB or clipping will occur.
600 ohm audio transformer.
0 to +8dB nominal level. Maximum level before clipping is +18dB.
Output level control may be used to compensate for extremes of
gain reduction.
600 ohm audio transformer.
+0, −½dB 20Hz–16kHz; +0, −1dB 15Hz–20kHz.
AGC disabled: Unity, −12dB to +12dB depending upon OUTPUT level.
Continuously variable from 1:1 through ∞ through −10:1.
Continuously variable from 1:1 through 10:1.
Infinite compression setting gives constant output level ±1dB
for 60dB change in input level.
Continuously variable function knob is used to set appropriate
compression/expansion ratio. Control operates parabolically to
give spread near center. Common settings are calibrated.
The ATTEN LIMIT and GAIN LIMIT controls serve to restrict the gain
control range to any value between 0 and 30dB in each direction.
AGC DISABLED: .05% between 20Hz and 20kHz. Typ. .02% at 1kHz. −20dB
AGC, +20dB output gain: Less than 1% above 100Hz, .5% at 1kHz.
At unity gain, output noise level is below −90dB.
Front panel meter provided which measures either absolute input
level, absolute output level, or gain on linear/log scale over 60dB.
DEFINITION: Numbers refer to the time required for the Omni-
pressor to change gain by 10dB in response to an input step
change of 10dB in infinite compression mode.
ATTACK TIME: Continuously variable from 100µs through 100ms.
RELEASE TIME: Continuously variable from 1ms through 1 second.
115V AC, 50–60 Hz ±12% or 230V AC, 50–60Hz ±12%; nominal 10 watts.
19in (48.26cm) wide; 3.5in (8.89cm) high; 9in (22.86cm) deep.
INPUT LEVEL
INPUT IMPEDANCE
OUTPUT LEVEL
OUTPUT IMPEDANCE
FREQUENCY RESPONSE
GAIN
COMPRESSION
EXPANSION
GAIN LINEARITY
FUNCTION CONTROL
LIMIT CONTROLS
DISTORTION
SIGNAL/NOISE
METERING
TIME CONSTANT
POWER REQUIRED
DIMENSIONS
SPECIFICATIONS
3
OMNIPRESSOR INTERFACE
The Omnipressor line inputs and outputs are transformer balanced, while the side
chain I/O is active balanced or unbalanced.
Transformer isolated, balanced or unbalanced +4dBu line input.
Accepts XLR or TRS connection (only one should be connected).
Transformer isolated, balanced or unbalanced +4dBu line output.
Accepts XLR or TRS connection (only one should be connected).
Active balanced/unbalanced +4dBu side chain input and output on
XLR or TRS connectors (only one should be connected).
Link multiple units in stereo or multi-mono setup using standard
TS or TRS patch cables. (See Linking section.)
LINE IN
LINE OUT
SIDE CHAIN IN/OUT
LINK IN/OUT
This control switches the Omnipressor in and out of an audio
circuit. When the switch is in the DOWN position (LED off) the unit
is completely relay-bypassed.
This control adjusts the input audio to both the gain control
circuit and the level detector (except when the side chain is used).
Note that this will have a direct effect on the threshold level.
This controls the mix of dry and processed signals for parallel
compression effects. Turn this control fully CCW for 100% dry signal
and fully CW for 100% wet signal.
This switch enables the external sidechain (if connected). When
the switch is in the DOWN position (LED off) the sidechain path is
disabled and the level detector recieves its signal from the input
signal. When the switch is in the UP position (LED on) the sidechain
path is enabled and the level detector gets its signal from the
external sidechain input.
This control determines the operating point of the Omnipressor. The
threshold set on this control is the “crossover” point for the gain
control voltage. For example, if the unit is set in a compression
mode, an input signal below the threshold will have its amplitude
increased, and an input signal above the threshold will have its
amplitude reduced.
This switch determines the frequency response of the level detector
circuit. In the DOWN position (LED off) the level detector has the same
frequency response as the gain control section. In the UP position (LED
on), bass signals are attenuated and have relatively less effect on the
overall compression/expansion operation of the Omnipressor.
This control varies the time the Omnipressor requires to respond to a
change in signal input level. Assuming a 10dB step increment in input
level, the attack time as set on the control is numerically equal to
the time required for the level detector to reach its final state with
respect to the new input level.
This control varies the time the Omnipressor requires to respond to
a decrease in signal input level. Assuming a 10dB step decrement,
the release time as set on the control is numerically equal to the
time required for the level detector to reach its final state with
respect to the new input level.
CONTROLS
LINE
INPUT LEVEL
MIX
SIDE CHAIN
INPUT THRESHOLD
BASS CUT
ATTACK TIME
RELEASE TIME
CONTROL AND INDICATOR DESCRIPTION
4
METER FUNCTION
FUNCTION
(Compress/Expand)
OUTPUT LEVEL
ATTEN LIMIT
GAIN LIMIT
LINK
POWER ON/OFF
This three-position switch controls the function of the meter. It
has no effect on the signal processing of the Omnipressor. In the
INPUT position, the meter reads the input signal level applied to
the unit. In the GAIN position, the meter reads the relative gain of
the Omnipressor and so gives an indication of the operation of the
gain control function. In the OUTPUT position, the meter reads the
output level of the Omnipressor. All level readings are in dBu.
This is the main control on the Omnipressor. It determines the
unit’s basic mode of operation. Fully counterclockwise, the Omni-
pressor gain varies sharply from full attenuation to maximum gain as
a threshold level is exceeded. As the control is rotated clockwise,
this action becomes less sharp until the gain varies only a few dB
from no input to full input. At the center divider, the Omnipressor
gain is constant regardless of input level. As the control is turned
clockwise from the center divider, the gain begins decreasing with
increasing input level. For small compression ratios, the gain will
vary only a few dB for large input changes. More rotation produces
substantial compression, until the point of infinite compression is
reached and the gain decreases 1dB for each dB of signal increase,
thus keeping the output level constant regardless of input. Rotation
past this point produces dynamic reversal, in which a high-level
input produces a lower-level output than does a low-level input.
Fully clockwise rotation results in full output attenuation above a
certain threshold Input.
This control increases or decreases the output level by ±12dB. This
can be used as a make-up gain control or simply to adjust overall
level. This control has no effect on compression ratio or other
operating parameters. It is equivalent to adding a simple amplifier
after the unit.
This control limits the maximum attenuation of the Omnipressor.
In its fully counterclockwise position, 30dB of gain reduction is
available. Fully clockwise, maximum attenuation will be about 1dB.
ATTEN LIMIT overrides the FUNCTION control.
This control limits the maximum gain of the Omnipressor. In its
fully counterclockwise position, 30dB of gain is available. Fully
clockwise, maximum gain will be about 1dB. This control overrides
the action of the FUNCTION control.
This switch enables unit-unit linking. In the DOWN position (LED
off) linking is disabled. In the UP position (LED on) linking is
enabled.(See Linking section.)
Applies power to the Omnipressor.
5
Becomes illuminated when the LINE switch is UP, indicating that the
Omnipressor is in-circuit.
Shows that the Omnipressor is operating in the gain-reduction mode.
Relative brightness indicates amount of gain reduction. Operation is
instantaneous, so that peak limiting is indicated even if the meter
has no time to respond.
Shows that the Omnipressor is operating in the gain-increase mode.
Relative brightness indicates the amount of gain increase. Operation
is instantaneous, so that short increases are indicated even if the
meter has no time to respond.
The METER is calibrated over a 60dB range in a linear/logarithmic
fashion, so that each 10dB takes up an identical space on the scale.
Center scale corresponds to an input level of 0dB, a gain of unity,
and an output level of 0dB, depending upon the setting of the METER
FUNCTION switch described earlier. The red arc occupying the upper
12dB of the scale applies in the output metering function, at which
time it serves to warn that the output amplifier is clipping.
INDICATORS
LINE
(red LED)
ATTEN
(green LED)
GAIN
(red LED)
METER
CONTROL AND INDICATOR DESCRIPTION (cont.)
6
LINKING
STEREO MODE
LINKING (default)
MASTER MODE
LINKING
VCA MODE
CONNECTIONS
In stereo mode all linked units follow the one with the most attenu-
ation. This is typically used in stereo, two-unit, configurations in
order to maintain a stereo image, but any number of units can be linked.
Only units that have their LINK switch enabled will participate.
To enable stereo mode linking, move the four internal link-mode
jumpers to the ST LINK position. These are found on the backside of
the front panel after removing the top cover. This is the default
mode as shipped from the factory.
In master mode all linked units follow the master unit’s gain. This
allows a single level detector (on the master unit) to control mul-
tiple channels of audio (on the slave units). In master mode, units
with their LINK switch enabled will act as slave units, while all
units with their LINK switch disabled will act as masters to all
down-stream slave units (until the next master unit).
To enable master mode linking, move the four internal link-mode
jumpers to the MTR LINK position. These are found on the backside of
the front panel after removing the top cover.
A single unit configured in master mode with its LINK switch
enabled, will function as a high-quality voltage controlled ampli-
fier (VCA). In this mode, a control signal is fed into the LINK
IN jack to control the VCA directly (See Application Note #3 for
details).
In stereo and master linking modes, units should be daisy-chained
in a loop, LINK-OUT to LINK-IN, as shown below. Standard TS or TRS
audio patch cables may be used.
7
MULTI-UNIT LINKING---BLOCK DIAGRAM
in in inout out out
OMNIPRESSOR 2 OMNIPRESSOR 3OMNIPRESSOR 1
LINK LINK LINK
YOUR OMNIPRESSOR LOVES YOU AND WANTS TO BE YOUR FRIEND!
If you don’t understand it, if you don’t fondle its controls properly, it will cause
you hours of confusion, and tempt you to dash it on the rocks or put it in a sack and
drown it. PLEASE READ this applications section before blaming your Omnipressor for
malfeasance or deviltry.
The Omnipressor, like most Eventide equipment, is a signal processor with wide-
ranging use. It is not the normal, tame limiter or compressor which only tries to
keep signals within a certain range. It is not a simple noise gate which is either
off, letting nothing through, or on, letting everything through at unity gain.
Rather, it is a special effects unit, which, in addition to the above, can generate
such effects as infinite compression, dynamic reversal, extreme expansion, etc. The
Omnipressor has a 60dB control range in addition to a wide dynamic range at constant
gain. Because of this wide range, it is possible to overload system components fol-
lowing the Omnipressor if it is used improperly. Note, for instance, that with the
output control wide open, and with the gain reading +30 on the meter, it is possible
to obtain up to 50dB gain from the unit. If you connected an amplifier with 50dB gain
between your console out and your tape recorder in, you might reasonably expect some
distortion, right? Right!
Before using the Omnipressor in a session or in a performance, familiarize yourself
with its operation. The ATTEN and GAIN LIMIT controls serve to prevent uncontrolled
operation by the novice user. Turn on the Omnipressor and turn the threshold control
to zero. With no input, the level detector stage is producing the maximum possible
control voltage. With no input, putting the FUNCTION knob in the expand section
causes a great reduction in gain. As the input increases, the control voltage gets
closer to 0, and the gain reduction decreases, until, at some point, set by the
threshold control, the gain starts increasing past unity (0dB). This is expansion
— increasing gain with increasing signal, thus increasing dynamic range. Note how
sharply the FUNCTION control varies the gain with no input signal. Also note that as
the signal level approaches the threshold, the function control has a less pronounced
effect, until, at the threshold, full rotation has almost no effect.
Experiment with the two LIMIT controls. Again remove the input signal. Turn the
two limit controls fully clockwise. Observe that the FUNCTION control can only vary
the meter by a few dB, despite the fact that with no input, maximum expansion or
compression should occur. Rotate the FUNCTION control to maximum expansion and vary
the ATTEN LIMIT control. Notice that the meter varies from negative full scale to
almost center scale. Now, rotate the GAIN LIMIT control. Note that this control has
no effect on the meter reading. Turn the FUNCTION control to maximum compression and
repeat the experiment with the LIMIT controls. Note that now the GAIN LIMIT varies
the meter reading from center to positive full scale, and the ATTEN LIMIT control has
no effect.
APPLICATIONS
8
The LIMIT controls are very important in setting up the unit. They can prevent
runaway gain, runaway attenuation, runaway engineer, and many other problems. For
instance, if you wish to increase average program level by 10dB, but limit compres-
sion to a maximum of 15dB, set the GAIN LIMIT control with no input and the FUNCTION
knob at full compress so that the meter reads +10 in the GAIN position. Now, turn the
FUNCTION knob to full expand and set the meter at −5 with the ATTEN LIMIT control.
You are now free to set the compression ratio, threshold, and time constant for the
most pleasing performance without worrying that you will get too much gain, too much
attenuation, or uncontrolled operation, regardless of signal levels or peaks. This
type of setability is perfect for sound reinforcement or broadcast use where unat-
tended operation is the rule and wild effects are not desired. Controllable com-
pression in sound reinforcement is particularly advantageous because feedback can be
prevented conclusively while still permitting maximum output.
Another control not customarily found on dynamic modifiers is the BASS CUT switch.
Unlike the LIMIT controls, it is not exceptionally useful. Its main application
is to prevent large gain variations from being initiated by low frequency signals.
A typical use would be in communications or advertising applications, where it is
frequently desirable to give a signal as much “punch” as possible. Information in
voice signals is generally carried in the range above 500Hz, although fundamentals
are present below this frequency. By using a short time constant and cutting bass
response, an improvement in intelligibility can be obtained in listening environ-
ments with less than optimum signal-to-noise ratios. Additional applications would
be in processing signal tracks with leakage present. If, for instance, the bass drum
leaked onto the voice track which you are limiting, the bass can be prevented from
affecting the gain control operation. (Note that this does not reduce the amplitude
of the leakage. Refer to the Noise Gate description for more information on reducing
leakage.)
The Model 2830*Au Omnipressor may be used as a fast peak limiter. By setting the
ATTACK TIME constant control to 100µs, the unit in effect no longer is an RMS
responding detector, but rather follows peaks in the input signal. At this rate a
single half cycle of 5kHz tone above the threshold is sufficient to reduce the Omni-
pressor gain by about 10dB. Smaller peaks at even higher frequencies can be limited
at this setting. Bear in mind that at very fast attack times, limiting is equivalent
to clipping, and if the signal level is frequently above the threshold, harmonic dis-
tortion will be increased.
The above material gives general considerations for the operation of the Omnipressor.
The remainder of this applications section is organized as a group of individual
“application notes.” If you have a specific application that you wish to make known,
please join our forum at eventideaudio.com.
9
As we state in our promotional literature, one of the novel features of the Omni-
pressor is its ability to make signals sound backward. This is a consequence of the
Dynamic Reversal feature, which enables loud sounds to come out more softly than
soft sounds. Speech waveforms, for instance, generally consist of loud peaks fol-
lowed by trailing-off envelopes. By making these envelopes louder than the peaks,
the illusion that the sound is coming out backward is generated. Likewise, drum
sounds consist of peaks roughly coincident with mechanical impact, followed by a
decay envelope. The Omnipressor amplifies this envelope and “swallows” the impact.
The reversal effect is not limited to voice and drums. In general. any material with
wide dynamic range can be “reversed.” Plucked string instruments, virtually all
percussion, and many natural sounds can be processed to good effect. Certain other
material does not sound good in the reversal mode. Specifically, program material
consisting of more than one type of sound will give inconsistent results at best.
Trying to process an entire program source rather than individual tracks will gener-
ally meet with ignominious failure, although solos can be picked out and reversed on
occasion.
CONTROL SETTINGS
LINE ON
FUNCTION −2 COMPRESS
ATTEN/GAIN LIMIT FULL CCW
TIME CONSTANT ATTACK 5ms, RELEASE 100ms
THRESHOLD 0
OUTPUT 0
METER GAIN
Experiment with the operational controls to obtain the most pleasing effect. It will
probably be desirable to limit the maximum gain somewhat with the GAIN LIMIT control
to prevent high noise levels with no signal. This applies particularly to taped
material in which noise reduction was not employed.
ADDITIONAL POSSIBILITIES
If you can make forward things sound backward, you should be able to make backward
things sound forward! Play a vocal tape backward and reverse the dynamics. The voice
should come out sounding almost normal, but the words will be pure gibberish. If you
want tremendous “punch” on recorded material, record it normally, and then play it
backward through the Omnipressor set barely into the reversal mode, and re-record
it. Playing the second tape backward (i.e. voice forward), should result in a signal
almost completely devoid of dynamic range. Also, you can use the second recording
as an opportunity to add some echo, which will then precede the signal in real time.
The reason backward compression is so effective is that the program material is
devoid of sharp attack transients which tend to bring down the succeeding program
material.
APPLICATION NOTE #1
“Your Backwards Omnipressor”
10
In a previous note, we discussed the possibility of compressing material in reverse
order to eliminate the compressor’s inherent problem with fast attack transients.
In a limiter, fast transients are in effect eliminated by signal clipping before
the system gain can adjust to the new level. In a normal compressor, short bursts
of high level material can get through before the gain can adjust. The first method
creates varying amounts of distortion. The second engenders such phenomena as
“p popping.” The unique ability of the Omnipressor to separate the gain control
from the level detector enables one to build what is most conveniently termed a
“predictive” compressor. Such a unit should go a long way towards eliminating the
unavoidable imperfections standard units have.
PREDICTIVE COMPRESSOR---BLOCK DIAGRAM
Connect an Omnipressor and an Eventide Digital Delay Line together as shown above.
Enable the sidechain input. What you have just fabricated is a compressor that can
read the future, or, in more common parlance, one which has a negative attack time.
It works as follows: A signal comes into the level detector via the sidechain, which
reacts to it depending upon the settings of the controls. Simultaneously, the signal
is fed into the delay line which delays it by one or more milliseconds. The signal
is then fed to the gain control section of the second Omnipressor. During this delay
interval, the level detector has reached the optimum output voltage for the input
signal, and before the time the signal reaches the gain control module, the gain has
adjusted to the level of the signal.
This predictive mode of operation requires some experimentation to match the
signal delay time to the Omnipressor time constant, but when the system is properly
adjusted, a very close approximation to the “ideal compressor” is realized.
LIMITATIONS
This type of operation is particularly effective in applications in which only one
signal must be processed. To maintain synchronism, a channel of delay is required for
each channel of audio, whether or not that channel is to be otherwise processed. This
would become cost prohibitive in any configuration exceeding stereo. There is much
room for experimentation. We would be pleased to know of your results and techniques.
APPLICATION NOTE #4
PREDICTIVE COMPRESSION
14
SC IN
audio
in inout out
OMNIPRESSORDELAY LINE
audio
Produkt Specifikationer
| Mærke: | Eventide |
| Kategori: | Kompressor |
| Model: | Omnipressor 2830Au |
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