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Eventide Omnipressor® Model 2830*Au
50-year-Anniversary Reissue of a Classic Dynamic Effects Processor
By Barry Rudolph
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| Eventide Omnipressor® Model 2830*Au (Front) |
The original Omnipressor Model 2826 was invented in 1972 by Eventide co-founder Richard Factor; his first prototype (with an edgewise meter) was shown in 1972 at Sound Exchange Studios in New York City.
While it may seem common-place today, one of the unit's major innovation back then was a "side-chain" control path connected to an early dbx VCA (voltage-controlled-amplifier) module provided by David Blackmer. This side-chain was driven by a specialized audio level detector circuit connected across the incoming audio signal.
Marketed as a strange and unconventional dynamics special effects unit, the original White Meter Omnipressor Model 2826 was a quirky, hard-to-use piece of gear that has puzzled everyone who tried it--even to this day. That same unit is now rare and very collectible that, if working, can sell for over $6,000.
Two years later with analog designer Jon D. Paul's 1974 redesign, the Model 2830 Black Meter Omnipressor debuted. It proved to be a more user-friendly and reliable version, and included calibrated controls for consistent operation.
The Model 2830*Au is Eventide's 50-year commemorative version that retains the overall front panel "look" of the 1974 model, with the exception that the white push-button switches are replaced with mini-toggle switches.
This new version adds a few front panel-controls and switches. There are switches to access to the rear panel side-chain balanced I/O and facilities to link any number of units to a single master unit (the Omnipressor is mono only), along with the addition of both Input and Output Level controls and a very useful Wet/Dry mixer.
What is it, How Does it Work?
The Omnipressor is a professional-quality, all-analog dynamic range modifier, capable of dramatic real-time effects. To help you achieve the desired results, there are specialized controls, LED indicators, and a meter that uses a logarithmic amplifier to show the Input and Output signal levels, plus any additional Gain reduction or attenuation.
There are many possible uses for adjustable, high fidelity dynamic modification. You can fix noise problems, un-compress over-compressed audio or realize exotic sound-designs.
I used it all the time as an everyday, very clean-sounding and limiter/compressor/gate. But, to take full advantage of this unit's capabilities, a solid-understanding of the way compressors, expanders, limiters, noise gates i.e., all dynamic processors--operate is very helpful.
The manual's first page shows designer Richard Factor's original transfer function graph indicating the relationship between the Output signal, indicated on the (Y) vertical axis going from -30dB to O dB to +30dB, and the Input signal on the (X) horizontal axis, also from -30dB to 0dB and up to +30dB.
There is a horizontal, flat "center-line," with a pivot point in the precise center of the graph, indicates 0dB, or unity gain, and shows where both the Input and Output levels are equal with no change.
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| Eventide Omnipressor® Model 2830*A (Rear Panel) |
All transfer function lines are shown without the influence of attack and release time settings. To help understand the abilities of the Omnipressor, there are five more lines overlaid on the same graph that depict the unique transfer functions possible above and below a set Threshold level. These lines pivot at the same point on the horizontal center-line.
The center-line and pivot point concept is carried over to the Omnipressor's front panel controls and the meter's operation. When starting a new setup during a session, a good starting position for all control knobs is straight up at 12 o'clock.
The manual's Application Notes has the starting positions for all the controls for the many uses of the Omnipressor and what to expect to hear and experience when used on a particular source audio. These notes are a great way to learn the controls and what they do.
Controls and Metering
Starting at the left side of the front panel are Threshold with a -25db to +15dB range, Attack Times range from a super-fast 100-microsecond to 100-millsecond. Release Times range from 1-millisecond to a full second. I used the straight-up starting positions of these controls when first developing a sound.
Below these three controls are switches and controls starting with: Bypass In/Out (called Line), and Input Gain (trim) from -60dB to +12dB. The Omnipressor Model 2830*Au has both input and output transformers that were an option on the previous model. There is an in/out switch for Bass Cut, a steep, 200-Hz high-pass-filter working only on the side-chain signal.
Next is a Wet/Dry Mix control followed by a switch for using an external side-chain for control if connected. The last switch is a three-way toggle for the unit's backlit, black meter.
The center of the Omnipressor is dominated by a large meter that indicates either the Input or Output level or Gain. Gain is added to the output signal in the case of expansion, or subtracted in the case compression or limiting. With no input audio, the meter, when switched to read Gain, should be straight up at 0dB.
There are also peak indicating LEDs that read moments much too fast for any mechanical meter to display. The green Atten LED shows instantaneous attenuation or gain reduction. On the right side is a red Gain LED showing added gain.
With the Meter switch in the middle Gain position, and all other switches, controls and the Function knob straight up in their center positions, the meter's needle should be in the center position and read 0dB when no audio is passing through the unit.
Function Control
The Function knob's operation has always been the source frustration and confusion for many engineers ever since I first used the white-meter unit in 1974. Mainly because all the possible dynamic functionality of the Omnipressor is available using a single large, smooth-working Function knob.
Using a single knob, you can continuously go from expansion ratios at full counter-clockwise through compression ratios starting at 1:1 and ending with infinity : 1, then onto negative compression ratios at -0.1: 1 at fully clockwise.
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Atten Limit and Gain Limit Controls And More
There are two controls, called Atten Limit or the range of gain reduction from -30db to 0dB and Gain Limit or the range of added gain from 0dB (or no additional gain) to +30dB of added level.
Understanding these two controls' operation is key to using the Omnipressor effectively.
One note: when the Gain Limit control is above the straight up position up to +30dB, the system noise floor will be heard! Check that the audio coming in to the Omnipressor is as clean and noise-free as possible.
Finally, continuing on the right side of the front panel, the unit includes is an external link switch for connecting another Omnipressor designated as master. The last control is an Output level Trim control that varies the output from -12dB to +12dB. Turning this control fully counter-clockwise does not shut the output off. Again, I leave this control in the straight up position so I can fine tune the final output level when needed.
In The Studio--Then and Now
My very first experience was back in 1973 was memorable and love at first sight since I barely knew what I was doing trying out a very "wobbly" White Meter Omnipressor Model 2826. I was recording a rock band at Larrabee Sound in West Hollywood.
The band's father/manager hired veteran session drummer Hal Blaine to play on the record instead of their own drummer. Guitarist Brian Ray--who later became Etta James' musical director, now plays guitar and/or bass in Paul McCartney's band. Brian told me this was his first session in a proper recording studio with a studio musician and a professional recording engineer (me!).
I used the dynamic reverse mode on Blaine's snare drum mic and I distinctly remember the "look" on Hal's face when he heard the first playback in the control room. The attack of the snare drum was greatly reduced (super-fast attack time) with the sustain and after-portion of the sound drastically increased in level.
Hal's steady time keeping and consistent recording level allowed this effect to be almost machine-like. I would add that using the Omnipressor on live microphones (vs already recorded tracks) is the most effective way to achieve dynamic reversal effects.
I found this updated model much quieter and more precise and adjustable compared to original. Back in 1973, I was careful not to tweak parameters while recording musicians as I would with other processors. The Function knob was very sensitive before Jon D. Paul's re-design.
Tracking The Band
I first tried it on a recorded bass guitar like a regular compressor set to 2:1 ratio. But I was then able to (among other lucky accidents) overload the input section by cranking the Input level trim and using extremely very fast and release times and arrive at a bass guitar sound rich with harmonics and loud attacks. I could precisely dial it in using the Attack time and the Wet/Dry control.
In general, for regular compression chores, I found lower ratios such as 1.2 :1, 1.5 up to 8:1, fine for the most transparent sound with up to 10db of gain reduction as long as the Attack and Release times are not too fast and the Atten Limit is not more than about -10dB. If you require some of the source's transients intact, just blend them back in with the Wet/Dry mix control.
I experimented with negative compression ratios such as -2:1 to -0.1:1 continuously adjustable on the Function knob starting just after the infinity : 1 position. Negative ratios give the "backwards" affect because the output level increases during the release time.
A picked acoustic guitar sounded decidedly Rock N' Roll using a negative ratio of -0.2:1 to -0.1:1 with fast attack and release times. Atten Limit was at 12 noon and Gain Limit was at +10. Threshold was +5, and Input trim was straight up pushing in more input level into the unit. I use Wet/Dry Mix straight-up as well.
Expansion mode worked to recover an overly compressed (low level) brass track. I tried to reverse the 2:1 compression ratio. The Function knob was somewhere between 1 and 2 on the expansion side and the Atten and Gain Limit controls were fully counter-clockwise. Threshold was straight up at -5dB.
With no input signal, the meter read -20--exactly the Atten Limit setting and at a 1:3 expansion ratio, the guitar started to sound bad, especially on sustained notes. The 1:2 expansion ratio sounded better and adding a little of the Wet/Dry smoothed things out. When this is working correctly, you'll see the green and red LEDs alternately blinking to indicate gain reduction and boosting as required for reconstructing the dynamic range.
I wanted to try expanding a mono room track to see if I could get something special. It brought up the tone of the room and especially the low-level subtle things--sticks on the ride cymbal and even a squeaky bass drum pedal!
A Great Processor!
The reissue of the Omnipressor Model 2830*Au lives up to the 50-year legend started in the early '70s. Now that I have used both the early White Meter version and this new and updated one, I can verify that this is the ultimate fulfillment of Richard Factor's truly original idea.
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