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Eventide Omnipressor Model 2830*Au—A Mix Real-World Review

The Mix review team takes on the 50-year-anniversary reissue of a classic dynamic effects processor: The Eventide Omnipressor!

Eventide Omnipressor Model 2830*Au—A Real-World Review

The original Omnipressor Model 2826 was invented in 1972 by Eventide co-founder Richard Factor; his first prototype (with an edgewise meter) was shown the same year at Sound Exchange Studios in New York City.

While it may seem commonplace today, one of the unit’s major innovations back then was a “sidechain” control path connected to an early dbx VCA (voltage-controlled amplifier) module provided by David Blackmer. This sidechain was driven by a specialized audio level detector circuit 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; if working, one can sell for more than $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 of the white push-buttons being replaced by mini-toggle switches.

This new version also adds a few front-panel controls and switches. There are switches for accessing the rear-panel, sidechain 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.

Eventide Omnipressor Model 2830*Au Eventide Omnipressor Model 2830*Au


The Omnipressor is a professional-quality, all-analog, dynamic-range modifier capable of dramatic real-time effects. 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 a multitude of uses for adjustable, high-fidelity, dynamic modification. You can fix noise problems, un-compress over-compressed audio, or realize exotic sound-design elements.

I used the Model 2830*Au all the time as an everyday, clean-sounding limiter/compressor/gate.

To take full advantage of this unit’s capabilities, a solid understanding of how compressors, expanders, limiters and noise gates—i.e., all dynamic processors—operate is helpful.

The manual’s first page shows product designer Factor’s original transfer function graph, indicating the relationship between the Output signal, indicated on the (y) vertical axis ranging from -30 to O to +30 dB, and the Input signal on the (x) horizontal axis, also from -30 to 0 to +30.

A horizontal, flat “center-line,” with a pivot point in the precise center of the graph, indicates 0 dB, or unity gain, and shows where both the Input and Output levels are equal with no change.

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.

This center-line and pivot-point concept is carried over to the Omnipressor’s front-panel controls and the meter’s operation.

When creating a new setup during a session, a good starting position for all control knobs is straight up at 12 o’clock.


Starting at the left side of the front panel are Threshold with a -25 to +15 dB range, Attack times range from a super-fast 100-microsecond to 100-millisecond. Release times range from 1 millisecond to 1 second. I used the straight-up starting positions 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 -60 to +12 dB. The Model 2830*Au has both input and output transformers, which was 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 unit 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 case of compression or limiting. With no input audio, the meter, when switched to read Gain, should be straight up at 0 dB.

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 0 dB when no audio is passing through the unit.

The Function knob’s operation has been a source of frustration and confusion for me since I first started using the original, white-meter unit in 1973. Why? All of the Omnipressor’s dynamic functionality is available using this single large, smooth-working Function knob.

From a single knob, you can continuously go from expansion ratios at full counterclockwise through compression ratios starting at 1:1 and ending with infinity:1, then onto negative compression ratios ending at -0.1:1, fully clockwise.

The next two controls—Atten Limit, or the range of gain reduction from -30 to 0 dB, and Gain Limit, the range of added gain from 0 dB to +30 dB of added level—are key to using the Omnipressor effectively. One note: When the Gain Limit control is above the straight-up position, up to +30 dB, the system noise floor will be heard! Check that the audio coming into the Omnipressor is as clean and noise-free as possible.

Finally, continuing on the right side of the front panel, the unit includes an external link switch for connecting another Omnipressor, as well as an Output level Trim control that varies the output from -12 to +12 dB. Turning this control fully CCW 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


My first experience with an Omnipressor was back in 1973 and it was memorable, even love at first sight. I was recording a rock band at Larrabee Sound in West Hollywood, and I barely knew what I was doing when I tried out a very “wobbly” White Meter Omnipressor Model 2826.

The band’s father/manager had hired legendary session drummer Hal Blaine to play on the record instead of their own drummer.

Guitarist Brian Ray—who later became Etta James’ musical director and now plays guitar and/ or bass in Paul McCartney’s band—was playing on his first session in a proper recording studio with a professional recording engineer (me!).

I used the dynamic reverse mode on Blaine’s snare drum mic, and I distinctly remember the “look” on his face when he heard the playback in the control room. The attack of the snare was greatly reduced (super-fast attack time), with the sustain and after portion of the sound drastically increased in level. The drummer’s steady time-keeping and consistent recording level made this effect almost machine-like.

I found this updated model much quieter, and more precise and adjustable, compared to the original. Back in 1974, I was careful not to tweak parameters while recording musicians, at least not as I would with other processors.

The Function knob was very sensitive before Jon D. Paul’s redesign.


I first tried it on a recorded bass guitar just like a regular compressor set to 2:1 ratio. I was then able to (among other lucky accidents) overload the input section by cranking the Input level trim and using extremely fast attack and release times, arriving at a bass guitar sound rich with harmonics and loud attacks. I could precisely dial it in using the Attack time and Wet/Dry controls.

For general, regular compression chores, I found lower ratios, such as 1.2 :1, 1.5 on up to 8:1, fine for the most transparent sound, with up to 10 dB of gain reduction as long as the attack and release times are not too fast and the Atten Limit is not more than about -10 dB.

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 “backward” effect 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 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 more input level into the unit. I used 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 CCW. Threshold was straight up at -5 dB.

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.


This reissue of the Omnipressor Model 2830, lives up to the 50-year legend. 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.