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Omnipressor: Anatomy of a Preset

The original effects processors of the ‘70s and early ‘80s didn’t have "presets." They had knobs, buttons, switches, and blinking lights just as the gods of rack-mount equipment intended them to have. A delay line had a knob for adjusting the delay. An equalizer had a few knobs or maybe a group of slide faders for adjusting the level at various frequencies. Then things got complicated. Unlike the original processors that used shift registers for delay or even circuitry for frequency adjustment, they now all have DSP chips and microprocessors that do everything. You can’t connect a knob to an address line or a delay-tap switch to a data bus, so you rely on software that talks to you and to the DSP. This software tells the chip how to create the effect you want, and allows you to "tweak" the effect by the adjustment of parameters.

The utility of an effects processor is, in large part, determined by this software and by the creativity and initiative of the people who tell it how to create the effect. Simple effects still have their uses, of course, but things start getting interesting when you combine, for example, a number of delays with gain and frequency-dependent processes, and then automatically pan them among outputs. The person who purchases a processor for use in his studio is rarely an expert in DSP programming and/or effect design- he is interested in getting the right sound for his mix. Because this is true in most cases, manufacturers of effects equipment concentrate on creating “presets,” combinations of DSP processing program fragments that combine to create something musically (or eccentrically) useful. Because these presets are composed of several elements, each of which may be adjustable over a musically useful range, the “controls” of these elements, such as amount of delay, feedback gain, or whatever, are attached by the software program to user adjustments-knobs, faders, buttons, etc. These are the adjustments referred to as “parameters.” Most commercial effects processors use this strategy. Folks at the factory put together presets, give them whimsical names, screen them on the panel or put them in software menus, and then flog the product citing the number of presets. For the majority of customers, this is fine. But what if they want more?

Beyond Presets

By "more" I mean the ability to create sounds "limited only by their imagination?" Back in the days of modular synthesizers it was possible to do this. You bought a number of VCAs, VCOs, mixing modules, ring modulators, etc., and then “patched” them together with pieces of wire. There were limitations: Modules were expensive. Modules came in a limited variety. The modules were analog and so were a bit unstable and somewhat noisy. And, they worked largely with their own signals and couldn’t process external inputs in a very useful way.

Even so, some very creative and very interesting material came from the old Moog, Arp, and Buchla hardware. So what if it filled the room and required enough patch cords to circle the Vampire Stoat building? Now that it is possible to create these (and many, many more!) modules digitally, anyone can have “more.”

This article is being written with three purposes in mind:

  1. To show how a current generation signal processor (The Eventide Orville and the earlier DSP4000 series) can be used to create sounds “limited only by ones imagination.”
  1. As a practical example of this, to provide a mini-tutorial on how at least one vintage product-the Eventide Omnipressor-has been re-created.
  2. To justify the time that I spent recreating the Omnipressor, a really neat box which otherwise would remain a footnote in audio history and unavailable for experimentation.

Hopefully others will be encouraged by this example to experiment with their Eventide DSP units to create their own “signature” effects and perhaps even other product recreations. 

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