Eventide Omnipressor

Eventide’s unique, and uniquely versatile, hardware compressor has had a well‑deserved reissue, with sympathetic improvements to update it for the modern studio.

From the groundbreaking H910 Harmonizer to their current H90 stompbox, Eventide are best known for their digital gear. But back in the ’70s their catalogue included a number of analogue processors. Perhaps the most interesting of them was the Omnipressor, now reissued to celebrate its 50th anniversary.

Like the original, the reissue Omnipressor is a smart black 2U rack unit. Unlike the original, thankfully, its audio I/O is on conventional connectors rather than screw terminals: line in, line out, side‑chain in and side‑chain out are on both XLRs and quarter‑inch jacks, while stereo link in and out are on jacks only. On the front panel, the chunky white plastic buttons of the ’70s incarnation have been replaced by switches. This has freed up space for Eventide to add quite a few useful new features.

There’s now an input gain control in addition to the threshold dial, plus a wet/dry mix control, while today’s Omnipressor can independently be stereo linked and externally side‑chained, with convenient switching from the front panel. Finally, the output gain control is now continuously variable over a ±12dB range, in place of the switched 0, +10 and +20 dB choices on the older version. Happily, the all‑important meter looks very similar, and build quality on the reissue seems excellent — quite possibly better than on the originals.

Threshold Of Pain

Calling the Omnipressor a compressor is like describing a Swiss Army knife as a knife. It’s much, much more than that, but its operation is also fundamentally different from that of conventional dynamics processors, and can be confusing at first. Perhaps the best way to explain this is as follows. Most compressors start to apply gain reduction only once the signal level exceeds the threshold value. Likewise, expanders apply attenuation only to sounds below the threshold. In the Omnipressor, by contrast, dynamic changes are by default symmetrical either side of the threshold.

Consider a typical application for compression on a vocal track. On a standard compressor, we’d set the threshold level such that loud peaks exceed it and trigger gain reduction, thus reducing the average level of the vocal and its dynamic range. On the Omnipressor, though, the signal level doesn’t just get pulled down towards the threshold when it’s loud; it also gets pushed up towards the threshold when it’s quiet. The Omnipressor can act as an expander, too, in which case this equation is reversed. Signals below the threshold are made quieter, as on a standard expander, but signals above the threshold are also made louder.

In other words, the Omnipressor’s...