The Mozztronics CO-2 Opto-Comp Optical Compressor is an optical compressor pedal made by Mozztronics in Australia. It uses an optical element for the compression, and Pedal of the Day describes the circuit as solid state, built to capture how old vacuum tube compressors sounded1. It sits in the wider family of compressor pedals, and it was designed from the start to work on both instruments: the review states the design goal "had to be useful for both guitar and bass, and had to be different from what is already on the market"1.
The controls: Gain, Ratio, Threshold, Range and Dynamics
The CO-2 carries five main controls, each with a distinct job:
| Control | What it does |
|---|---|
| Gain | Make up gain, so you can adjust for the same volume from bypass to effect active1 |
| Ratio | Controls the amount of compression, from barely on to super squishy1 |
| THReshold | Adjusts the point at which the compressor starts to operate1 |
| Range switch | Selects the frequency range the compressor sensing uses for its operation; up is full range1 |
| DYNamics | Mixes in a little of the raw uncompressed signal to add back some dynamics1 |
The DYNamics control is the pedal's take on parallel compression. As Pedal of the Day puts it, "DYNamics uses an old studio trick of 'parallel compression', by mixing in a little of the raw uncompressed signal to add" back dynamics1. In practice, that means you can set a heavy Ratio and still keep the natural rise and fall of your playing, because the uncompressed signal sits underneath the squashed one.
The Range switch is the other shaping tool worth understanding. It selects the frequency range the compressor sensing uses for its operation, with up being full range1. On bass, that kind of detector shaping is a common way to steer how the compression responds to low notes versus attack, and the CO-2 makes it a front-panel choice.
The release behavior is also more involved than a single knob suggests. While you can set the release with the potentiometer, an internal added release works in parallel and varies depending on the input signal1. That interactive release is what lets the pedal tighten up on fast passages and breathe on slower ones without you touching anything mid-song.
What reviewers said
Pedal of the Day reviewed the CO-2 on 28 April 2021 and was direct in its verdict1:
"What an excellent-sounding compressor"
The same review credits Mozztronics with "coming up with a solid state circuit that captured how these old compressors sounded"1, framing the CO-2 as a modern solid state answer to vintage tube compressor designs rather than a copy of any one of them.
Videos
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Questions
What does the Dynamics knob do on the Mozztronics CO-2?
The Dynamics control uses what Pedal of the Day calls an old studio trick, parallel compression, by mixing a little of the raw uncompressed signal back in with the compressed signal. That adds back some of the natural dynamics that heavy compression can flatten out, so you can squash the signal and still keep it breathing.
Does the Mozztronics CO-2 use parallel compression?
Yes. The Dynamics control brings in parallel compression, mixing a little of the raw uncompressed signal with the compressed signal to add back some dynamics. Alongside that, the CO-2 has an interactive release: while you set the release with a potentiometer, an internal added release works in parallel and varies depending on the input signal.
What does the Range switch do on the CO-2 Opto-Comp?
The Range switch selects the frequency range the compressor sensing uses for its operation. Up is full range, meaning the detector listens across the whole signal. Setting it differently changes which part of your playing drives the compression, which is a useful shaping tool for both guitar and bass.
Is the Mozztronics CO-2 analog?
The CO-2 is a solid state circuit that uses an optical element for the compression. Pedal of the Day describes Mozztronics as coming up with a solid state circuit that captured how old vacuum tube compressors sounded, so it is an analog-style optical design rather than a digital modeling pedal.
Can the Mozztronics CO-2 be used on bass?
Yes. Pedal of the Day reports that the design goal for the CO-2 was that it had to be useful for both guitar and bass, and had to be different from what was already on the market. The Range switch and the parallel compression blend are the kinds of controls that make that dual use practical.
Sources (1)
- Mozztronics CO-2 Opto-Comp Optical Compressor, Pedal of the Day, 2021-04-28
