The advantages of using an audio compressor in live or studio applications are enormous. Compressors give us better control over a signal's dynamics, and they can also produce interesting and desirable "effects" on certain sources. Many of us compress kicks, snares, electric basses, horns and vocals almost automatically, looking for that ideal sound within the vast mix of sources arriving at a console.
For the author of these lines, the compressor is undoubtedly an attractive tool, and an almost indispensable one at many concerts.
Basic
For this task ARX offers us the DDP 1 (976 euros + VAT), a dual dynamics processor. "Dual" because it actually consists of two compressor/gate/limiter units, something common in other designs, even from different manufacturers. In fact, it is two identical compressors in a single rack unit, with the advantage that the settings of one channel can be linked identically to the second, which is useful, for example, in stereo applications (such as compressing a subgroup carrying an entire horn section evenly).
On the rear panel we find the full set of connections, including an IEC power inlet. Each channel has balanced jack and XLR inputs and outputs, plus a Sidechain input in insert mode (which lets us control the compression according to the signal level we apply to this input). A sound panel, similar to the standard layout.
The front panel has all the basic controls needed for setup, identical for each channel. From left to right we find a knob for the gate threshold level (from -60 to +6 dB) and a switch that turns it on or off at will. Perhaps because of its "basic" orientation, it lacks other controls that many of us professionals use to shape a signal's dynamics further; for example, I missed a control that would let me adjust the gate's response time. It would be the icing on the cake if it also had a knob for the amount of attenuation applied, but that's another story.
The next section is the one dedicated specifically to the compressor. It has the most common controls: threshold level (from -40 to +20 dB), compression ratio, output gain level (+/- 20 dB) and limiter (from -3 to +18 dB). In the center, two rows of LEDs show us the input and output level (depending on the position of a switch) and the amount of compression applied. The second channel offers identical features. The only addition is the switch that enables the stereo link (Stereo Link).
Put to the test
I used the ARX DDP 1 in several sessions, all of them live sound applications. The compressor had to tame the strong dynamics of a kick drum and a bass, or, in another situation, control the levels of a delicate youth choir made up of about 20 young singers.
Probably because I'm used to working with a specific compressor, I'll say again that I missed some controls. Perhaps for that reason, I found the DDP 1's noise gate very abrupt, which was obvious with the choir and forced me to turn that function off (the gate closing was obvious, since the ambient noise was noticeable). Nor did I manage to get a punchy, precise kick drum sound, since I couldn't precisely control the compressor's attack times, although it was very easy to find the perfect combination for an impressive, if less precise, sound (which leads me to think that the DDP 1 is ideal for those who want to start using a compressor for the first time, since this is one of its strong points: it is quick and easy to operate). One thing that surprised me was the use of the green LED in the In/Out (switch) section. The LED lights up green when the compressor is not working and goes off when we activate it. A bit odd.
Even so, the DDP 1 has more advantages. First, inside it there is a passive RFI filter that, before any processing takes place, rejects much of the radio-frequency interference that may appear. This way we can easily get rid of the occasional stray noise. Also useful is its "sliding bias" mode, which switches to AB mode when signal levels are below 4 dB and to A mode when they exceed that figure. This ensures minimal added noise and the lowest possible introduction of new distortion at any signal level (especially at low levels).
In fact, these advantages lead me to suggest using it in the final stages of the mix, whether in live applications just before feeding a power amp or crossover, or in the studio as a step before the final recording (for example, at the input of a tape recorder).
Conclusion
Dynamics processors like the one reviewed here (which includes a gate, compressor and limiter) are necessary tools in many audio applications, both live and in the studio. The ARX DDP 1 will be useful in the final stages of the mix, regardless of the setting, although it falls short when you want to be precise and surgical on certain channels. Bearing in mind how easy it is to use, it is sure to satisfy its owner.
