Ashly Audio have been building high‑quality outboard processing equipment for as long as I can remember, but they've recently redesigned their parametric equaliser, and it's now available in two formats: the single‑channel PQX 571 and the dual‑channel PQX 572. Both units are identical, apart from the number of channels, and feature electronically‑balanced inputs and ground‑lifted, unbalanced outputs on both XLR and stereo jacks, as well as on a terminal strip. The mains cable is fixed rather than in the form of a detachable lead.
The PQX 572 is rather generous in the amount of EQ control provided; each channel has five independent parametric filters, plus two variable‑frequency shelving filters (one high‑pass and one low‑pass). Each filter section has its own bypass button with status LED, and there's also a master level control and master EQ In/Out button at the right of the front panel. A practical touch is the inclusion of a clip LED next to the master Level control, which comes on if any of the filter sections are being driven close to the point of clipping.
The high‑ and low‑pass sections appear to be 6dB/octave filters, and operate over the ranges 40Hz to 400Hz and 1.6kHz to 16kHz respectively. A dual concentric knob system is used where the inner knob alters the cut or boost (+/‑15dB) and the outer knob adjusts the shelving frequency. I'm actually a great fan of variable‑frequency shelving filters, and find them useful in lots of situations where conventional EQ fails to hit the spot, although in this case, I feel 12dB/octave slopes would have been more useful.
All five parametric sections are identical, and all cover the frequency range 20Hz to 20kHz, though there is a x10 Range button which effectively provides two ranges: 20Hz to 2kHz and 200Hz to 20kHz. As with the shelving filters, a dual‑concentric knob system is used, this time to control the frequency and the bandwidth. The Bandwidth control covers the range 0.05 octaves to 3.3 octaves, and is calibrated in octaves rather than Q values, which makes it more intuitive to use. A separate Level control is used to set the degree of cut or boost within a +/‑15dB range. When an EQ section is switched in, a green LED comes on to provide visual confirmation.
Technically, the PQX 572 is pretty conventional, using state‑variable filters based around the 4558 op‑amp chip for each of the parametric sections. The same op‑amp is used for the shelving filters and for the electronic input balancing. All the circuitry is run from 18V rather than the more usual 15V, presumably to make the best use of the available headroom, and the general standard of design is up to the quality you'd expect from Ashly.
In practice, I found that I rarely needed to use all five parametric bands, especially with those very useful shelving controls to help me along, but it's always better to have power in hand than to run out halfway through a job. As a basic parametric EQ, the PQX 572 is pretty straightforward to use, and the circuitry has plenty of dynamic range, so you aren't likely to get the thing clipping unless you start to use improbable amounts of boost in a section of the audio band that's already pretty hot.
Tonally, the equaliser is clean, precise and very quiet, and used with care, it can save the day in a number of situations ranging from mix sweetening to customising the sounds of individual instruments. However, Ashly don't claim that their EQ adds any mysterious psychoacoustic benefits, as is the case with certain tube EQs! A good description would be workmanlike — the PQX 572 just gets on with the job without fuss, and has sufficient range for notching out spot frequencies (such as hum), or for general tonal control using wider bandwidth settings.
Given the very realistic price of the PQX 572, and the fact that it has five bands of fully parametric EQ plus two bands of shelving EQ per channel, I have to give this equaliser an unqualified thumbs up. It's by no means the only good parametric around, but considering the facilities it offers and the pedigree of the Ashly brand name, it has to be considered good value.