In 2014, SonicScoop ran a good article detailing a few engineers' go-to mix-bus chains. I was surprised to see the substantial pile of plug-ins and outboard units (though nearly all plug-ins) that everyone strapped across their 2-bus. I expected more "I leave that for the mastering engineer" puritanism, but maybe those days are over. Personally, I've tried all kinds of things on my mix bus, but lately I've been keeping it simple — a gentle EQ for brightness and air, and a single compressor for grit and cohesiveness. I feel like this keeps me on my toes and forces me to get my mixes there rather than counting on magic. Usually. Ahem. 

For EQ, I've tried a few things, but I've mostly settled on the UAD Precision EQ, with 1-2 dB shelving boosts around 22 kHz and (sometimes) 55 Hz. That works pretty well, but the quest for tone never dies, so thanks to a few friends, I started eyeing analog Baxandall-inspired program EQs, like the Dangerous BAX [#79]. Baxandall EQs act sort of like gently-sweeping, infinite shelves; and they are generally considered very smooth, with minimum phase delay and without audible resonances. The XQP 535 Program EQ is one candidate that caught my eye. 

Based in Oklahoma, XQP is a funky, two-person operation specializing in 500-series modules and guitar pedals. They answer emails quickly. Their manuals are short, funny, and well-written. Every product page on their website includes a schematic. They build their products in the USA. They offer a 10-year warranty. And god bless them, they put a grab handle at the bottom of their modules, so it's much easier to get them in and out of a 500-series frame. 

The XQP 535 is a two-band EQ, with two frequency ranges for each band. It's easy to use; the faceplate simply has two buttons to select each band's frequency, and two cut/boost knobs. Since I figured most 535 applications would be stereo, I asked for a pair to review. After installing them, I immediately tried applying them to a number of my completed, unmastered mixes. My first impression was, "Whoa! Everything sounds bigger." Of course, that's to be expected from the smiley-face "turn up the bass and treble on the hi-fi" effect, but with careful listening, I decided this wasn't just a cheap thrill. The high band provided air and brightness without making cymbals and vocals trashy or harsh, and the low band let me dial in energy that I didn't know I was missing, without adding mud. On some sources, the two high-frequency range selections — 10 kHz and 15 kHz — don't differ as much as you might expect, but overall, I found that I generally preferred the 15 kHz setting. The low frequency settings — 50 Hz and 100 Hz — are more obviously different; in my mixes, they equated to "kick drum" versus "bass guitar" emphasis. The manual explains that these frequency markings are fairly arbitrary. Actually, the slope of the classic Baxandall treble curve starts at 1 kHz, and it gradually rises to about 35 kHz or 45 kHz on the 535, depending on the selected frequency range. XQP chose to label the ranges with frequencies they considered representative of what you're hearing. Personally I'd be happy with 35/45 kHz labels, but with only two choices, it barely matters. Just use your ears. 

Next, I tried the 535 on a few individual sources. The high band provided pleasant top end on vocals that were tracked through a vintage AKG C 414 EB. The vocal sounded "airier" but wasn't nasty or sibilant. On drum subgroups, the 535 does what you would expect — more openness and clarity on the cymbals and crack of the snare, without harshness, and nice, usable low end. (The circuit also includes a fixed 20 Hz high-pass filter to reduce inaudible infrasonics.) The 535 imparts no discernible distortion, and it feels "smoother" than traditional shelving EQs. It just magically does its thing. 

I ended up leaving the 535 on my mix bus for the next couple of months. It's on at least a half-dozen records that I mixed. I liked it a lot; it really seems to add "more" without nasty side-effects. But that smiley-face effect is real; on an entire program these EQ curves are like candy, especially when they're so oddly smooth. So it's important to monitor at different volumes with the EQ in and out, and be sure that you haven't gone too far — and that the EQ is really improving things. Sometimes, similar to that "forcing myself to get there" thing, I used the 535 as a reminder of details I needed to chase down in my mix; listen with the EQ engaged, then disengage and work on individual sources to bring out more high-frequency detail — in effect, "competing" with the 535 version. 

My friend Brad Boatright runs Audiosiege in Portland. He's a great mastering engineer, and he's had a Dangerous BAX in his rack for years. Brad was interested in trying the XQP 535, so I shipped my pair his way. He spent some time with the 535s and lent them to a few engineers in his building. Here's what Brad wrote back: "Overall, I really dig these EQs. They do what they are designed to do, and my complaints are selfish, 'if I were to design this for myself' criticisms. Sonically, they give the signal a lift on both ends of the frequency spectrum that you notice slightly when engaged, but really miss when disengaged. We first tried them on a stereo mix. It was easy to dial in and settle on a sound, thanks to the minimal options of only two frequency choices per band. On a set of Royer overheads, they worked great for tracking, since the Royer ribbons tend to be a little dark. It seems like tracking might be the strong suit for these — though in that application, they could also benefit from a set of filters. For example, a low-pass filter could help control low-end resonance in guitars. 

"I'd like to see a larger gap between the two provided frequency choices, since I sometimes use a high-shelf set lower in the spectrum to help snare drums pop more. The lack of linked controls makes using a pair a bit more difficult for stereo work. The lack of stepped controls or fine lines of measurement makes it difficult to recall settings. The pots are very light and smooth. It doesn't feel like they would resist a bump from a cable or even a vibration over the course of a session. But these physical limitations are really not indicative of a cheap sound, and it's obvious that the EQs are intended to be a simple and affordable way to give a signal a natural, gentle boost, or tilt the frequency spectrum. 

"I feel like my Dangerous BAX smokes the 535, but that's a bit unfair, because the BAX has a lot more features and frequency choices. [And costs 3.5× as much! -Scott] Sonically it's close, but the BAX has something that works on the entire program rather than just the extreme ends, if that makes any sense." 

I agree with Brad about the pots; they move too easily, and recalls can be tricky with only a few dots to go by. But with analog recalls, I try to embrace "close enough is close enough." (I am not a mastering engineer.) I also agree that the 535 doesn't sound cheap. These are really nice EQs, and at $700 a pair, they are well worth your consideration. 

While I was asking XQP for demo units, I also asked to try their 545 Optical Disrupter. The 545 is a weird beast — part distortion effect, part compressor. (You may recall the name from my review of the DIYRE Colour platform, in which I discuss the XQP Colourupter, an Optical Disrupter in Colour kit form.) The 545 is a compressor, but its circuit causes asymmetrical compression that distorts low frequencies. It doesn't clip the source, but it's intended to be used as a distortion effect. The controls are simple: knobs for "Disruption" and makeup gain; an LED whose brightness indicates how hard the compressor is working (in a YouTube interview, XQP's A. J. Wells says that putting a gain-reduction meter on this unit would be like putting a gain-reduction meter on a guitar amplifier); and a "×4" button which makes the sidechain more sensitive, for quiet input signals or over-the-top crushing. 

My first instinct was to try the 545 on drums, in particular on a room mic. In this application, I typically want to squash the main drum resonances without cymbals ruining everything. The 545 does this really well. So well, that I actually ended up buying my 545 demo unit and a second one pretty much for stereo drum room mics. I also tried using the 545 on a "drum crush" aux — send all the close mics to a mono fader, aggressively compressed. (A little usually goes a long way in the mix.) I engaged the ×4 button so I could crunch my sources pretty hard, and I liked the results. The kick, snare, and toms got stronger, but again with much less cymbal hash than I usually expect. For both drum applications, this reminded me a bit of the 1176 all-buttons-in trick but without the cymbal wash that always leaves me wondering how anybody uses an 1176 this way. The 545 does good stuff to bass guitar as well — nice and gritty. It eats some of the sub-bass frequencies but leaves the perception that it's still a bass guitar and all. For vocals, I found the 545 a mixed bag. On some singers, it just sounded bad, and other distortion tools worked much better; but on some singers, you could get a nice dirty vocal while leaving the esses mostly intact, even with a substantial high-frequency EQ boost before the 545

The 545 is cool. It's not your run-of-the-mill compressor at all, and I love it for that. It's exactly the kind of thing that's fun to have in analog-land, even if you do a lot of in-the-box work. 

All in all, the XQP 535 Program EQ and 545 Optical Disrupter are both novel, cool, 500-series modules. Right on! 

Tape Op is a bi-monthly magazine devoted to the art of record making.

Or Learn More