I jumped at the chance to audition the DocDerr EQ/compressor, a new 500-series module designed by ELI’s founder/designer Dave Derr. I, along with almost everyone else in the audio world, am a huge fan of his Distressor compressor, so my interest is always piqued when a new product of his is unveiled.

My first impression of the DocDerr was a bit strange, to be honest. For one, there is no obvious visual indication that the unit is a compressor as well as an EQ. The compact, busy faceplate is fully tattooed with settings and markings, and it houses an eye-popping 23 LEDs, some of which are, upon closer inspection, for gain-reduction metering. There are five knobs, labeled from top to bottom (on the vertical version) IN, LF, MF, HF, and Mix. The central three knobs are clearly EQ cut/boost controls, albeit topsy-turvy from the normal low-to-high orientation (it makes more sense in the horizontal version), but the top and bottom compressor knobs are a little less obvious (I’ll describe them in a minute). The only other controls are three white conical pushbutton switches, which provide relatively extensive digital control over the analog processing of the DocDerr.

As for the EQ controls, you can activate a low-pass filter by pushing the top two buttons together, scrolling through the three settings (off, 70 Hz, 100 Hz). Each of the other three EQ bands has a selectable center frequency, chosen out of seven options (per band) by depressing the corresponding button until the desired frequency is indicated. (You can also hold down the knob for the frequency selection to cycle backwards.) The LF band goes from 80 Hz to 500 Hz, the MF band from 250 Hz to 4 kHz, and the HF band from 3.5 kHz to 15 kHz. You can sharpen the Q of the MF band by depressing the bottom two buttons together, which is handy for pinpointing troublesome midrange frequencies. I’d like to see lower frequencies on the LF band, since I’m often interested in boosting bass drums and bass guitar down in the sub area, from 30–50 Hz. My only other gripe about the EQ is that there is no way to bypass it. Otherwise, I found it a highly effective, very smooth equalizer, especially in the upper midrange and 10–15 kHz range. High amounts of boost rarely felt phase-shifty or overly harsh. It A/B’ed very favorably to the API 550A EQ, even though they are very different operationally, the 550A having different center frequency points and stepped gain versus the DocDerr’s continuously variable 14 dB of boost/cut.

The compressor circuit has only two controls — the aforementioned IN and Mix. The ratio and time constants are fixed, so your only decisions to make are how hard to drive the compressor (i.e., how much gain reduction you want) and how much of the compressed signal you want to blend in with your uncompressed, EQ'ed signal. After getting used to the lack of controls that are standard on other dynamics processors, I started to get really into the simplicity of it; I found it super-effective at leveling out dynamic vocal and guitar performances, allowing the voice or instrument to assert itself aggressively in the mix without being peaky or pokey. The Mix control is essential to find the sweet spot where the compressor is doing its job without being audible as an effect - unless you want it to be, of course. For instance, on close drum mics, I generally favored 6-9 dB of gain reduction, with a 50-60% wet blend; whereas on room mics, I was dialing in slightly more gain reduction and higher blend percentage, to really make the ambience of the room pop. Be aware that since there's no make-up gain, you may need another gain stage following the DocDerr (like a fader on a console) if you run the Mix control high. 

The manual claims that the DocDerr’s design came out of the quest for a live acoustic instrument preamp/processor, so the DocDerr accordingly ships with a female 1/4’’ to male XLR adapter cable, enabling you to plug a guitar or bass directly into the back of your 500-series rack. Also, there is an internal jumper setting to increase the input impedance while also adding 16 dB of gain. I found this an effective way to sweeten up a DI signal, provided your musician is close enough to your rack to plug right into it. In this scenario, bypassing the compressor to achieve parallel tape saturation emulation makes a huge difference, giving the extra juice a direct signal often needs to work in a mix. This is the most secret control on the DocDerr, not referred to anywhere on the faceplate; you depress the top and bottom buttons simultaneously to bypass the compressor, turning the IN/Mix knob combo into a saturation/distortion generator.

One last thing worth mentioning is, ironically, the first thing that I noticed after plugging it in. In normal “differential” mode, the DocDerr adds 6–7 dB of gain to your signal, although you can pop it out and change a jumper to make it “single-ended” in order to work at unity gain if you’d like. This level boost, plus the lack of a bypass switch, makes it a little tricky to A/B what your EQ settings are doing, but at least you can disable it. Also, I did find that if I wasn’t using the compression circuit, I could put the Mix knob to 4.5, blending it with silence and thereby turning down the EQ’ed signal to roughly unity.

The overall sound of the DocDerr is definitely top shelf, even if some of the controls and layout are a bit unfamiliar to the average engineer. I don’t want to imply that the DocDerr is hard to use, however; after a perusal of the manual and ten minutes playing with it, you learn its quirks and get a pretty solid sense of how to operate the thing, and how to get the fullest use out of it on a given source. Even though I sometimes wanted more control over the output level, or felt like I had to work a bit to find the sweet spot of the compression circuit, I was always really happy with my sounds going through it. The price is extremely fair for a processor that does this much this well. If you don’t have a 500-series rack already, or are out of space in yours, the Empirical Labs EL500 2-space rack provides high-spec power and versatile I/O to the DocDerr or other 500-series modules, complete with a front-panel instrument input and a linking function built in. As already mentioned, the DocDerr is also available in a horizontal configuration for the EL500 or other 1RU frames. ($799 street; www.empiricallabs.com)

–Eli Crews, www.elicrews.com


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