Clean Up Your Room - Part 1: Digital Room Correction

June 15, 2012

 
 www.endoverendstudios.com
EVER WONDER WHY YOUR MIXES—WHICH SOUND SO GOOD IN YOUR HOME studio—sound like muddy swill when you play them back somewhere else? Where’s the beef? What happened to the definition in the high end? Why did that big stereo image collapse into sounding like it’s inside the cardboard box your studio monitors came in?

The Problem

The answer is that no matter how painstaking your recording process, and no matter how great your mics, preamps, converters, synths, and monitor speakers, the mix can only be as good as the decisions you make based on what you hear. In turn, what you hear is affected by what your room does to the sound.

Unless your space was purpose-built for acoustic accuracy, that’s usually not good. Decisions that sound right enough in your studio—say, how much low end you put in the bass track or how widely you panned that stereo synth—won’t necessarily translate well to car stereos, headphones, and other environments.

The sonic culprits are many, and without turning this into an acoustics lecture, there are two approaches to the problem. You can pre-emptively tweak what’s coming out of your speakers to compensate for how your room is about to mess it up, and/or you can address the room physically. The former is room correction: technology that analyzes the “as-is” frequency spectrum in your space, then applies corrective EQ. The latter is room treatment, and can involve bass traps, acoustic foam, diffusers, speaker isolation pads, and other such materials.

Most real-world creative spaces are problematic enough that some combination of both is ideal. In this issue, we’ll examine digital room correction systems from IK Multimedia, KRK, and JBL. Next month, we’ll look at strategies for using the broad range of room treatment panels and products on the market.

IK Multimedia Advanced Room Correction (ARC)

$349.99 list | $199.99 street | ikmultimedia.com

 
IK ARC’s measurement mic and room analysis screen.
Like all solutions in this roundup, IK’s ARC includes an omnidirectional condenser mic for sampling your room and standalone room analysis software. What sets ARC apart is that other than the mic, it uses no dedicated hardware. You insert a plug-in on the master stereo output of your DAW, and based on the room analysis, it corrects the audio as you mix. When done mixing, you turn the plug-in off before bouncing to disk or summing to your stereo medium of choice.

Calibrating ARC is simple. Plug into a mic input on your interface and point the mic skyward on a stand. After performing a few simple level adjustments, you’re ready to sample your room.

Naturally, you want the mic to listen from the same spot you do, but ARC aims for a broader sweet spot. You start by placing the mic at ear level, in the center of your optimum seated position between your monitors, and then at random spots nearby. Th e software sends audio impulses from the left speaker, then from the right. You must take at least a dozen samples before you can store an analysis, but IK encourages 16 or more. I took 20 samples, loosely describing a concentric, elliptical area around my listening post on my first pass, and 30 on a second, wider sweep.

The plug-in window shows color-coded contrast between untreated audio, a target correction, and the actual frequency response post-correction. From this, it was easy to tell that my room needed help with dips at 70 to 100Hz. ARC’s corrections were less drastic on the left channel, likely due to the placement of my manual-packed bookshelf, which absorbed low-end distortions caused by standing waves. A couple of spikes existed around 200 and 220Hz, and again, this was more pronounced in the right channel—which made a strong case for moving my whole setup leftward for better symmetry between channels.

Different EQ curve presets are mostly useful for auditory perspective, but you can also use them to roll off highs and mids in rooms that may overemphasize those frequencies. As always, play some of your favorite mixes through the plug-in to arrive at a setting that works best for you. After A/B comparisons on the same material, mixes through the second analysis had more detail across the frequency spectrum, more discrete imaging, a better-defined low end, and clear transients—so clear, in fact, that the annoyingly uniform picking transients on a sampled guitar sent me back to my sample libraries in search of a new instrument. That’s the kind of thing I otherwise might not have caught until I’d finished a mix and was listening outside my studio.

Because ARC relies on just two software components and the provided mic, it’s the most mobile compared to the KRK and JBL products, which use proprietary interface and control surface hardware in addition to a mic. Additionally, you can save as many analysis files as you’d like, which is ideal if you work in different rooms.

Just as we went to press, we learned IK was about to release a new version, ARC System 2. Though we haven’t tested it yet, we know it increases the number of EQ bands fourfold (tightening the bandwidth of each to 10Hz, compared to the current 40Hz) and promises to require fewer measurements to produce an accurate analysis.

KRK ERGO

$799 list | $499 street | krksys.com

 
KRK’s system stores its room profiles
in the hardware. The only software is a control panel for its audio interface functions—there’s no plug-in or graphical EQ curves to deal with.
ERGO stands for Enhanced Room Geometry Optimization. Home studios tend to be squares or rectangles, and sound waves bounce off parallel walls, boosting or reducing reflected frequencies. Because of the nature of low frequency waveforms, which need more physical space to develop than higher ones, they can lose focus, especially in small rooms.

ERGO operates on the premise that the most troublesome frequencies dwell from 20 to 500Hz. KRK claims that their room correction is “almost insensitive to broadband background noise.” The fact that I achieved virtually the same calibration results during a period of heavy outdoor traffic and during quiet, early morning hours tends to bear their claim out, making ERGO ideal if you don’t have a space that’s sonically isloated from the outside world. ERGO works well with any studio monitors, not just those made by KRK.

KRK includes a proprietary measurement mic (it uses 15 volts for phantom power, not the usual 48) as well as a 24-bit/96kHz FireWire 400 audio interface and a four-pin adapter to fit the port many laptops use. (USB would be a better call for a future version, given trends in consumer electronics.) ERGO saves its room analysis data in the hardware unit, and you’re limited to analysis for each of two monitor systems. You can always overwrite the memory if you need to record in a different room, but as the analysis can take nearly half an hour, it would be handy to be able to store more data files offline. It would also be a plus if, like the other packages, ERGO produced a visual graph of its findings.

ERGO gathers its data starting with the engineer’s ear-level perspective. You then do a number of sweeps of your room from random vantage points, until the system acquires what KRK calls “room knowledge.” Whereas ARC required a close, elliptical pattern of measurement spots, KRK encourages mic placement anywhere. The result is a pair of data files: one representing the near-field position, and another with a much broader sweet spot. A button switches between the tight focus, the broader image, and bypass. The broad (called Global) image is useful if you have clients in the room, but I’d stick with the focused one for a critical mix.

The dedicated hardware lets ERGO double as a monitor control module; you can hook up either a 2.1 system or two stereo pairs. If your recording needs are relatively simple, you can use it as your main audio interface: You get a couple of line-level 1/4" inputs, and that’s about it. You can also can pipe your main interface through the ERGO’s S/PDIF digital audio input and enjoy its room correction capabilities. The system has balanced 1/4" line outputs for your active monitors or studio power amp. I’d have preferred XLR outs as well, but still, this is one clean, sweet-sounding interface.

As promised, the bottom end of my mixes went from boomy to tight, with more focused bass; punchier, balanced kick drums; and even improved definition for pad parts and drones dwelling in the lower frequencies. Mixes translated nicely between studio, home hi-fi system, and car stereo.

JBL MSC1

$375 list | $299 street | jblpro.com

 
The JBL hardware (left) and software console (right), showing a graph of the author’s room response.
MSC stands for Monitor System Controller, and indeed, JBL’s offering is both a room corrector and a monitor volume control/switcher that can handle two pairs of speakers, a subwoofer, and three input sources: two on 1/4" balanced ins and one (such as an iPod) on unbalanced RCA jacks. For our purposes, the relevant acronym is RMC: Room Mode Correction. MSC1 aims to isolate any issues typically in the low frequency range of your room, and applies customized filters based on its findings. Of the three packages, the JBL system’s room analysis process is inarguably the most detailed—and the most complicated. JBL supplies a proprietary calibration mic and the requisite cabling.

The USB port is only for talking to the included MSC software—unlike the KRK ERGO, the JBL is not an audio interface itself. For that reason, room analysis requires a specific wiring setup whose oddest routing is from the headphone out on your audio interface to the RCA ins on the MSC1 box—this is the only path taken by the test tones used for room analysis. We get it— JBL is being inclusive of audio interfaces (and internal sound cards) that may have only stereo main outs plus a headphone jack. You don’t have to leave it this way when mixing through RMC, only when performing the analysis itself.

Setting out to do just this, I heard fluctuating low-level noise, which sent me around the room chasing the cause. Not surprisingly, the wiggle factor of the cabling I’d cobbled together for the required routing (1/4"-to-1/8" adaptor plug in the headphone jack of my MOTU 896 interface, then 1/8"-to-stereo-RCA Y cable) was to blame. The measurement mic also connects to the MSC1 via a 1/8" jack. Balanced I/O and pro connectors for the test tone path and mic would add cost, but would resolve such issues.

The MSC1 software uses animated diagrams to walk you through the multiple setup stages. The first of these is a preliminary calibration of your system, including your audio interface. This involved reconfiguring audio I/O in order to analyze the inner workings of my MOTU 896. The process was a bit fiddly, but fortunately, you don’t have to repeat this part of it unless you change audio interfaces. Once completed, you set up gain-staging between your interface, mic input, and speaker output. Only then are you ready to “shoot the room.” There are a few variables, including the mic input gain knob on your interface; the MSC1 itself provides a large volume knob and and input trim.

Now, set the mic at ear level, click the start button, and get out of the way quickly and quietly—I had five seconds before my speakers produced a raft of organ-like tones. Th e MSC1 performs just one sweep consisting of a series of tones from left and right monitors. This takes about ten minutes per side, but unlike the other products, doesn’t involve moving the mic around the room.

The MSC1 software won’t complete the calibration without peace and quiet; even a little noise returns you to the gain-staging phase. My studio has a window facing a well-traveled street, which necessitated moving my test sessions to late evening. When things were perfectly quiet I tried again, but gain-staging that made the software happy still took some time to get right.

I found the now familiar low-end problems in the 70-to-100Hz range; my room is what it is. The results were similar to my measurement with the other systems, with the MSC1’s added benefit of sweepable EQ for lows and highs. (For midrange to upper frequencies, you get a plus or minus 3dB shelving EQ ranging from 2.5 to 17kHz.)

Conclusions

None of the products we’ve auditioned are magic fixes; you’lll still have to EQ, compress, adjust levels, pan … you know, mix. Room correction simply helps you make better decisions. If you’ve followed the room analysis procedures to the letter, any of the above products will dramatically reduce bass issues and frequency response problems endemic to tight spaces with parallel walls. The EQ-based nature of room correction, though, may not resolve other issues such as flutter, ringing, or coupling between your monitors and the desk they’re on. We’ll discuss physical room treatment next month, as well as integrating the digital and physical approaches. See you then!

Focusrite VRM

To quote The Shining, one way to “correct” a room is to eliminate it. That may not be the primary purpose of Focusrite’s VRM (Virtual Reference Monitor) Box, but it’s cerainly a benefi t of this nifty little D-to-A converter/ headphone amp/speaker simulator. You can place any of 15 pairs of virtual speakers (including KRK, ADAM, and Yamaha NS-10) in one of three spaces (studio, living room, or bedroom), and immediately hear the effects on your mix. Whatever lab-coat geekery Focusrite put into the modeling pays off: I experienced fewer stereo placement issues that I normally do when mixing on headphones. For our purposes here, the simulations’ accuracy is less important than their diversity: The more of them you get your mix sounding good through, the better it will translate outside your studio. Obviously, you want accurate headphones. I’ve been using Audio-Technica ATH-M5Os with good results.
Stephen Fortner

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