Photo by yimmy149Photo by yimmy149 

A while back I had the pleasure of attending a seminar given by Gavin Haverstick
of Haverstick Designs. The topic of the seminar was how to measure the acoustic issues of your room. He talked about various measurement techniques and devices.

All of this was very interesting, but the most fascinating part for me was during the question-and-answer section at the end. Someone in the audience asked Gavin to give his opinion on digital room correction.

Let me take a step back and explain what I mean by “digital room correction.” There are several products on the market now that can tune studio monitors to the room they are in. For example, if the room is causing a boost at 200 Hz, these products will use a digital EQ to attenuate 200 Hz. The end result is (ideally) a flat frequency response.

The way these products go about measuring the room is by using an omnidirectional measurement microphone to “listen” to the room while the system generates white or pink noise through the studio monitors. Since the generated noise has the same amount of energy (or volume) across the frequency spectrum, the system can then intelligently “hear” when certain frequencies are being either boosted or cut by the acoustics of the room.

There are three main products that come to mind that incorporate digital room correction:

  • JBL LSR 4300 and 6300 series of studio monitors – These are very nice studio monitors with room correction DSP built into the speakers themselves. They ship with a measurement microphone for tuning the room.
  • IK Multimedia ARC (Advanced Room Correction) System – This is a plug-in designed to be inserted on the master fader of your DAW, just before the audio is sent to the studio monitors. It ships with a measurement microphone, and it stores the room correction settings inside the plug-in itself.
  • KRK ERGO (Enhanced Room Geometry Optimization) – This is a hardware box designed to go between your audio interface and studio monitors. It employs the same basic principle as the other two options above, but it simply does so in a hardware box, rather than in the speakers themselves or as a plug-in.

The audience member who asked Gavin about room correction actually owns a pair of JBL LSRs, but he has no acoustic treatment in his home studio. He was basically wanting to know if he could “get away with” just using the room correction feature on the speakers without buying any acoustic treatment.

Two Parts of Acoustics

When talking about acoustically treating a room, we need to look at two different aspects of sound. You can’t focus on just one and negate the other. Likewise, correcting one won’t fix the other. Those two parts are the frequency domain and the time domain of sound.

Frequency Domain

This is the most obvious side of acoustics. We’re all searching for this fabled “flat frequency response.” We know that the size and shape of a room contributes significantly to the frequency response of the room. Ergo (forgive the pun), we must address those frequency issues by altering the frequency response at the source.

This is done with some sort of equalizer. In the past, engineers attempted to do this buy using some sort of graphic EQ. They would send the outputs of their mixing console through an EQ, which they tuned by ear, out to their studio monitors.

Today we have very accurate products, such as the once listed above. These digital products can EQ a signal with surgical accuracy, but is that enough?

Time Domain

Sound travels fairly slowly (as opposed to light). It only travels at around 1,130 feet per second. We’ve all experienced this. Two football players hit each other on the other side of the field, and you hear the sound of the collision slightly after you see it.

While it’s not as obvious, the same thing happens in a studio environment. The sound leaves the speakers and bounces around the room. The problem is this. To accurately hear studio monitors, you need to hear them by themselves, without any reflections from the room.

This is why manufacturers measure their speakers in an anechoic chamber, a room that allows for no reflections.

If we are in a large enough room, we can clearly hear the direct sound from the speakers and differentiate that from the delayed sound that is bouncing off of the back wall. However, in most home studios, the room is fairly small, and most reflections happen rather quickly.

Our brains aren’t capable of distinguishing between these early reflections and the direct sound from the monitors. In fact, according to Gavin, any sound that reaches our ears within 50-80 milliseconds of the original sound gets interpreted by our brain as the original sound.

For example, if you have your studio monitors in front of you, and you play a snare drum through them, you’ll first hear the direct sound of the snare. A few milliseconds later your ears will hear the sound after it bounces off the walls to your left and right and also the ceiling above you. Since the walls and ceiling are fairly close, your brain will combine these early reflections with the original sound.

The result? Well, let me ask you this. What if you took a snare track in Pro Tools, duplicated it, and delayed the second track by a few milliseconds. What would you hear? The two tracks would be out of phase with one another. Whenever signals are out of phase, all sorts of issues occur, such as comb filtering (where certain frequencies get cancelled out).

The difference in sound will be rather subtle, but imagine this difference across an entire mix! All those frequencies will be reaching your ear at slightly different times. The result? A very fuzzy mix with little detail.

Conclusion

The problem with digital room correction is that it only addresses the frequency domain. Depending on the room, they may do a rather good job. However, if your room is causing a 30 dB cut at 100 Hz, these digital systems won’t be able to fix this. Most of them can only boost the signal by something like 6 dB, which isn’t enough to cover the 30 dB lost by your room acoustics.

As far as the time domain goes, I think it’s obvious to note that no amount of EQ will fix this problem.

I’ve used both acoustic treatment and the IK Multimedia ARC system. My findings? I heard an immediate difference as soon as I put up some acoustic foam to the left and right of my speakers. The sound was instantly tighter and more defined. With ARC, there was a difference, but it wasn’t as dramatic.

The goal of this article is not to sway you from digital correction products. They can be a valuable tool in helping create an accurate mixing environment. I love the JBL LSR monitors. They sound amazing, even without any room correction. Digital room correction, when added to acoustic treatment, can be very effective. However, nothing…I repeat nothing…can replace the need for acoustic treatment.

Update: Gavin and I teamed up to create a training course all about acoustic treatment. Check it out here: www.UnderstandingYourRoom.com.

  • Scott Osterloh

    When using a hardware digital EQ what is the goal as far as the visual graft in correction

    • http://www.homestudiocorner.com Joe Gilder

      Sorry, Scott. I don’t really follow your question…

      • Scott Osterloh

        I mean when I’m looking at my digital graph how should it look when its corrected I have a Phonic i7600. Also the whole process of measuring the room ie signal chain I have a JBL MSC1 also with RMC but the software always gives me an error message and support was no help. Thanks for any help.

        • http://www.homestudiocorner.com Joe Gilder

          Sorry. I don’t think there’s an answer to your question. There’s no “one size fits all solution.”

          • Scott Osterloh

            Its really awesome that you reply. Whats the process to measure a room using a digital eq. I am going to put up some bass traps, some disfusers, and such before I measure. This eq can send pink noise. Do I bypass my mixer or go into a channel, do I bypass any processors on the main insert.

            • http://www.homestudiocorner.com Joe Gilder

              I’m sorry, Scott. I don’t know. I’ve never done it. I honestly don’t know how beneficial it will be if it’s not done by a professional with professional equipment.
              Also, I’m able to get really great-sounding mixes without ever doing it, so you should consider whether you’d be better off spending your time honing your skills.
              I compare it to a guitarist who’s always on a quest for the perfect guitar, so much so that he never actually plays guitar and isn’t very good at it.

  • Seb

    some DSP include time and frequency domain. However most specialists recommend using acoustic treatment first and then fine tune with a DSP add-one for low frequency problems. DSP alone (frequency and time domain) can be good only for low frequencies as long as peaks do not exceed 8-10 dB but this does not solve other problems (early reflexion, flutter echos etc)

    • http://www.homestudiocorner.com Joe Gilder

      Thanks Seb. Your’e totally right. As with all things audio, it’s generally a good idea to improve things in the analog world before trying to fix it in the digital world. In this example, that “analog” improvement is actual, physical acoustic treatment.

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  • Namin

    I think the KRK Ergo does correct in the TIME (Phase)DOMAIN along with Frequency Domain. Thats whats mentioned on their FAQ website.

  • Jimmy

    From what I’ve heard, the best option is a bit of both. The ARC stuff is supposed to really improve definition once a room is properly treated, adding clarity to the big improvements room treatment gives.

    • http://www.homestudiocorner.com Joe Gilder

      Yeah, that’s kinda where I land on it, too. Even a well-treated room will still have some issues, which is where some room correction software might be ideal. But to use ONLY room correction software and no treatment, that to me is a bit unrealistic to expect good results.

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  • DonB

    One more point. If you record in the same room as your monitors (typical home studio), no digital system can correct for the room sound you get with your mics. To me, the most compelling reason to treat the room is to have a pleasing (or dead) acoustic space for recording.

    • http://FRNKNSTN.com FRNKNSTN (Pavel Gitnik)

      Good point. I used to mix with no acoustic treatment in my home studio; just with KRK ERGO correction. The bass response definitely tightens up considerably when you run the sound through the ERGO, but now that I started recording in this space as well, it’s not enough. The mic will pick up the room and you can’t do anything about it.

      Besides, as a producer/engineer, having that “treated room” look gives off that professional vibe you want and commands that respect. First impressions can be everything when you’re working with vocalists/instrumentalists. It’s a reality. Use it to your advantage. Look sexy. Feel sexy. Make sexy recordings.

      And I would definitely recommend Joe’s acoustics seminar, or at least reading a few articles online, before buying treatment. This little project will cost $700+ for a simple bedroom, so spend the time before you spend the money.

      • http://www.homestudiocorner.com Joe Gilder

        Don’t discredit the sexy factor. We had customers when I worked at Sweetwater who would buy the big Control 24 control surface for Pro Tools and not even use it. They just wanted something that looked impressive.

  • DonB

    It would seem the obvious answer is to mix with headphones. No room involved!

    Although I mention cans in jest, if you do have a good pair of reference headphones it’s a good idea to check your mixes with them now and again to hear what differences there might be from what you hear in your monitors.

    By the way, some home theater receivers have digital room correction built in. (Mine included a mic.) Of course, it’s more for listening enhancement, not for critical listening. They also help even out less-than-stellar home theater speakers. (I say “help” not “fix.”)

  • http://www.studioequipment.ch Terry Nelson

    Good subject, Joe.

    One very important point, in my opinion, is that most (if not all) auto-align EQ (or speaker-processing)systems are what I call “X marks the spot”, i.e. they set up the adjustment for that one place in the room. This means that while the engineer is grooving away, the producer or someone else sitting a few feet away will be getting a totally different impression. Not a good situation.

    Small room acoustics are notoriously difficult but some good, basic acoustic treatment will go a long way towards making the room usable as a control room. My advice would be start with the acoustics and then if you really have a bee in your bonnet with auto-align, it could be the cherry on the icing.

    • http://www.homestudiocorner.com Joe Gilder

      I totally agree, Terry. It’s amazing how differently a mix can sound from just a slightly different position in the room.

    • Ali

      Hi Terry,
      Would you tell me more about “auto-align EQ systems”. Do you mean the Digital Room Compensation or it’s something else?

      • http://www.homestudiocorner.com Joe Gilder

        I assume that’s the same thing.

        • Ali

          thanks!

  • http://twitter.com/JCPedroza JC Pedroza

    “As far as the time domain goes, I think it’s obvious to note that no amount of EQ will fix this problem.”

    That’s not totally true. Since the EQ will affect the phase (unless it has a linear phase type) you can use it for phase alignment purposes. Chances are that it won’t be the optimal solution (only optimal on very specific scenarios), but it is possible that X amount of EQ will fix time domain problems.

    • http://www.homestudiocorner.com Joe Gilder

      What I’m referring to is thing like tangential modes, where the sound bounces around the room, causing various issues at various frequencies. Slapping some EQ on there won’t fix the inherent issues of the room.

  • BRad

    Hi Joe!

    Llongtime reader, first time poster

    I realize this is late in posting to this artie, oh well.

    I’m a live guy who dabbles in recording. I shudder at the auto ‘eq’ with single channel measurement systems since the first days that JBL came out with it on thier black box processor for the original eon system.

    A better approach is a dual channel measurement system such as Smaart or SIM (among others) which can identify both magnitude and phase issues, being (but not limited to) frequency response of the monitors, reflections in the room and how the room affects the listening experience.

    Another huge one is aligning multiple speakers (surrounds, subwoofer, etc) to be aligned and properly crossed over at the listening position, verifying absolute polarity in signal chains, verify equipment (does the response of your monitors match eachother? Is that mic you just bought off ebay pin 3 hot? Etc) as well as measuring and aligning sources together (such as seeing if you will have timing issues in stereo mic setups, see if polarity of mics on drums/perc need to be adjusted relative to overheads/room mics, or how many samples you need to delay that bass/guitar di to the mic on the cabinet/instrument.

    I know this post was just about treatment vs processing and this reply goes on a tangent on the early turn on the freeway …….

    • http://www.homestudiocorner.com Joe Gilder

      Tangents welcome. Thanks Brad!

  • James

    I agree that room correction is indispensable; but I want to see if my thinking is correct. If you put up a few pyramid foam panels (to eliminate echo/flutter) for the high end, couldn’t you use room correction to correct low end buildup/standing-waves?

    • http://www.homestudiocorner.com Joe Gilder

      The standing waves are still a result of the sound traveling around the room. For example, one of your problematic frequencies could be 100 Hz. That means at certain points in your room there’s a huge boost at 100 Hz, and at other points in the room there’s a huge cut. There’s not possible way to accommodate for this without acoustic treatment.

      For more detailed info, check out Understanding Your Room.

    • Antonio Freitas

      Hello James. In addition to Joe’s response, I hope I can further help you in making better choices on the treatment of your room. I built a project studio in the mid 80’s and modified it in the early 90’s. I was caught between a very tight budget and a lot of research I had done on acoustics and acoustic treatment, and I always needed to used some equalization (for my sweet mixing spot) to complement the treatment.
      This last year I have been back into the researching mode for the biggest bang for the money to further upgrade my studio. My recommendation is to stay away from the foam stuff. It is very popular, but not good enough for what you need or want (I also have some of the good ol’ Auralex). From my research, it appears that some of the claims of how much attenuation (sound absorption) the foam does, the testing is done in ways that are NEVER used within a project studio, which translates to the foam being less efficient in actual applications then what is claimed.
      My recommendation is for you to look at Rigid Fiberglass or Rock Wool panels (3” or so) and, if you can, mount then a couple of inches away from the wall. You will get a lot more out of them, since whatever sound travels through them and bounces off the wall will get further absorbed. These panels are known for a fairly even and very broad frequency taming, including the extremely problematic bass frequencies. I know that most rooms are small and this will rob a substantial amount of room volume, but if you can afford both the loss of volume and the expense this is the way to go. Keep in mind the possible use of diffusers for the back wall
      Good hunting and good luck!

      • http://www.homestudiocorner.com Joe Gilder

        Foam certainly isn’t the best case scenario. A thicker material will generally absorb down to lower frequencies. You can never have too much bass trapping. That said, I like the foam in combination with bass traps.

  • EltonLG

    Hello Joe! A real acoustic treatment is the best solution, of course. But do you know Audyssey technology? My HT receiver has it and it does a fantastic job correcting the acoustics in the frequency domain AND time domain. Please take a look at http://www.audyssey.com/technology/multeq/graphs/graph1.html and tell us what you think! Thanks.