Published On: November 18, 2013

Automated Room Correction Explained

Published On: November 18, 2013
Last Updated on: October 31, 2020
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Automated Room Correction Explained

Today's AV receivers can do everything from take 10 HDMI inputs to connect to the Internet, as well as make you a squeaky-dry martini. Room correction is a compelling feature on most of today's best AV receivers, but getting "better" sound thanks to your automated room correction isn't a cake walk. Dennis Burger walks you through the process for nearly every receiver and correction process in the market.

Automated Room Correction Explained

By Author: Dennis Burger

Dennis Burger is a native Alabamian whose passion for AV began sometime before the age of seven, when he dismantled his parents' brand new 25-inch solid-state Zenith console TV and exclaimed--to the amusement of no one except the delivery guy--that it was missing all of its vacuum tubes. He has since contributed to Home Theater Magazine, Wirecutter, Cineluxe, Electronic House, and more. His specialties include high-end audio, home theater receivers, advanced home automation, and video codecs.

Anthem-Receiver.gifIf you've purchased a new AV receiver or surround sound processor in the past seven or eight years, chances are good that it included some form of auto setup and/or automatic EQ (also known as room correction.) On the surface, all of the different auto-calibration systems - from Audyssey to ARC to MCACC to YPAO - seem similar in implementation. Each requires you to place a microphone in your room (either in your main listening position or at several points in the room, depending on the sophistication of the system), which measures test tones played through each of your speakers, then uses those measurements for two different purposes. Firstly, the software will automatically adjust the relative levels of all your speakers, so that the center, mains, surrounds, and subwoofer are all playing at the same loudness. It sets the crossover point between your satellite speakers and subwoofer, and it makes an educated guess as to how far each of your speakers is from your main listening position and adjusts the delay settings in your receiver or processor accordingly. Secondly, it looks at those measurements to determine what sort of deleterious effects your room's acoustics are having on the performance of your speakers, and then applies some mixture of equalization and/or filtering to compensate.

It's worth noting, though, that no amount of digital room correction can compensate for all of the acoustic problems in a room. To understand why, we need to break the audio spectrum into two different chunks and look at them separately (with apologies in advance to any acoustic experts in the audience for the oversimplification that follows). From 20 Hz to somewhere around 200 or 300 Hz, standing waves are your biggest enemy. Standing waves are an unavoidable byproduct of placing loudspeakers in an enclosed space. The reflected sound waves from your walls interfere with the sound waves coming directly from your subwoofer or speakers, resulting in an increase in volume at some spots in the room and a decrease in volume at other spots, with different dips and spikes at different spots depending on the frequency. In other words, even if your subwoofer is creating low-frequency sounds at the same loudness level across the entire bass spectrum, a 50Hz tone may be twice as loud in your listening position as it's supposed to be, whereas an 80Hz tone may be practically nonexistent. Switch to another seat in the room, and the opposite may be true (probably not exactly, but you get the point). And all of this is determined primarily by the size and shape of your room, as well as where the speakers are placed.

Room-Correction-Graph.gifStanding waves are also really tough (if not impossible) to combat with physical acoustic treatments alone, which makes digital room correction an ideal solution. Well, it's an ideal solution to at least half of that problem. While equalization can handily deal with nasty boosts in bass caused by standing waves, most room correction systems cannot effectively deal with dips in bass caused by interference. In other words, if the size and shape of your room are causing, say, 80Hz tones to fall into a black hole at your favorite seat in the room, digital room correction isn't really your best bet for solving the problem. You're much better off moving your subwoofer, rearranging your furniture, or adding another subwoofer to your system - not to generate more bass, but to give you more even bass coverage, with one sub filling the nulls caused by the placement of the other. But, when it comes to combating the boomy, bloated bass caused by the reinforcement of standing waves, most room correction systems can work wonders.

Above 200 or 300 Hz or so, though, your room's effects on the sound that reaches your ear have less to do with the size and shape of the space and more to do with the qualities of the surfaces within it. Here, we're dipping into controversial territory, because not everyone agrees that a digital room correction system based on microphone measurements and calculated target equalization curves can successfully deal with problems in these frequencies. As acoustic engineer and president of Performance Media Industries Anthony Grimani once explained to me, "An omnidirectional microphone does not listen the way a human being does. The main difference is that a human being hears high-frequency sounds as mainly directional, directly from the speaker, and low-frequency sounds as integrated from the speaker plus the room. And then between low-frequency and high-frequency, there's a splice where those different ways of hearing gradually shift from one to the other." Needless to say, a microphone doesn't hear things that way.

Acoustic experts ranging from acoustic consultant Floyd Toole to Pro Audio Technology founder Paul Hales agree that room correction shouldn't be applied above this switchover point, primarily because our brains are perfectly capable of compensating for things like the difference between direct and reflected sound above 200 or 300 Hz. The way Hales explains it is that a great concert grand piano sounds like a great concert grand piano no matter where you put it; you don't EQ it differently for different rooms. Likewise, whether you and I are talking in an anechoic chamber or a tiled public bathroom, you recognize my voice as being my voice. That's why many of us who aren't overly enthusiastic about many digital room correction systems describe the results as deadening or dull.

Meyer-SIM-Graph.gifThat said, I'll be the first to admit that better digital room correction systems - those with a higher filter resolution and those that measure not only the relative loudness of different frequencies, but also when those frequencies arrive at the microphone - can do a good job of combating some acoustic problems in the higher frequencies. They can't effectively deal with things like long reverberation decay, at least not in my experience with setting up home theater systems for friends with very reverberant rooms. If you play guitar, you're probably well aware of the effect that a long decay can have on sound. If not, sit in your room and sing a few notes. If your voice sort of hangs in the air for a bit, what you're hearing is long decay. Or you can stand in the middle of your room and clap your hands. If it sounds like you're in a cathedral or parking deck, no amount of digital room correction can effectively compensate for that. You're going to need to invest in some absorptive acoustic treatments for your room, whether they be professional products or just some strategically placed draperies.

Good digital room correction can, though, combat ringing artifacts (a bit of pre-echo or post-echo accompanying high-frequency sounds). Of course, not al
l digital room correction systems are the same, and not all of them deal with different acoustic artifacts in the same way. So it's worth discussing a few of the more popular (as well as a few of the more advanced) room correction systems individually. This isn't a comprehensive list by any means; the intent is merely to give you a selective overview of the different room correction systems you're likely to come across when shopping for a new receiver or AV processor.

Dennis looks at every type of room correction, brand by brand on Page 2

The big daddy. The Godfather of mass-market room correction systems. The first name you think of when you think "auto-EQ." Audyssey's room equalization platform appears in everything from Denon's $400 AV receivers to Wisdom Audio's $6,000 SC-1 System Controller. Of course, both ends of that spectrum aren't covered by exactly the same Audyssey technology. The company's auto-equalization is available in five different flavors, starting with its basic 2EQ solution. You may recall from my review of Cambridge Audio's Azur 751R AV Receiver that I'm not overly fond of 2EQ, which completely ignores the bass frequencies that most benefit from digital room correction and features a limited number of filters for high frequencies.

The standard MultEQ solution improves things a bit, with twice the number of high-frequency filters and some much-needed correction for bass frequencies. But with all due respect to Audyssey, in my experience, I still find that MultEQ does more harm than good to the mid and high frequencies in anything approaching an acoustically acceptable room.

Move up to MultEQ XT, though, and now we're talking. With eight times the high-frequency filter resolution of vanilla MultEQ, XT allows for more precise equalization and, as such, sounds less processed, less lifeless, more spacious. It also allows for eight measuring positions (compared with MultEQ's six and 2EQ's three). More measuring positions means that the system has a more comprehensive view of your entire listening space, allowing it to make more intelligent decisions about which problems it should and shouldn't try to correct. When reviewing a receiver with MultEQ XT, I tend to turn it off when listening to multi-channel music, but I quite enjoy the effect it has on movies.

For most consumers, the step-up MultEQ XT 32 - usually only included with top-of-the-line receivers - is as good as it gets, with 256 times the high-frequency filter resolution of MultEQ and four times the bass filter resolution. Like MultEQ XT, it also benefits from eight measuring positions and, also like MultEQ XT, it gives professional installers access to MultEQ Pro, a kit that includes a professional-grade microphone and preamp, and allows for as many as 32 measurements in the room. MultEQ Pro also allows your installer to dial in customized target EQ curves better suited to your listening environment and preferences, rather than the one-size-fits-all target EQ curves of 2EQ, MultEQ, XT, and XT 32.

Chances are good that, if you buy a mass-market receiver above the entry level that doesn't feature Audyssey, it will instead include one of two proprietary alternatives. MCACC (or Advanced MCACC) is Pioneer's room correction system, and it has improved dramatically in the past few years. MCACC is nice, in my opinion, in that it gives you a lot of visual feedback for things like the amount of reverberation in your room. Depending on the model of Pioneer receiver you opt for, you'll have either five or nine bands of parametric equalization at your disposal and, from my experience - with a bit of tweaking - overall performance is on par with Audyssey MultEQ XT (despite the fact that the systems operate quite differently).

Yamaha-rxv775_rear.gifYPAO (Yamaha Parametric Room Acoustic Optimizer)

YPAO, as you may have guessed from its name, is Yamaha's proprietary room setup system. Unlike other manufacturers, the company doesn't give different names to its different levels of implementation, but YPAO on high-end Yamaha receivers doesn't sound like YPAO on its budget offerings. I will say this, though: I like YPAO a bit better than Audyssey's MultEQ (and especially 2EQ), mostly because it doesn't do much. That may sound like a backhanded compliment, but I appreciate the fact that YAPO doesn't color the high end nearly as much. Unfortunately, as an auto-setup program, Yamaha's offering can be rather lacking. The system has never set crossover points, speaker size, or subwoofer levels correctly for me. So, if you're running YPAO, prepare to tweak pretty much every one of its default settings by hand after the fact. That's true to some degree of many auto-setup routines, but it's universally true with YPAO.

Anthem Room Correction
Anthem's proprietary room correction system is, in my opinion, the best of the bunch, although it is limited to Anthem's pre/pros and receivers. Unlike most room correction systems, it does require the use of a Windows computer, and the microphone that comes with ARC is a beast compared with the little hat-wearing hockey-puck mics packed in with most room correction systems. The use of a computer provides ARC with much more processing power to take its measurements and create its filters. Perhaps due to that fact, ARC has never failed to perfectly nail crossover points and speaker levels in the dozens of times I've run it on both my D2v 3D processor and MRX 700 receiver. [Editor's note, 11/20/13: A previous version of this story suggested that ARC does speaker distance measurements, but it does not.]

What I really love about ARC, though, is that by default it doesn't apply correction to any frequencies above 5,000 Hz, and it allows you to set the max EQ frequency yourself, at anywhere between 200 and 5,000 Hz. In my main home theater, with the Anthem D2v 3D, I tend to find that a max EQ setting of roughly 400 Hz is ideal. In my secondary home theater in the back of the house, I set the MRX 700's max EQ to 600 Hz so that the system can smoothly deal with a spike in that room at right around 500 Hz.

It should also be noted that, until now, Anthem hasn't given ARC different names for different levels. If you ran ARC on the D2v, it ran at its full capabilities; running ARC on the MRX 500 or 700 gave you the same measurements, but applied fewer filters. ARC also required that the connection between your PC and pre/pro or receiver come in the form of an RS-232 connection, which required the use of a USB-to-serial adapter for most users. With the introduction of the new MRX 510 and 710 receivers, Anthem also debuted ARC M1, which benefits from more filters for the receivers (not as many as the D2v is capable of, but still more), along with speedier calibration and network capabilities. So now you'll be able to run ARC on a new Anthem receiver as long as it and your computer are both connected to the same home network.

Paradigm/Anthem also has another proprietary room correction system called the Perfect Bass Kit, which as you may have gathered only works on Paradigm subs. Think of it as a simplified version of ARC (with simplified connections, too; it includes the same USB microphone as ARC and only requires a USB connection from your computer to the subwoofer). The great thing about PBK is that it applies room correction where your room needs it the most - in the bass frequencies. The downside, of course, is that this only applies to the subwoofer channel, which is probably crossed over at 80 Hz by your processor. So it won't catch problems in the main channels, which also generate bass between the crossover frequency and that critical 200-to-300 Hz point where standing waves can plague upper bass performance.

Sunfire Room EQ
Sunfire doesn't have a fancy name for the room EQ system included with many of its subwoofers (I've run it with excellent results on both the AtmosXT in my bedroom and the SubRosa Flat Panel Subwoofer in my home theater). It's quick. It's simple. It gets the job done and deals with most of the acoustic problems in both of my rooms. But of course, as with PBK, it can only apply correction up to the crossover point between your subs and satellites.

Before the advent of Audyssey Dynamic EQ, TacT was the only digital room correction system I had any experience with that adjusted its filters based on your listening level. Until recently, TacT room correction was also limited to the company's own preamps and room correction processors, but it will soon be available in Emotiva's new XMC-1 pre/pro.

Trinnov calls its room correction system Acoustic Correction, and by all rights I should hate it. Uniquely, Trinnov works not only in the frequency and time domains, but in the spatial domain as well. The microphone included with Trinnov is actually a microphone array that includes an arrow that must be pointed directly at your screen. During its measurements, the system maps your speakers' locations in three dimensions and can actually move the perceived location of one or more of your speakers to compensate for less-than-ideal speaker placement. It can take front left and right speakers that are spaced too closely together - or too far apart - and virtually relocate them to a pitch perfect 22.5 or 30 degrees out from your center channel. It can even bring the image of your center speaker up to the level of your main left and right speakers if it's placed too far below (or, heaven forbid, above) your TV. The effect is downright spooky, and again - on paper - I absolutely hate the idea of it. But in practice, it's fantastic. I reviewed a Sherwood Newcastle receiver a few years back that included the Trinnov Optimizer and absolutely fell in love with the effect. If the realities of your room prevent you from placing your surround channels symmetrically, or if your room itself is oddly shaped, I highly recommend giving Trinnov Acoustic Correction a try.

Of course, as I said, this list overlooks many other notable room correction systems, from Harman's ARCOS to Lyngdorf's RoomPerfect to Meridian's excellent MRC, along with other bass-only solutions like Velodyne's SMS-1. So, if I've left out your favorite, let us know in the Comments below.

Do you love what room correction does for your sound system, or do you absolutely loathe it? Or does your relationship with room correction, like mine, fall under the fabled Facebook category of "It's Complicated"?

  • Franco
    2017-06-09 20:26:48

    Great informative read for the lay person, thank you!

  • Norman Varney
    2014-02-07 14:20:28

    Electronically altering the electronic signal feeding the speakers is not the same thing as altering the acoustic sound waves in the room. The difference between the two is important and sometimes misconstrued.

  • gadgety
    2014-02-07 12:40:48

    "They do nothing to sound waves." Sorry for this necro, but I saw this absolutely ludicrous comment that should't go uncontested. If room correction did nothing to soundwaves, sound wouldn't change. The effect of room correction is based on measurements. We've used two Tact RCS preamps and measured the correction effect of the first with the second system microphone, and it is extremely measurable. Your ears can also tell the difference.

  • Dennis Burger
    2013-12-06 15:49:53

    Hey David, Sorry I didn't reply before now. I'm actually working as we speak on my review of the MRX 710, and I'll do my best to answer that exact question in detail -- with graphs -- in the review. Stay tuned!

  • jerrydel
    2013-11-20 23:29:53

    The other way to prove the worth of a good installer is to show a client say a Crestron done by a LOUSY installer. That works too!!! :)

  • Dennis Burger
    2013-11-20 15:51:02

    Morgan, Audyssey tends to be very tight-lipped about exactly how its system works (e.g., not revealing exactly how many finite impulse response filters its various incarnations uses, preferring instead to say that each iteration offers X more filters than the one before it). But as best I can figure given what I know about room correction, what Audyssey is doing when you take multiple measurements is making intelligent decisions about which problems to correct and which to leave alone. So, let's say for example that your seat has pretty even bass response, but if you move three feet in front of your seat, there is particularly nasty room mode. If it sees that mode appear in several measurements, I assume it's more likely to correct for it. And if you tend to have people sitting in that location, you probably want it to.

  • Alain Bourelle
    2013-11-20 15:48:13

    You got it right Dennis. Not all are created the same and ARC M1 is possibly the best of the bunch. I have been in the A/V business for 10 years and seen (and used) many different ones. I purchased an MRX710 1 month ago to replace an MRX500 and i am very pleased with the result of ARC. It does not do speaker distances but does everything else right. I also have 2 Paradigm subs with PBK and the combination is just perfect. Don't be afraid to fine tune your settings to your liking though.

  • Dennis Burger
    2013-11-20 15:40:40

    Ack! Jack, you're absolutely correct. My fingers went on auto-pilot there. (Well, there's also the fact that my speaker distances hardly ever change, even when I install new speakers, so it's been many a year since I had to adjust that setting.) I'll see if I can get that corrected. Thanks for noticing the oversight!

  • Norman Varney
    2013-11-20 14:20:49

    Great article Dennis! I find these types of devices most beneficial for compensations of the source and/or the receiver, however they are most needed for the mass market, who set up their systems haphazardly. I think it's important to understand that these are electronic devices that digitally alter the signal feeding the loudspeakers. They do nothing to sound waves. This is why I have a hard time calling them "room correction" products.

  • @Custom_Controls
    2013-11-20 08:46:34

    Really enjoyed this article guys! Great to see someone banging the drum to show a good installer is worth their weight in gold.

  • Morgan Henderson
    2013-11-20 02:01:51

    Thanks for this overview. I have a Denon 3808 which features the MultEQ XT. I find it does a good job with the things I can measure, like distance and channel level, except that it is useless at setting the sub cross-over point. I have found that, with Audyssey on, there is some negative impact on the audio, especially the higher frenquencies, but it is more than made up for by a profound improvement in imaging. With two-channel audio. the image becomes much more solid and centred, and, with the right mix, impressively three-dimensional. I have run the Audyssey calibration several times (swapping out gear, experimentation. etc.). Initially, I was using all eight calibration points, assuming I was getting a better reading of the room, but, as I don't have eight seating positions, began to wonder if that meant it would try to provide correction to areas that don't need it, as no one would be sitting there, potentially negatively impacting the correction on those areas where people would actually be sitting. It has been awhile since I did this, but my impression at the time was that the sound was better with only taking readings at seating positions. As your write-up on Audyssey seems to support my initial assumption, I'm wondering if you might comment on this. Thank You, Morgan

  • Devlon
    2013-11-20 01:57:08

    Great Overview Dennis! Good reading! I own the Sherwood Newcastle R-972 with Trinnov, and you are spot on about its freakiness, lol. In the 3D "Neural" setting the speakers disappear into the walls, sound then comes at you 360 degrees, yet you can pinpoint the position of the instruments/vocalist within the sound stage.....crazy! I totally agree with your opinion about EQing only the lower frequencies. I have the Sherwood/Trinnov to only EQ 300hz and below. On Dirac, it seems that Dirac in the XMC-1 will be like the Anthems in that room control will be via PC. Should be interesting.

  • stacey
    2013-11-20 00:52:40

    JL audios bass ARO was also missed from the list. I have the Marantz 7007 which uses the MULTIEQ XT. Does the ARO in the JL cancel out the AUDYSSEY or vice versa?

  • Jack Shafton
    2013-11-19 18:25:53

    Great summary Dennis. On the corrected frequency limitations subject, one thing I have heard many times is the idea that the "room correction" becomes "speaker correction" instead, when allowing the EQ to work above the switchover point. You can imagine what speaker designers think about that! Regarding ARC, one of the reasons ARC is so good is the use of an individually calibrated microphone, HUGE benefit for accurate corrections. (Also, unless something has changed, ARC does not do distances.)

  • David
    2013-11-19 17:51:21

    Hi Dennis. Please can you explain why you set your Anthem room correction to stop its EQ at 500 and 600hz instead of the maximum the program offers. If I sent you my graphs would you be able to offer some advice. Tks

  • Dennis Burger
    2013-11-19 16:43:08

    @palmharbor:disqus, one thing that may help you is getting your hands on an SPL (sound pressure level) meter. If you have a smart phone, there are a number of apps available that do the job of a dedicated SPL meter (my favorite is actually the sound meter included within the AudioTools app at, although it is available on its own for much less coin). Setting your speakers to the same level by ear can be tricky, but with an SPL meter you can ensure that all of your speakers are balanced from your main seat. Unless I'm running ARC, I always balance my levels manually after running auto-calibration.

  • jerrydel
    2013-11-19 16:34:49

    I wasn't sure if they were still around. They are an old client from the past - AVRev days.

  • Dennis Burger
    2013-11-19 16:31:13

    D'oh! I completely missed that fact. You're correct. When I laid hands on the XMC-1 last year at Emotiva's headquarters, TacT was part of the equation. I missed the fact that it had been replaced with Dirac Live. Thanks for the correction!

  • Arthur Miller
    2013-11-19 15:37:58

    No mention of DEQX

  • Random poster
    2013-11-19 15:20:43

    Dirac is also missing from the list.

  • petew
    2013-11-19 15:11:47

    quote "TacT room correction was also limited to the company's own preamps and room correction processors, but it will soon be available in Emotiva's new XMC-1 pre/pro." Emotiva dumped TacT in favor of Dirac Live™

  • Ken DeLoria
    2013-11-19 14:58:38

    Good article Dennis. Well researched. One thing about reverberant rooms though, as they get larger (and therefore more reverberant) the natural resonance of the air mass in the room increases and CAN be reduced to a flat response by EQ (analog or digital). It takes a high-resolution FFT to identify the resonant points and some skill to flatten them. This acoustical effect differs from standing waves which are additions and cancellations when the waveform meets itself in some degree of in-phase or out-of-phase. Also, in very large rooms, like dubbing stages, it's possible to install large and deep absorbers and/or bass traps, just as it is in recording studios. Expensive proposition, and not something the mainstream market is going to be able to do, but worth mentioning for the 'price is no object' meg-home theatre situation. All the Best! Ken DeLoria Senior Technical Editor Live Sound International Magazine / Pro Sound Web

  • Phil BRABANT
    2013-11-19 14:50:17

    I have this feature on my Marantz AVR 4310 CI. I have found multiple times that after it is done with its work: center channel has too low output….back surround way too loud and bass is much too low. I just put all the output except for base…the same…sounds just fine. On Audyssey site, I read many of the same complaints…their answer is mostly…get used to it.

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