Reprinted with permission from

w w w. h o m e t h e a t e r h i f i . c o m

Reviewed by Brian Florian

reviewP R O D U C T

ARC, or Anthem Room Correction, hasbeen a long time in coming. Its origins canbe traced back as far as 1990 to researchconducted at Canada’s NRC (NationalResearch Council). Under the supervisionof Floyd Toole, the NRC had previouslyperformed landmark research into loud-speaker performance. Statistical analysisof controlled listening tests showed that there was a common thread amongspeakers which subjectively “sound good”:in an anechoic chamber they were theones which measured a neutral response,free of coloration. This research literallylaunched companies like Paradigm who,rather than vaguely poking at speakerdesign, now had a solid definition of whatexactly made a good speaker “good”.

On the heels of that research came theAthena project in 1990. Whereas theprevious research looked at many different

speakers, Athena looked at only a handfulof speakers in many, many different rooms.Here again, a common thread was foundbetween what statistics showed to be goodsounding rooms. I’ll jump ahead just a bitand tell you that it is not what you’d think.

Armed with this data, the next step wouldbe to create a system which could shapethe speakers’ response to get the systemsounding more like the preferred rooms. Itwas only a matter of time, over ten yearsactually, until DSP power in audio processorswas up to the challenge, and a filteringsystem capable of the incredibly complextask could be put into play.

WHAT’S IN A NAME?The term Room Correction, ubiquitouslyused in this context, is unfortunately not theindustry’s best choice. Room Compensation

would be far more accurate. A small distinct-ion of semantics, but a necessary one.

Going back about a decade, several earlyautomated EQ/filter systems were billed as“speaker correction”, which is not a badway of describing it, since you are in factchanging the signal to the speaker and con-sequently what comes out of it. The troublewith that name was that it made the featurequite unpopular among audiophiles: no onelikes to think there is something “wrong”with their speakers, which needs to be corrected.

Since that time, there has been a growingcognizance among consumers, especiallythe more serious enthusiasts, with regardsto acoustics. It is now undisputed that “theroom” has far more influence on systemperformance than any piece of the system’selectronics. It is my own adage that if forced

EXPERIENCED IN TERMS OF ALTERING,

“ARC IS LIKE NOTHING ELSE I HAVE

FOR THE BETTER, A SYSTEM’S SOUND”

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to make a hypothetical choice, I would always rather have a modest hardware setupin a room with good acoustics than havestate-of-the-art hardware in a poor room.But addressing acoustics ranges from theinconvenient, to the expensive, to the down-right impossible. It is small wonder, then,that these new automated filter/EQ systemshave now consistently, though in my opiniondeceivingly, been billed as “room correction”by just about everyone. Unfortunately,marketing departments have pushed forththe notion that by simple application of afilter, the room somehow magically disap-pears and you are transported to the likesof Dolby or Lucasfilm’s own state of theart mixing facilities.

Simply stated: that is not happening. With-out thinking too much about the issues involved, it would seem plausible that ifyou take a measurement of the system’sfrequency response in the room, and thenapply a filter as an inverse of that response,everything would null out and audio nirvanawould result.

There are two problems with this sentiment.The first is that it only works that way forone person and one person only, with theirhead in a vice at that, since the effects ofthe room change according to your positionin it. The second is that the room does notdisappear. You might change the soundcoming from the speakers, but that soundis still bouncing around. You can’t stop latearrivals and decaying reverb with electronics.Acoustical treatment is the only way to actually alter acoustics.

Room Correction is not a substitute for addressing acoustics (nor is any other auto-mated EQ/Filter systems, regardless of howthey are marketed). However, as you will seein the coming paragraphs, ARC ultimatelyis an equally important part of the systemperformance equation, on par with roomacoustics. It is a unique must-have com-ponent, whether your room is acousticallypoor or excellent.

ARCARC is the most recent addition to Anthem’sfamed D2 Audio/Video Processor Preampor Surround Sound Processor, i.e., SSP(existing D1 or D2 owners can purchase ARC-1 as an add-on kit).

The system consists of three elements: A calibrated USB microphone (completewith robust mic stand), the ARC computer software application, and supporting firmware for the D2 itself. Unlike most such

systems on the market, ARC requires a PCto set it all up due to the complexity of thesystem. Just how sophisticated it is will beapparent in a minute.

The software comes with a license filewhich will only work with a single D2 andmicrophone serial number combination.Installation of the Windows application isstraightforward (and works just fine underWindows Vista by the way). The suppliedmicrophone connects to the PC via its longUSB cable, while the PC connects to the D2via an RS-232 serial cable (if your PC doesnot have a serial port, you will need yourown USB-to-RS-232 converter). On launch,the software presents you with a choice ofStandard or Advanced operation.

The Standard option is like a setup wizard.You start by telling the system whichchannels you have (i.e., what your speakerconfiguration is). You can have completelydifferent setups for Movies and Music. I amdiametrically opposed to the notion that thetwo source materials need different settings.The performance metrics of Hi-Fi audioreproduction do not change with media.Hi-Fi is Hi-Fi, period. The feature does havea couple of very good inadvertent uses: youcan define a much narrower listening areafor one mode compared to the other such thatyou can have one mode optimized for atheater full of people and the other optimizedfor when you are the sole critical listener. Inaddition, having two different setups makescomparing different ARC settings a breeze.By setting different “targets” (which we’llexplain in a moment) for Movie and Music,one can very easily A/B the different settingslater by flipping between the Movie/Musicpresets in the D2.

You must also tell the system how many seatsyou have (or really how many locations inthe room to measure). ARC requires you giveit a minimum of five positions to measure.Even if you have just, say, two chairs, youmust take measurements at least five positions, and they must be at least 12 inchesfrom each other (preferably 20). Althoughat first it may seem pointless to measurewhat the sound is like in places no listenerwill be, this minimum is imposed so thatthe system doesn’t misinterpret what it ishearing in the actual seats in terms ofidentifying what is a room mode and whatisn’t (in other words, one or two measure-ment positions just don’t tell you the wholestory of the room).

If you chose the Standard option, that’s theend of your input. The system will ask youto get the mic ready in the first central, orprime, seat, the PC will then take control ofthe D2, ordering it to cycle power, and startthe first set of test noise bursts through eachspeaker. You’ll be prompted to move the micto the second position, it will repeat the testnoise bursts, prompt you to move the micto the third seat, and so on. The softwarethen crunches the numbers, figures outbasic setup parameters such as speakerlevel and distance, sets crossover points,and ultimately figures out what filter it isgoing to apply to each speaker. Its last stepis to send all this data to the D2, and youare done. You can go into source setup andmake sure it indicates that EQ is on.

The Advanced mode is much more interesting.

You start the same way, but on completionof the measurements, the application showsyou a frequency response graph for eachspeaker. These graphs are a simplificationin that they represent an average of all themeasurements taken for each speaker, yetthe system is using the separate measure-ments from all positions to calculate therequisite target curves and filters.

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It’s all about hitting the target. When werefer to the target, we are talking about whatwe want the sound to be, never mind fora minute how we actually do it. Counter-intuitively, ARC does not attempt a perfectlyflat speaker response for several very goodreasons. The first is that it is impossible toget a perfectly flat, or even uniform, responsefor every listener in a room, so there is nopoint in trying. The best systems, like ARC,aim for a “best overall” fit. That’s not new,as other systems do the same. What isunique is the fact that Paradigm and Anthem,through their many years of user-listeningexperience and leveraging the Athena projectwe mentioned earlier, really know whatconstitutes “good sound”.

Some stuff matters, some stuff doesn’t interms of psychoacoustics. What ARC bringsto the table is unique: its particular set ofaudio and room characteristics which theirresearch has shown to be the most signifi-cant and “worth” fixing, as well as that whatis not and is best left undone. One of themore tangible aspects of this is the conceptof room gain, and is one of the target settingsyou have control over. Room gain is basicallythe amplitude boost any audio source (be ita speaker or even your own voice) gets in theupper mid-bass range from the boundariesof the room. Filter, or correct for this naturalboost, and you end up with an unpleasant,dull sound because our ear-brain just “expects” room gain. ARC assumes you arenot using poor speakers and thus when itsees a common “swell” in the frequencyresponse of the measurements, considersthat to be room-gain and, here is the key,does not target it for correction the way itdoes a room mode. In other words, if youlook at the target curve in the graphs, it hasa very shallow hump (in my case about 4 dB)in the upper bass, and yes, we want that.

“Flipping ARC On/Off is ahumbling experience. ARC‘On’: clear, articulate sound.ARC ‘Off’: someone draped ablanket over the speakers.”

But isn’t that distortion? Yes and no. First,it is by any stretch very mild in amplitudeas compared to other aberrations in thesystem’s response, yet correcting it is in avery real way worse than keeping it. I waschallenged by Anthem to “just try it” byaccepting all the recommended target settings for Movie mode, and zeroing out

the room-gain for Music mode. Indeed,correcting room gain makes it sound very dead, literally.

Another parameter you can play with in thetarget settings is maximum frequency tobother filtering or correcting at all. Anthemelects 5 kHz as a default here. It’s not thattheir filters can’t keep up, but it gets socomplicated and messy up there that thereis virtually nothing you can do electronically(unless you have really bad speakers,which ARC assumes you don’t).

“… made a profound differencein my setup — in ways I didnot expect or even dreamedneeded help … low end ismuch tighter and more precisetonally … It is the midrange,the vocal range in particular,which floored me … the onlyway I can, in typed word, describe to you the differenceis to say it is the differencebetween muffled and clear sound.”

Here is a prime example of how and whyacoustical treatments will always be equallyimportant alongside ARC: nothing controlsand focuses treble like some absorptivepanels strategically placed at first reflection points.

Also, part of the target settings is the cross-over frequency for each speaker. This is onethat is really going to ruffle some feathersas, with little exception, ARC will tend touse higher frequencies than people wouldexpect, sometimes much higher. It’s notuncommon for ARC to select upwards of160 Hz for what some people consider full-range speakers. It’s also not uncommon forit to pair that with a subwoofer low-passof 80-100 Hz. In other words, ARC will inmany cases intentionally create a “hole” inthe system’s electrical response, becausethrough a combination of the filtering andthe room itself, the difference ultimately istaken into consideration (plus you get anice headroom bonus as compared tocrossing everything over at, say, 80 Hz).

People with big tower speakers are notgoing to like learning that the best fit forthem in the room with ARC’s help meanshigh-passing them at something close to100 Hz, but they are going to have to getover it. What comes first: your pride, orgetting the best sound possible?

You can, of course, override these cross-over frequency choices at this point, andalthough Anthem is confident with whatthe system chooses, depending on yourparticular speakers and moreover the position of your subwoofer, you may wantto force a lower crossover. In my case, forexample, ARC elected upwards of 160 Hzcrossover for my front channels, whichyielded excellent results but ended upleaving me with a subwoofer which simplydrew too much attention to itself. Forcingeverything to THX-80 Hz still “worked”,though I may have sacrificed a little of whatARC is capable of by doing so. Regardlessof why you want to change the crossoversettings, if in fact if you do, you must doit here within the ARC PC software, as thecalculation of the final filters are done hereand takes the crossover frequencies intoaccount. If you change the crossover fre-quencies in the D2 after the fact, ARC willbe thrown completely out of whack.

Once you are satisfied with the target settings,the next step is for ARC to calculate the actualfilters it will apply. This is heady stuff.

ARC uses minimum phase IIR (InfiniteImpulse Response) filters instead of themore common FIR filters, since these last,especially at low frequencies, incur longdelays which are complex to account for.

For those who love numbers: from the microphone’s 16-bit integer data, signalprocessing calculations on the PC are donewith 64-bit floating point values, yielding24-bit fixed point coefficients downloadedto the D2. The IIR filters in D2 have 56-bitfixed point accumulation and use 1st ordererror feedback when converting to 24-bitfixed point.

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The net result of all the number crunchingis a green “calculated” curve which getsadded to the graphs. These are what theresponse would be if a hypothetical “post”measurement were taken. This curve is veryrevealing in that it does NOT look like aruler-flat response.

“Anechoic chambers sound like crap”. I don’tknow who first said it, but we all repeat itnow because they are words to live by.Seeking a ruler flat response with no “sound”from the room is not what we want. Graphsof Impulse Response measurements arereally misleading in this respect in thatthey make things look a LOT worse thanthey really are. Again, this goes back toknowing what matters and what doesn’t.

Take a look at the ones I’m showing you here.You would think my room and/or speakersare garbage, but I assure you neither is thecase. That’s not to say there aren’t somemajor issues to correct, sometimes more,sometimes less depending on the room, butit’s not as though rooms are as bad as anImpulse Response measurement graph looks,or more to the point that we would want itto look ruler flat.

The point is, what you do see in the visualsis an overall correction of the most egregiousdistortions. But no visual aid or graph isgoing to convey to you what ARC does toyour system … trust me, you have to hearit to believe it. I’ll explain in a minute.

USAGEBefore we talk about the “how it sounds”,a few notes on the package.

One way in which I was really disappointedis the mic stand. Anthem saw fit to includea real quality piece: solid telescoping shaftand a cast iron base with their logo. There’sjust one problem: It’s too tall! When set toits shortest stature, and placed in one of yourseats, the mic will be at least six incheshigher than where most people’s head wouldbe. I ended up having to extend it as far asit would go, set it on the floor in front of

the seat, and tilt it back until the mic endedup where it should be. And yes, that makesa difference. I did a set of measurementswith the mic at the “wrong” height, andanother with it at the “correct” height,and the graphs were notably different.

While anyone who owns a D2 almost certainly has a PC (or two or three), unlessone of them happens to be a Media Centersitting next to the D2, playing with ARC is areal hassle, at least for me it was (luggingthe PC down to the theater multiple times).Just something to be aware of.

Anthem has on their hands the makings ofa very sweet piece of software in ARC, andI hope they don’t leave it as is. Even thoughit’s not billed as such, you have a verypowerful, accurate sound measuring tool onyour hands. In the future, it would be nicefor example if we could take measurementsof individual speakers (as opposed to goingthrough the whole ARC setup process), sothat small changes in a speaker’s placementcould be hashed out.

IN PRACTICEI’ve listened to some other room correctionsystems, and at best, the improvements havebeen subtle. ARC, on the other hand, I amprepared to admit, made a profound differ-ence in my setup, and in ways I did notexpect or even dreamed needed help. Simplystated, with the exception of doing actualacoustical treatments, engaging ARC is likenothing else I have experienced in terms ofaltering, for the better, a system’s sound.

To put this last statement into perspective, Iam of the opinion that changes in audio hard-ware manifest differences in sound whichare best described as ranging from subtlyperceivable (such as different speakers) tobeing so slight as to question whether thereeven is a difference at all (cables anyone?).So when I say something makes a profounddifference, I’m not mincing words.

The bass now met expectations in that by principally correcting the nasty 52 Hzroom mode I knew I had, the low end isnow much tighter and more precise tonally.That’s not so amazing, as I’ve been able todo pretty close to that myself with a fewbands of parametric EQ. It is the midrange,the vocal range in particular, whichfloored me.

I have what I know for a fact to be excellent,responsible speakers both in the frequencyand transient response domains. My room,while not perfect, has at least a modicum

of acoustical treatments, leaving me with(relatively) decent overall sound.

Flipping ARC On/Off is a humbling exper-ience. I don’t quite know how to describethe improvements to the system’s soundwithout myself coming off as disingenuous.I’m the first one to point a finger at marketingdepartments for making incredulous claims.Yet here the only way I can in typed worddescribe to you the difference is to say it isthe difference between muffled and clearsound. Seriously. No joke. I’m not embellish-ing. If you don’t believe me, find someonewith a D2 equipped with ARC and listenfor yourself. Let me say that again. ARC“On”: clear, articulate sound. ARC “Off”:someone draped a blanket over the speakers.How can this be? I didn’t think my systemsounded that bad before the D2 with ARCarrived for review, and now I know that itdid by comparison.

The explanation is actually simple: ARC(and other such systems) are unique inthat by definition they let us do very properA/B’ing, something which brings into verysharp focus the actual manifestation of achange. Our auditory/acoustic memoriesare short, very short, and anyone who claimsthey have “expert” ears and are more skilledthan others at this stuff may be delusional.

“What ARC brings to the tableis unique … trust me, you haveto hear it to believe it …”

That goes back to Floyd Toole/NRC research.It appears that 99% of audiophiles will neverbe able to A/B anything properly for simplelack of the requisite tools. The time it takesto, say, replace a speaker is usually too long.In order to properly A/B two loudspeakersthey must be run through a very specialswitch which compensates for differentefficiencies and impedance in order for aflip to be both fast enough as well as “fair”(I’ve had one such an opportunity, and Iwill say that ARC is at least as significantas changing speakers, and in fact I thinkmore so). A/B’ing ARC on the other handrequires nothing more than the D2 remote inyour hand, so the experience is somewhatstacked in its favor. The bottom line thoughis that if you want the best sound, you’llwant something like ARC, period.

By definition, what exactly ARC does isgoing to be different for every single systemit is implemented in, yet my reactions andobservations I’m told have a curious common

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thread with virtually all feedback that Anthemhas received to date, in particular with regardsto the tonality of the bass and the surpriseclarity in the vocal range. In other words, allrooms share some commonality which ARCis addressing, even though the acoustical signatures may be radically different. Itseems that all that research at NRC reallyhas born fruit because Anthem is not justcompensating for the room. ARC is actuallydoing one better than that by hitting theirunique “good sound” target.

CONCLUSIONSARC is a very scary product. If you are oneof those who insists on having the bestsound, and you experience ARC, especiallyif you can do so with your existing system,one of two things will happen: Either youwill buy a D2 with ARC, or you will stoplistening to your existing system knowingjust how much better it would be with ARC.

Think I’m waxing poetic? Think again. I dare you!

“… a unique must-have component, whether yourroom is acoustically poor or excellent.”