Is room correction cheating?

Matthew J Poes · Oct 24, 2017

ok I know my starting premise is a straw man to begin with. It’s not a game to be won or lost. None the less I’ve at times felt a bit like the use of correction is somehow cheating. That the speakers and room should be right to begin with.

Not that I care if it is cheating, this is about enjoyment. If I enjoy music and movies more, then it is better.

Now the real point. I’ve been asked to attend AXPONA with an importer to address his acoustic needs. His gear is purist in nature. Tube amplifiers and high quality DACs and speakers. It feels to me like the right solution is to keep a purist approach and avoid additional things in the signal chain and focus on the rooms acoustics. Do it right and I’ve helped put this importer on the map. His room will be the talk of the town, so to speak. Do it wrong and any failures in sound quality are on me.

Here’s the rub, I know that if I just place a Dirac room correction device in the digital signal path, I could leave half those panels at home and likely achieve superior results. It could correct for significant room distortions that I would otherwise have trouble resolving.

Sonnie · Oct 24, 2017

I certainly wouldn't shy away from using electronics in the fix. Think about the recording engineer and what he/she does to the music/sound in a recording. There is all kinds of processing going on. All we are doing is trying to get the sound back to what was intended, by whatever means necessary.

Flak · Oct 24, 2017

MjPoes12 said:
Now the real point. I’ve been asked to attend AXPONA with an importer to address his acoustic needs. His gear is purist in nature. Tube amplifiers and high quality DACs and speakers. It feels to me like the right solution is to keep a purist approach and avoid additional things in the signal chain and focus on the rooms acoustics.

A purist approach disdains filters but (at least from my biased point of view) a purist should take into account that placing a speaker in a room means applying a filter...
the speaker position, the listening position and the room "decide" what this filter will look like.
Moving the speakers and listening position, even slightly, will change this filter that affects impulse and frequency responses.

Because of the above trying to attenuate the effects of the "room filter" with Dirac Live is a legitimate purist approach that can successfully cohesist with passive room treatment (if appropriate they will support each other)

In my opinion of course, Flavio

Matthew J Poes · Oct 24, 2017

Thanks Flavio and Sonnie. I completely agree with both of you. I suspect I will need to convince the importer of this as well, I doubt he will agree. I may try this with him to show him how much better it can be.

I noticed that a lot of people talked about how much better rooms sounded with digitial room correction at RMAF, it seemed like a hot topic this year even amongst the purist audiophile systems. These shows paces are terrible acoustic environments. I've been thinking about writing a post on room effects. Hotel rooms are built using common soundproofing approaches, and while not quite up to the standards of home theaters and studios, they are FAR superior to typical home construction methods. This means these rooms reflect far more sound than normal and that this will extend well into the bass range. They are also often unusual shapes, which only makes things worse. Highly reflective walls create real challenges.

Wayne A. Pflughaupt · Oct 24, 2017

It’s a common mistake to assume as such, but so-called room correction (a misnomer) and acoustical treatments don’t have a lot do with each other. As an extreme example, if your room is made of glass and reverberates and echoes like crazy, there’s nothing room correction or equalization can do for that.

Check out this little chart below I came across some years back on another Forum, that shows the effects of treatments in a room:

With the top row of boxes, the room has no treatment and has lots of reflections, as the ETC graph shows (column A). The audible effect of the reflections is seen in the ragged frequency response with lots of comb filtering (column B). Notice that as treatments are applied (e.g. the rows progressing top to bottom), frequency response becomes less ragged and more linear.

But notice the “B” box in the last row: Even with optimal treatments in place, frequency response is still less than optimal. So, even though the treatments tamed the reverberation, they did nothing for the anomalies in response. EQ is needed to address that.

Regards,
Wayne

Matthew J Poes · Oct 24, 2017

Hi Wayne I was largely referring to room correction below the schroeder frequency. It is both required as a function of minimum phase and well proven in practice that corrections arround and below the transition zone reduces both steady state amplitude and ringing. It absolutely is correcting the room.

Further, above this point in the stochastic region the mixed phase filters can correct for phase and amplitude distortions caused by the room. I stilkk consider this a valid description of room correction. It won't eliminate the reflection but undoes the distortion in the steady state.

I agree with you that you can't separate these and that traditional room correction is still needed. My point was that I can gain improvements in the response including DIRAC in the mix that I can't get with just traps and panels unless I use a lot of them, a lot more than I can reasonably use.

If you look at my theater pictures you will see that it is heavily treated in the traditional sense. I still use room correction to achieve greater improvement than otherwise possible.

Matthew J Poes · Oct 24, 2017

Here are a set of measurements I took before and after adding a bass trap and two additional panels to my already treated room which shows a similar improvement to that book.

Matthew J Poes · Oct 24, 2017

This is an older one from when I had only put up the linacoustic on the front wall. No bass traps, no cloud, no side wall treatments

Ignore the 500hz dip. It kept showing up and turned out to be caused by the position of the cord near the mic tip. I didnt realize until later when I moved the mic and chord and got an otherwise identical result without the dip.

AudiocRaver · Oct 25, 2017

"Cheating" infers being unfaithful to some standard. What is the standard we are referred to? And how faithful does one have to be to that standard to be considered "faithful" to it?

In the case of room correction, the only standard that really matters is Does it sound good? When applying room correction, Does it sound better than without room correction? Room correction can and usually does involve introducing a combination of positive and negative effects. In a room that is sorely in need of treatment, or perhaps even a fire and a clean start (a bit drastic and not generally recommended) room correction can definitely make it sound worse. These rooms are usually not hard to spot. A high RT60 can be a good first indicator of such a room.

In most cases, room correction helps, meaning that the negative effects are far outweighed by the positive. Part of the reason I like Dirac Live is that it applies a certain degree of processing intelligence that helps it determine what correction factors can be applied to give positive improvement without introducing negative effects.

There are certainly those who preach and teach that room correction is wrong and should never be used, and those who can cite and misquote studies to support that belief. I am aware of no study that proves categorically that room correction is always a bad thing, always doing more harm that good. Those who try to convince otherwise are usually motivated more by a personal agenda than by good sound.

Edit: Beg pardon to the OP, I was not implying that you were "misquoting studies," I was simply stating that there are plenty who tend to do that. Thank you for your thorough and thoughtful remarks.

Tonto · Oct 25, 2017

Here here, I think we all agree that setting up the room for best response by finding the correct speaker placement, then treating as much as we feel we need, then running a correction program produces the best result. Is this cheating...absolutely not! It's helping us enjoy the music to its fullest.

Matthew J Poes · Oct 25, 2017

Of course you are right in an objective sense. Right is what sounds right. Right is what measures right. Right is not an arbitrary set of purist rules.

I think my real point was this: if a person walks into a showroom or an expo and sees a system that is very simple, uses tube amps, high quality components, a minimum of extra fuss, will they be bothered by the correction being added? I think the answer is yes, they will see it as potentially corrupting the signal path. I’m not saying they are right, I’m saying I think that will be the thought process. They create a world view of purity that relies on a notion that everything added to a signal path corrupts and so must be kept to a minimum for maximum purity.

I think a separate notion that follows the same logic is that a truest skilled acoustician can make a room great through acoustic treatment alone. That better results can be achieved through acoustic treatment alone and in fact once that is achieved the room correction is not adding value, it’s doing more harm than good.

My world view is that is wrong, that whole room correction does not replace standard room treatments, it does enhance them in a way that can’t be readily replicated through treatment alone. The bass alone is an example of what room correction can fix that really can’t be equaled through bass trapping and panels. However I’ve found that no amount of room treatment will ever allow an otherwise smooth speaker response to be as smooth in room, but room correction using intelligent averaging techniques and mixed phase filters can take it to that next level. In other words, I see it as a critical tool no different than he panels. It’s a part of being good at acoustic treatment.

AudioThesis · Oct 31, 2017

To all,

I am the one who asked if Matt was interested in working with me at AXPONA. While I don't oppose digital EQ programs, I do oppose when they are 'added' to the chain. The reason for this is simple. Adding another electrical component to the chain will increase the noise floor of the system and while it may not show up tonally, it will cause things like soundstage shrinkage (no man likes that!), blurred imaging, and a host of other stereophonic qualities that can be compromised. I am hoping/expecting to have the North Star Design streamer back in the mix as I used a prototype for RMAF. In this scenario, Roon uses DSP and I am OK with that because no A/D conversion is happening. It is all handled in the digital realm and requires no additional hardware or steps in the chain to implement. When the A/D conversion happens, us 'purists' do believe more harm is being done than good and we will balk at it.

DSP has come a long ways over the past 6-8 years and is no longer a 4 letter word in the audiophile community. I still prefer for all passive elements to be considered first, but that isn't really an option in a setting like an audio show.

Just to clarify for you bud - all you need to worry about is helping me enhance the sound. If the room sounds bad, that is on me. If it sounds great, then we both gain benefits. My biggest concerns will be first reflection points and any dead or live zones the room may have. Obviously there is more to it, but that will be the fun of setup!

I've enjoyed reading this thread so far.

PS - I did actually implement some small DSP changes via Roon at RMAF. I am admittedly not as technical as Matt is and I'm hoping to learn some techniques in the process to improve that aspect.

Matthew J Poes · Oct 31, 2017

thanks Skip. You and I can chat privately about details of the options.

From a public standpoint, I think dsp eq has become too important to ignore as part of a room treatment scheme. However, it feels like cheating to me in the sense that I can get gains in smoothness that would have taken an insane amount of bass trapping.

Here is the 24”x24”x36” bass trap I built for the GTG.

To equal the impact of an eq device, I would need to deploy roughly 10 of these strategically, if not more.

As for being responsible, Skip I treat my work as a reflection of me. If my work doesn’t meet my expectations I will feel responsible. It’s just my work ethic. If this room isn’t one of the best sounding rooms I’ll feel like I let you down. Hence why I want to do this right.

I was totally shocked to read about the deployment of digital room correction in so many rooms at RMAF and the positive feedback it got. It wasn’t long ago that was treated as a strange curiosity or junk best left out of an audiophile system.

AudioThesis · Oct 31, 2017

Not long ago in order to use DSP an additional step was required. It was necessary for the signal to be converted from digital to analog and then back to digital to send out to the DAC. There was great harm done in this process. Since new DSP can be applied in the digital realm, more have come on board with the idea and you are beginning to hear success stories.

I think the most important area of DSP is 200hz and below. Most higher frequencies can easily be tamed by treatments. The lower frequencies are usually the culprit in destroying tonal balance as well as the stereophonic qualities if they are abundant.

In a way I fear DSP because if used liberally you can completely lose what a system is capable of and end up listening to the EQ instead. It is a double-edged sword. A good example for me is the KEF LS50. The passive speaker is ringy and unpleasant to many I know. The active version with DSP gets much better reviews from these same people. Are we listening to the speaker or the processing? In the end it might not matter, but it is a good topic of discussion.

Matthew J Poes · Oct 31, 2017

AudioThesis said:
Not long ago in order to use DSP an additional step was required. It was necessary for the signal to be converted from digital to analog and then back to digital to send out to the DAC. There was great harm done in this process. Since new DSP can be applied in the digital realm, more have come on board with the idea and you are beginning to hear success stories.

I think the most important area of DSP is 200hz and below. Most higher frequencies can easily be tamed by treatments. The lower frequencies are usually the culprit in destroying tonal balance as well as the stereophonic qualities if they are abundant.

In a way I fear DSP because if used liberally you can completely lose what a system is capable of and end up listening to the EQ instead. It is a double-edged sword. A good example for me is the KEF LS50. The passive speaker is ringy and unpleasant to many I know. The active version with DSP gets much better reviews from these same people. Are we listening to the speaker or the processing? In the end it might not matter, but it is a good topic of discussion.

Today’s room correction systems come in two flavors and I like each in different ways (I know dsp experts don’t characterize it this way, but for the average person this is easier). You have minimum phase filters (e.g. PEQ) and FIR (e.g. mixed phase filters, linear phase, etc. ). In the low frequencies many think PEQ is best, when deployed right, and I tend to agree. Above the transition zone of a room you can’t use PEQ without doing more harm than good (a little of a correction might be ok, but you have to be so careful). That’s where systems like DIRAC come in. They are so controversial among experts, but I’ve heard them deployed across many systems and I’m a total believer. These dsp systems are now a part of the speaker as much as anything. You just can’t separate them anymore. It doesn’t shock me that the active KEF sounds better. It should, they have all these tools at their disposal.

With a system like DIRAC there is no risk of this, but with a amature implementation of FIR correction you can do serious harm to the statem. These filters tend to have a lot of pre-ringing that needs to be balanced against the gains.

Allen Rumbaugh · Nov 1, 2017

Can you take the REW measurements of the speaker at one meter in a circus tent or outdoors, do a phase correction on the speaker itself, then install the speaker in an acoustically treated room, run one DIRAC for loudspeaker correction, then use another DIRAC for room correction? it seems to me that would really take advantage of the DSP to kill two birds, what do you think?

tesseract · Nov 1, 2017

Digital room correction is so far removed from the analog EQ's that of yore that caused phase issues. The most successful audio show exhibitors have begun to realize the edge that DSP gives and anyone not jumping on board today will be doing so tomorrow.

AudioThesis · Nov 1, 2017

I'm not interested in changing the speaker's or system's inherent sound. I know many go for a linear response but that isn't my prerogative. I want an engaging and emotional experience, not a 'correct' one. What I do want to change is the impact the actual room has on the sound. This allows the gear to shine as intended.

For a long time, the high end and ultra high end chased this ruler flat linear sound. Pair that with extracting every single detail you can out of a recording and you end up with a very unconvincing sound. You are beginning to see a shift in this as more and more companies are beginning to get a little 'soul' added back to their sound. Maybe we are getting to the point where you can have both? I don't know, but I do know that the 2 channel world is headed in the right direction with the experience coming first and not the technical correctness of years passed.

Matthew J Poes · Nov 1, 2017

AudioThesis said:
I'm not interested in changing the speaker's or system's inherent sound. I know many go for a linear response but that isn't my prerogative. I want an engaging and emotional experience, not a 'correct' one. What I do want to change is the impact the actual room has on the sound. This allows the gear to shine as intended.

For a long time, the high end and ultra high end chased this ruler flat linear sound. Pair that with extracting every single detail you can out of a recording and you end up with a very unconvincing sound. You are beginning to see a shift in this as more and more companies are beginning to get a little 'soul' added back to their sound. Maybe we are getting to the point where you can have both? I don't know, but I do know that the 2 channel world is headed in the right direction with the experience coming first and not the technical correctness of years passed.

Actually there is another very real reason to not use something like DIRAC. Your speakers have ribbon super tweeters and Dirac requires specialized hardware to run above 48khz sampling. The readily available hardware that allows you to avoid redundant ad/da conversion and a computer in the signal path is stuck at 48khz due to hardware limitations. It would defeat the whole purpose of that supertweeter.

Matthew J Poes · Nov 2, 2017

tesseract said:
Digital room correction is so far removed from the analog EQ's that of yore that caused phase issues. The most successful audio show exhibitors have begun to realize the edge that DSP gives and anyone not jumping on board today will be doing so tomorrow.

That’s certainly true of Dirac and Audyssey, that isn't true of YPAO, MCACC, ARC, EmoQ, etc. These all use various forms or IIR filters. The Yamaha and MCACC systems offer phase correction but it's always been unclear to me how it works, what it does, and I've never measured anything to help me understand.

My point about this earlier was you can apply IIr filters in the stochastic reason but only if you measure free space. Of course you can use Dirac in room and it's all a non-issue.

Matthew J Poes · Nov 2, 2017

Allen Rumbaugh said:
Can you take the REW measurements of the speaker at one meter in a circus tent or outdoors, do a phase correction on the speaker itself, then install the speaker in an acoustically treated room, run one DIRAC for loudspeaker correction, then use another DIRAC for room correction? it seems to me that would really take advantage of the DSP to kill two birds, what do you think?

DIRAC actually uses its own measurement system and not REW. The love of DIRAC around here is more a coincidence than anything to do with REW.

there are in fact correction suites focused on linearizing the speaker bases on it's free space measurements and then correcting the room seperately. I actually like the concept or this approach but it's not end user friendly.

The problem starts with your circus tent idea. It's actually very difficult to measure a speaker in free space accurately without specialized equipment that would be unreasonable. You need to lift the speaker off the ground a good 15-20 feet or more. It would need to be a good 100 feet or more from any other boundary. It would also need an ambient volume below 35db or so to be useful. You would need full polar measurements on the speaker too, as you would want to linearise the phase without correcting odd anomolies.

There are a few correction systems that could do this, dirac isn't one of them. The effort is so great I've not bothered to try it myself. You could theoretically focus on just linear phase in the crossover and that could be done with a single near field measurement I think.

Sonnie · Nov 2, 2017

I get a much more emotional experience with DL (Dirac Live) engaged on any speaker I listen to in my room. I could care less about correctness, although I enjoy looking at the response. The sound stage is better, imaging is tight and precise, and depth acuity is improved, which all contribute to a more exciting sound for me. The sound without DL (in most cases) is boxy, muffled, and it just doesn't sound very good in comparison. I can't imagine any recording engineer intending anyone to hear music this way, nor would it sound anything close to this bad (my opinion only) in the studio.

We have experimented with countless speakers and their placement in my room in an attempt to improve the sound without DL, but just can't get there, at least not for me and most that have been there and listened to both. I've not had anyone say that they prefer the sound without DL on most music heard in my room, over the sound heard with DL. There might be a particular poorly recorded song that may not benefit from DL on a few speakers, or some songs that have particular characteristics that are more fun without DL (exaggerated bass, etc), but in almost every case, something else suffers because of it. Granted, other rooms may speak differently to other ears, I just haven't heard them yet. And... people have different listening preferences. I'd would greatly suggest listening both ways and choose what you like the best. I happen to be one of those that haven't been able to live without DL on anything I've heard. The sound it that much better to me.

AudioThesis · Nov 2, 2017

It happens Sonnie. I went to a friend's house and he uses the KEF LS50W with DSP engaged. In his situation, it is the best fit for his room because his room is atrocious. DSP definitely has its merits and implementations.

In most instances, simply cleaning up the bass frequencies does wonders for your stereophonic qualities. First reflections are a must to treat, but first reflections do nothing for those lower frequencies.

Sonnie · Nov 2, 2017

Yep... the bass is where you see the most issues if you are looking at the graphs, but treating those with panels is no easy task, especially that 30-60Hz range. I would think if you could clean up the bass that would be my biggest concern, and it is what I seem to notice more so in the sound than the upper end. The bass issues stand out a lot more, or so it seems. It's what gets my attention the most.

AudioThesis · Nov 2, 2017

I've found that bass is often the most fatiguing when out of whack. It's usually that type of fatigue where you don't know why you are tired of listening, but you are and your head hurts after the session. Unlike the highs that grab your attention right away, the bass wears on you over time.

Is room correction cheating?

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