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An Enticing Marketing Story, Theory Without Measurement?

svart-hvitt

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#1
Is digital digital room correction just another story of theory without measurement? Generally speaking, there are two kinds of information: There are observations and there are theories. So generally speaking you can believe the observations and you don’t need to believe the theories. But where are the observations – competently managed blind tests – that support the theory of digital room correction?

This opening post is a bit long. My main point is summarized above, but I want to add some background and colour to the theme below.

In «The Measurement and Calibration of Sound Reproducing Systems» (http://www.aes.org/e-lib/browse.cfm?elib=17839), @Floyd Toole takes a position in the debate on «room correction» products. Toole wrote:

«For decades it has been widely accepted that a steady-state amplitude response measured with an omnidirectional microphone at the listening location in a room is an important indicator of how an audio system will sound. Such measurements have come to be known as generic “room curves,” or more specific “house curves.” That belief has a long history in professional audio, and now it has penetrated consumer audio with stand-alone products and receivers in- corporating automated measurement and equalization capa- bilities. The implication is that by making in-situ measurements and manipulating the input signal so that the room curve matches a predetermined target shape, imperfections in (unspecified) loudspeakers and (unspecified) rooms are measured and repaired. It is an enticing marketing story».

He also wrote that «room equalization is a misnomer»:

«It is a bold assertion that a single steady-state measurement in a room—a room curve—can reliably anticipate human response to a complex sound field. Such measurements take no account of the direction or timing of reflec- tions within the sound field. Time-windowing the measurement is useful to separate events in the time domain, but these too ignore the directions from which sounds arrive. Human listeners respond to these cues, in some detail, and they exhibit skills in separating room sound from the timbral identity of loudspeakers, and in adapting to different circumstances. This is, after all, what happens at live, un-amplified, musical events. This means that not everything measured is perceptually important, nor can our reaction to such sound fields be constant, we adapt (see [1] chapters 5–11, and section 11.3.1, and [2] section 2.5). The simple measurements therefore cannot be definitive».

Room correction: An enticing marketing story and a misnomer. Strong words, right? And they origin from most merited member of AES. What is the audio interested person to believe? Are room correction products just another snake oil story?

@Floyd Toole isn’t all negative towards some equalization. He wrote:

«In conclusion, there are reasons to exercise great caution in the application of equalization based on conventional in-room measurements. However, it is definitely advantageous at lower frequencies, and later discussions will show that equalization based on anechoic data is also useful in the creation of superior loudspeakers».

I recently brought the Toole paper into a discussion on another forum with the author of a well known room correction software. He finds nothing of interest in Toole’s book and paper. And he found some of the claims in the paper unscientific, not least the notion on «enticing marketing story».

Given the impression that the «room correction» experts and Toole seem to live on different planets in the audio universe, I tried to understand the reasoning of the digital room correction author. He quoted Angelo Farina (http://www.angelofarina.it) and John Mourjopoulos (http://www.wcl.ece.upatras.gr/audiogroup/people/john.php) as two of his inspirations. This Farina paper was mentioned explicitly:

http://www.aes.org/e-lib/browse.cfm?elib=12683

I have looked at some of the papers of the two audio professors, as well as other papers on «room correction», for example by Dirac’s Lars-Johan Brännmark. Needless to say, I am no audio expert. And reading the papers makes it evident that the holes in my body of knowledge are big and many. So I cannot argue about consistencies and inconsitencies, of which many are of mathematical nature, in the papers. But there’s still a big déjà vu when reading these papers. I have seen this before, many times.

I remember these quotes from Freeman Dyson, quotes that come from another discussion but nonetheless cast light over many a debate on scientific rigour and my déjà vu experience:

«It’s a very dangerous game. If you work with a computer model for years and years and years, always improving the model, in the end you end up believing it. So it’s difficult to remain objective (…) Observations always should tell you in the end who is right and who is wrong. Those people don’t look at the observations. They are in a world of their own (…) Generally speaking there are two kinds of information: Observations and there are theories. So generally speaking you can believe the observations and you don’t need to believe the theories».

Toole is, as far as I know, the only person to have been honored with two gold medal awards by the AES. And if I am not mistaken I believe that Toole’s ability to support theories on sound reproduction by observations – i.e. competently managed blind tests – have contributed to his standing in audio science. What describes digital room correction, which Toole calls a misnomer, is the absence of blind tests. In 2009, Olive wrote:

«The sonic benefits of these room correction products are generally not well known since, to my knowledge, no one has yet published the results of a well-controlled, double-blind listening test on room correction products» (source: http://seanolive.blogspot.com/2009/11/subjective-and-objective-evaluation-of.html).

To my knowledge, there hasn’t been any «well-controlled, double blind listening test on room correction products» after 2009. Is the lack of observations – blind tests – the gorilla in the digital room correction room (sic!)?

The proponents of digital room corrections will argue that their measurements in-room are what Dyson calls «observations». But is sound, as it’s captured by a microphone, an observation in the true meaning of the word? Is a microphone a relevant substitute for human perception? This point is of great importance because it’s much cheaper to employ microphones than trained listeners. And if everything in audio can be modelled mathematically and proven by microphone measurements, why do we need cost-driving, unscalable listening tests, expensive anechoic chambers and great efforts in designing speaker drivers and boxes in the first place, if it all can be replaced by cheap drivers and boxes, a computer model and digital room correction? Corporate cost cutters should take notice if the modelers are correct, right?

I wish to underline that I have no stakes in this debate apart from a wish to generate some debate on and hopefully deeper insight into digital room correction, especially above Schroeder/transition frequency and the implicit search for the golden room curve, the one curve that rules them all, so to speak. For full disclosure, I employ digital room correction myself (the positive effects in lower frequencies are evident!), but wish to learn more about this theme and its scientific standing.

I think it’s fascinating that the digital room correction proponents have been working on their «computer model for years and years and years, always improving the model». Could that explain why they «in the end (…) end up believing it», in absense of observations? Does that explain why a discussion with one author of such a digital room correction program became heated, because «it’s difficult to remain objective»? How can it be that after over 20 years of digital room correction modeling, there is just one competently managed blind test in this important area, i.e. the one carried out by Sean E. Olive, John Jackson, Allan Devantier, David Hunt and Sean Hess in 2009 (http://www.aes.org/e-lib/browse.cfm?elib=15154).

Can we conclude that room correction is «a misnomer» and just an «enticing marketing story»? Why don’t we have more observations on this fascinating area?
 
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amirm

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#2
«The sonic benefits of these room correction products are generally not well known since, to my knowledge, no one has yet published the results of a well-controlled, double-blind listening test on room correction products» (source: http://seanolive.blogspot.com/2009/11/subjective-and-objective-evaluation-of.html).
??? Dr. Olive conducted exactly such a study and is linked there. Is there something wrong with that study?

There is also another indirect study that was published in another context which I have to try to find.
 

amirm

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#3
Can we conclude that room correction is «a misnomer» and just an «enticing marketing story»? Why don’t we have more observations on this fascinating area?
The room can't be corrected. It is always there. :) This is why I call it Room EQ. It is an EQ that is designed to counteract some of the effects of the room, but not all. You can't for example get rid of a right side room reflection. It is going to be there and no EQ can change it since the effect will be on both direct and indirect sound.
 

SIY

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#4
But is sound, as it’s captured by a microphone, an observation in the true meaning of the word? Is a microphone a relevant substitute for human perception?
Yes, to the former. No, to the latter. It's also not a substitute for human emotion or human creativity. It is a device which measures pressure versus time in a specific place, i.e., provides observational data of the sound impinging on a spatial point. I'll let eristics quibble over whether that's the same thing as "an observation."
 

svart-hvitt

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#6
The room can't be corrected. It is always there. :) This is why I call it Room EQ. It is an EQ that is designed to counteract some of the effects of the room, but not all. You can't for example get rid of a right side room reflection. It is going to be there and no EQ can change it since the effect will be on both direct and indirect sound.
Toole: «2.4 “Room Equalization” Is a Misnomer».
 

Cosmik

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#7
It is a triumph of measurement over logic. It is based on a vague, unstated assumption: that humans are purely frequency content analysers and that they can't distinguish between direct sound, reflections and reverberation; so as long as the contents of an FFT window more-or-less give the right proportions of 'frequency response stuff', it will sound perfect.

Logic and common experience tells us that this cannot be true, otherwise we would not be able to hear the directions of sound sources in reverberant environments, and people's voices would sound different as we walked from outside to inside. We have evolved, then learned all our lives, to distinguish between a sound source and reflections (a.k.a. 'the room'); we do it expertly and without conscious thought. In our hearing we are not eliminating the room, but we are distinguishing between the source and the room. If we change the sound source to fit some notional 'target curve' it will sound 'changed' but the room will sound just the same! - the opposite of what is intended.

Confusion arises because real speakers are often not very neutral sources, with odd directivity at different frequencies. This cannot be corrected, but it can be compensated for to make the speaker sound subjectively better. The room cannot be corrected, but the speaker in that room in that particular placement may be improved subjectively if there is some understanding of what is going on. Calling it 'room correction' is an indication that that understanding is absent...
 

DDF

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#8
When I read between the lines of Diracs white paper, I'm left with the impression that they use multiple lateral measurement points not so much for a spatial average but to identify which reflections are from side and which are from front or from back. There is a good body of evidence showing that front/back reflections have greater impact on tonal balance than from side. I would expect that Dirac then applies less or no processing to the reflections from side, but what they do is secret sauce and not published.

The reflections from side in typical rooms dont so much provide envolopment as sometimes claimed due to the short time delays of a typical residential music room. Envolopment has been studdied in detail by Griesinger https://www.google.com/url?sa=t&sou...FjAAegQIBhAB&usg=AOvVaw1JFxgmnrCWAeht7k-cbD1I

This is one area where I find even upmixed 5.1 from stereo so much more convincing than stereo. Room correction does nothing for this, but is very beneficial for removing significant peaks in the modal region, at least if you listen from one spot
 

Cosmik

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#10
That assumption isn't stated because no-one believes that.
What is the point of an in-room target curve then? How can it encapsulate 'the sound' if a human doesn't hear in the same way?
 

Cosmik

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#11
It's not theory without measurement; it's the complete opposite. Measurement without any real theory at all except "It's frequency response innit... duh!"
 

amirm

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#13

svart-hvitt

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#14
It's not theory without measurement; it's the complete opposite. Measurement without any real theory at all except "It's frequency response innit... duh!"
For generations, the goal of sound reproduction has been that of a flat and smooth frequency curve. If room EQ is about getting a flat, smooth frequency response transported to our ears, I guess we can call room EQ a means to realize that initial old goal of a speaker with a flat, smooth frequency curve. Agree?

But I am really not so certain what’s the goal of some of these room EQ packages. The goal, the hypothesis of these room EQ pagages should be stated clearer if they want to be taken seriously in a scientific setting. If their goal is somewhat vague, one should be cautious.

Take a look at this Feynman video:

 
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amirm

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#15
Toole: «2.4 “Room Equalization” Is a Misnomer».
Dr. Toole says that for the same reason I explained: that you can't fix the room. I find however that if I don't use a term like Room EQ, the topic is not understood. It is a better version than Room Correction.
 

svart-hvitt

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#17
Dr. Toole says that for the same reason I explained: that you can't fix the room. I find however that if I don't use a term like Room EQ, the topic is not understood. It is a better version than Room Correction.
The right word or term is difficult. For example, Genelec call it «room compensation», which sort of deals with the «misnomer» issue.
 

DDF

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#18
That assumption isn't stated because no-one believes that.
You mean my envelopment comment? I've seen March Audio and others make that claim here. I pointed it out because it related to Dirac's routine (as I read it) of cleverly avoiding over compensating side reflections. I think that observation was pertinent and critical to the conversation.
 

SIY

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You mean my envelopment comment? I've seen March Audio and others make that claim here. I pointed it out because it related to Dirac's routine (as I read it) of cleverly avoiding over compensating side reflections. I think that observation was pertinent and critical to the conversation.
No, not that- you got in after the comment I was referencing and before my post went up.

I was talking about this:

It is based on a vague, unstated assumption: that humans are purely frequency content analysers and that they can't distinguish between direct sound, reflections and reverberation; so as long as the contents of an FFT window more-or-less give the right proportions of 'frequency response stuff', it will sound perfect.
 

Floyd Toole

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#20
For generations, the goal of sound reproduction has been that of a flat and smooth frequency curve. If room EQ is about getting a flat, smooth frequency response transported to our ears, I guess we can call room EQ a means to realize that initial old goal of a speaker with a flat, smooth frequency curve. Agree?

But I am really not so certain what’s the goal of some of these room EQ packages. The goal, the hypothesis of these room EQ pagages should be stated clearer if they want to be taken seriously in a scientific setting. If their goal is somewhat vague, one should be cautious.

Take a look at this Feynman video:

You said:"For generations, the goal of sound reproduction has been that of a flat and smooth frequency curve". Absolutely true but . . . it only apples to electronics and to the direct sound from loudspeakers. I think you have my book and know about my JAES papers starting in the 1980s, where it has been monotonously evident that in double-blind listening tests listeners award the highest ratings to loudspeakers radiating the flattest, smoothest on-axis/listening window (i.e. direct sound) curves.

The historic problem arose decades ago when people were making simple pink-noise/RTA steady-state in-room measurements with an omni mic. They incorrectly assumed that this one curve described sound quality, and applied the "flat is right" criterion to measurements that incorporated the direct sound and all following reflections from any angle at any time. As you point out two ears and a brain know better! This mistake led to the incorrect X-curve in cinemas and in some room EQ targets. As most people know, a flat steady-state room curve, using conventional forward-firing loudspeakers, will sound excessively bright. In the cinema context they decided to roll off the highs starting at 2 kHz for the X curve (why 2 kHz? Nobody knows for certain). As pointed out in my JAES paper cited in the first post, the room curve resulting from typical forward-firing loudspeakers radiating flat direct sound, in a cinema or in a home, must tilt downward. It is physics.

I devote much of the 3rd edition of my book to this issue in the context of home audio and cinemas. Acoustically they are not fundamentally different, yet as things stand, they are incompatible. The home audio and music/broadcasting recording studio situations are complicated by existing ITU and EBU standards that specify the desirability of flattish anechoic on-axis frequency response, and then go on to require EQ to achieve flat steady-state room curves. One cannot have both at the same time. The standards are wrong. They contribute to the circle of confusion.
 
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