svart-hvitt
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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?
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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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.
