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Your opinion about room correctional software Virtual Instrument Plugins
Old 18th April 2010
  #31
SAC
Registered User
 

Regardless of what brand name an instrument goes by, it's claims and use are still defined by physics.

To paraphase a source:

Regardless of what instrument you use, one it has made a measurement, what can you do with it?

Herein lies the fundamental objection to processes sold commercially that claim to control a PEQ, signal delay(s) and other processes,
ALL of which can control ONLY the DIRECT signal!

If that is not clear, please read it again until it is!

Echoes, reflections, ambient signal noise, reverberation all only occur AFTER the direct sound.


It is perfectly obvious that the electronic processors adjust direct sound only since they have no way to look into the future and see what will happen IF some direct signal were released from the system. No sound system can anticipate an echo nor can it send an anti-phase signal to cancel it. This means that correct adjustment of the direct sound is still correct after an audience arrives and modified the listening environment, before it arrives and during an entrance and exit. This leaves the adjustment of the total sound field to the tender mercies of direct signal program EQ with hopefully sensitive adjustment of distortions that might mask some room effects. And this process is best done by a trained ear, and is outside of the realm of what ANY of the various magic processors claim to do.

...And to jump back to the FINAL tweaking of a room with PEQ.

AFTER all system and signal alignment, level adjustments, and room treatment is performed, it is then posible with several tools to ascertain if any of the room response exhibits a relationship of frequency amplitude and phase where the relationship of the various component superposed signals exhibit a one to one relationship (per the Hilbert Transform) and are defined to be 'minimum phase'. If such regions exist, THEN precisely controlled PEQ can be utilized to 'flatten the amplitude response while also making similar 1:1 adjustments to the phase response.

Several programs are able to evaluate the relationship of the actual frequency response amplitude and phase responses of the room for a given location with the Hilbert transformed evaluation of said relationship. If there is agreement between the two, they are minimum phase. If not, and "excess phase" exists, they are not minimum phase.

If such a minimum phase relationship exists, to the extent that such regions are defined and the anomalies fall within these regions, it is possible to apply limited amounts of PEQ.

In regions where the actual frequency response amplitude and phase are not related 1:1 by the Hilbert response (meaning that excessive phase' exists and they are not 'minimum phase') - in other words, the resultant superposed response is the result of the combination of two or more signals not aligned with respect to time, then the anomaly CANNOT be effectively addressed by any kind of EQ. This is a restriction imposed by physics, not by the particular brand of correction!

This is appropriately applied as a final step in a complete acoustical analysis and treatment process.

Various programs can analyze the response for the presence and 'extent' of exactly such a minimum phase relationships - if such regions exist. Examples are TEF and Room Control. If such regions do exist, then PEQ can be used to help address those particular issues.

But DO not think that this process is some magic cure all. It is an extremely limited additional step that provides very minor adjustment compared to much more substantial steps made previously in the process. And it is by NO means an adequate alternative.

Below one can see screen shots of such a tool.




(And the use of spatial averaging simply reduces the quality of some listening positions while marginally improving the response at others in order to achieve more mediocre seats, of which none are optimal!

This is similar to what Bose achieved with their direct-reflecting system by 'more evenly' distributing the region of destructive polar lobing and comb filtering over a larger more uniform area, rather than having a smaller 'sweet spot' and a correspondingly larger 'less than optimal' region, thus making the apparent listening region seem larger by minimizing the radical difference between good and bad and maximizing the mediocre! Whoopee! )


The bottom line: we can keep repeating the same assertions and objections based upon belief over and over, but this does not change the fundamental physics that remain the defining and, often, limiting issue! Neither belief, however fervent and sincere, nor how glossy the marketing brochure, nor how large the potential market, modify the underlying physics, as nice as one might wish that to be.
Old 20th April 2010
  #32
Gear Head
 

what's the rules in the virtual world

If you measure a signal(s) and see how it's affected in your real world situtation, if your clever enough I wouldn't like to say you can't overcome the difficulties involved in getting a piece of software to do a decent job eventually.
Old 20th April 2010
  #33
SAC
Registered User
 

So, how much time have you got???

The limitation is not the software nor how much time you have to twiddle the knobs...

The limiting problem is the time relationship between various direct and reflected signals.

And unfortunately, regarding non-minimum phase sources, changing the frequency of the direct signal via EQ, or causing small changes in phase depending upon the specific type of EQ used, affects both the direct and reflected signal and fails to remediate the time based differential existing between the multi-sourced superposed signals and the resultant error.

Thus the fundamental problem remains - although there is very good (almost a necessary) chance that you have now moved the problem around.

Its a physics problem caused by time - that quality that, according to the old joke, is that which keeps things from all happening at once - and that is precisely the problem here. Even though the phenomenon are separated by fractions of a second, they are NOT all happening at once.. heh
Old 20th April 2010
  #34
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Dange's Avatar
 

I know someone who is doing a PhD looking at critical listening in small spaces and they did mention once that use of room EQ software may have perceptual implications, i.e. possible psychoacoustic effects. By altering the sound sent to the loudspeaker, you're not allowing the speaker to do what it's designed to do - i.e faithfully reproduce the original input signal.

And yes correcting all room acoustic problems with EQ is not possible, that's just physics.
Old 20th April 2010
  #35
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Bjorn Omholt's Avatar
 

I'm a bit surprised by the attack on room correction here. Some of the best systems I've heard used DEQX:
DEQX High Definition Audio
The very best sounding systems I've heard used a combination of acoustic treatment and room correction. In these systems the room correction was set up manually and not press a button automatic magic box. The room and many places around sweetpot was measured thoroughly. Room correction was applied by many hours of listening and tweaking. And the result was in my ears quite stunning.

I've also heard room correction where I absolutely disliked the sound. So I've heard both results. But there's no doubt that it's always best to treat the room with absorbents, bass traps and diffusors first. From my experience, room correction is more then just icing the cake. In most systems in a normal living room, I would say it's necessary to achieve excellent sound. It just need to be done correctly. The fact that one has had a negative experience with room correction doesn't mean all is bad.

You probably have seen this one:
Audio Musings by Sean Olive: The Subjective and Objective Evaluation of Room Correction Products
Old 21st April 2010
  #36
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jhbrandt's Avatar
bwo,

Please don't be surprised. You have in this thread 3 other professionals that I know of & maybe more. This is a serious issue because of the subjective opinions of many. Our opinions (professional) are objective opinions. We endeavor to give facts based on test data and evidence & experience in the field.

You are absolutely correct about DEQX. But DEQX does not correct for room anomalies. It corrects via feedback from the speaker to compensate for non-linearity in the speaker/box system. Which it probable does an excellent job. Any 'room correction' that it does afterward is probably minimal.

As far as 'room' correction goes, the laws of physics still apply and like you said, "But there's no doubt that it's always best to treat the room with absorbents, bass traps and diffusors first." Which is what we are all saying here anyway. heh

If you want the psyco-acoustic effect, fine. But for a critical accurate monitoring/mixing environment, proper acoustics & acoustic control is absolutely necessary. This indeed takes thought and planning which no magic machine can do for us.

It is my hope that many who are thinking about using a program to correct their room anomalies without having to put up bass traps or reflection point control will read this thread. -- And have another 'think' coming.

Cheers,
John
Old 21st April 2010
  #37
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Rod Gervais's Avatar
 

Quote:
Originally Posted by jhbrandt View Post
bwo,


It is my hope that many who are thinking about using a program to correct their room anomalies without having to put up bass traps or reflection point control will read this thread. -- And have another 'think' coming.

What he said...... thumbsup thumbsup
Old 21st April 2010
  #38
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Bjorn Omholt's Avatar
 

Quote:
Originally Posted by jhbrandt View Post
bwo,

Please don't be surprised. You have in this thread 3 other professionals that I know of & maybe more. This is a serious issue because of the subjective opinions of many. Our opinions (professional) are objective opinions. We endeavor to give facts based on test data and evidence & experience in the field.
I hope the opinions are objective but it's hard not to think that several here sell acoustic products. But I know people here have more experience then I do and have heard many more very good sounded systems. My experiences are somewhat limited and I really haven't heard many excellent setups.
Quote:
Originally Posted by jhbrandt View Post
You are absolutely correct about DEQX. But DEQX does not correct for room anomalies. It corrects via feedback from the speaker to compensate for non-linearity in the speaker/box system. Which it probable does an excellent job. Any 'room correction' that it does afterward is probably minimal.
Here I think you're wrong. I've heard DEQX with and without room correction and the difference wasn't small. Quite dramatic. Not exactly sure what you mean by acoustic anomalities, but I believe DEQX only uses impulseresponse correction in the bass region and normal parametric EQ above. I've heard a couple room correction systems (Lyngdorf and Audiolense) that use impulseresponse correction to the whole frequency range and these sounded to my ears unatural and flat.
Quote:
Originally Posted by jhbrandt View Post
As far as 'room' correction goes, the laws of physics still apply and like you said, "But there's no doubt that it's always best to treat the room with absorbents, bass traps and diffusors first." Which is what we are all saying here anyway. heh

If you want the psyco-acoustic effect, fine. But for a critical accurate monitoring/mixing environment, proper acoustics & acoustic control is absolutely necessary. This indeed takes thought and planning which no magic machine can do for us.

It is my hope that many who are thinking about using a program to correct their room anomalies without having to put up bass traps or reflection point control will read this thread. -- And have another 'think' coming.

Cheers,
John
Yes, but for hifi system in a living room it's almost impossible to get a great frequency response alone with acoustic treatment. And room correction can also treat dips. If the room correction that I liked was completely transparent or not I don't know. What I do know is that it sounded darn good. Would it have sounded even better with more acoustic treatment? Absolutely. But one doesn't exclude the other. The link to Sean Olive also shows that several of the room correction systems was preferred over nothing in a blindtest. The one that came out worse then no correction, I believe was Audessey.
Old 21st April 2010
  #39
SAC
Registered User
 

I'm not selling ANYTHING! Nor am I interested in buying concepts that simply defy fundamental physics - concepts of which NONE have demonstrated even a cursory ability to explain, let alone 'modify'.

And NONE of them can do more than modify the direct signal from the speaker.
NONE of them can correct for ANY speaker room interaction where the relationship is not minimum phase.

And with all due respect, the notion of "impulse/response correction" is meaningless nonsense! They can not change the time relationships of the various superposed signals! By changing anything in the direct signal, you also make the same changes to the source of the reflected signals! And PEQ is ONLY effective with minimum phase relationship signals!

And "room correction" cannot fix nulls caused by the cancellation of 180 degree out of phase signals! And you notice how even you and the products continue to use the nonsensical term "room correction"? But hey, saying they can modify the direct signal doesn't sound nearly as capable or mystical.

But I do get a laugh out of products that by virtue of claiming to look at behavior with respect to time that they also think that they can change that relationship with respect to time solely by modifying the direct signal! So please, tell us how they can modify the direct signal independently of the reflected signals which originate from those identical same direct signals?

Unfortunately NONE of the manufacturers make a clear distinction in their marketing of any of the various tools - as evidenced by the myriad folks here and elsewhere who are under the impression that they do exactly what they cannot do.

And unfortunately, such techniques as averaged spatial responses and inverted feedback (even if the latency was zero!) does not correct issues of non-minimum phase superposition.

I find it amazing that only in audio do we seem to have so many folks routinely claiming to have redefined and overcome basic definitions and relationships in physics and so many folks so willing to believe in claims of their doing exactly that!

Belief is a wonderful thing. Unfortunately it is not borne out by simple physics. And none of the concepts discussed here are rocket science - although from reading the descriptions and claims they are so obfuscated and jumbled by the product literature and testimonies that they are almost incomprehensible.

So, while testimonials are impressive (and Ethan has a great presentation regarding that topic!), I have not seen nor heard one thing that addresses the basic physics. And if they wanted, they could use the same time domain analysis to show us how the basic relationships of the direct signals and specular reflections have been modified. But isn't it amazing how deafening the silence is in that regards? And how loud the emotional testimonials? But then commercials routinely rely upon impassioned testimonials instead of objective fact, as by law those who make such claims are not considered 'experts' and are considered unqualified to make actual claims of performance - thus rendering the manufacturers not liable for such claims.

But then the debate over whether one can simply EQ non-minimum phase anomalies is still alive and well here and in the audiophile realm after almost 25 years since that subject was effectively settled in the more academic realms of acoustics. So why should we expect more magical solutions to be questioned? ...And to think that it is only because modern ships have such sophisticated navigational systems that they are prevented from falling off the edge of the earth! Isn't technology miraculous?!!!
Old 21st April 2010
  #40
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Weasel9992's Avatar
 

That's true...SAC can be contentious at times (love ya man), but he's objective, no doubt about that. He also knows what he's doing. I'll also say that even though GIK sells acoustic treatment, there's no opinion that says that you should never use room correction; quite the contrary. The only caveat we put on it is that it should be used AFTER treatment and not INSTEAD of treatment. That has more to do with giving the analysis algorithms a good environment to work with so the program can be musical corrections rather than radical ones.

Frank
Old 27th April 2010
  #41
Gear Maniac
 

Hi guys i finally had time to measure my room with and without arc however i have no clue on what im looking for so i attached the files maybe some one with experience could read those graph and point out the differences
Attached Files
File Type: zip Archive.zip (436.2 KB, 38 views)
Old 27th April 2010
  #42
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jhbrandt's Avatar
AOS,

What program uses these files? .frq

Thanks,
John
Old 28th April 2010
  #43
Gear Maniac
 

Quote:
Originally Posted by jhbrandt View Post
AOS,

What program uses these files? .frq

Thanks,
John
Room Eq Wizard is the software that i used.

let me know what do you make of these results

thanks
Old 28th April 2010
  #44
SAC
Registered User
 

We cannot open them.
Old 28th April 2010
  #45
Gear Maniac
 

i will repost them as .mdat tomorrow

should i measure from 20hz to 20khz ?
Old 28th April 2010
  #46
SAC
Registered User
 

Not sure what format .mdat is, but we are not looking for data files to be convolved.

If this helps... we are not necessarily interested in opening them using the application that created them.

We simply need the final convolved display that can be opened in, for example, a Windows viewer... Files formats such as jpeg, png, etc.

Assuming the response is to analyze the room:

Freq response - linear scaling. little (1/24 octave) to no smoothing
for modal behavior we only need ~0 - 400 Hz.
Waterfall/cumulative spectral decay - the same - for each speaker, one driven at a time, the mic remaining stationary for all trials at the listening point.

Impulse response and the convolved ETC - windowed to maximize the S/N on the Y axis ('maximize the vertical display' of the data the screen with the response) displaying about 100 ms after the arrival of the direct signal.

If this is to try to prove the value of the treatment, there is much more required that I am not sure the various smaller platforms provide - such as 1:1 overlays of amplitude and phase and the ability to perform the Hilbert transform...and I suspect the 'smaller' packages do not allow for the flexibility to perform and display the various perspective manipulations that are useful. But there is little need for that - this has been done many times (on the larger more comprehensive analysis packages) and we already know the limitations.
Old 28th April 2010
  #47
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Weasel9992's Avatar
 

Quote:
Originally Posted by SAC View Post
Not sure what format .mdat is, but we are not looking for data files to be convolved.

If this helps... we are not necessarily interested in opening them using the application that created them.

We simply need the final convolved display that can be opened in, for example, a Windows viewer... Files formats such as jpeg, png, etc.
Exactly. REW gives you the option to save the plots as jpegs.

Frank
Old 9th June 2010
  #48
Here for the gear
 

Hello,

I am the author of Audiolense - one of the sound correction offerings that has been mentioned in this thread. As a starter, let me say that I don't regard digital sound correction as an alternative to acoustic treatment. You need both to achieve the best possible sound quality. But let me also say that you can do a lot more with DSP than some of the sceptics seem to believe.

SAC quoted some strong statements about sound correction and physics that are often brought forward but nevertheless incorrect.

Quote:
Originally Posted by SAC View Post
It is perfectly obvious that the electronic processors adjust direct sound only since they have no way to look into the future and see what will happen IF some direct signal were released from the system.
There is an easy way you can look into the future. It's called "impulse response measurement". It shows with very high accuracy how the speaker and room is going to modify the signal in the listening seat.

Quote:

No sound system can anticipate an echo nor can it send an anti-phase signal to cancel it.
This goes against basic textbook DSP.

In DSP, the impulse response of the speaker + room is regarded as a filter. This filter convolves with the signal that enters the speaker and creates the comb filter effects, standing waves, cancellations etc.

Any LTI system can be inverted, and speakers + rooms are to a very large degree LTI systems. Therefore, it is possible to make a digital filter that neutralises a lot of what the speaker + room does. The theoretical result will be a perfect impulse response.

The statement above also goes against existing sound correction solutions. Audiolense, Trinnov, DRC and Acourate are all capable of true time domain correction to some extent. The practical results, when healthy compromises are made are less impressive than a perfect impulse response, but one can negotiate standing waves in the bass, early reflections in the lower midrange and the phase distortion of the direct sound higher up quite effectively. The only thing worth doing with comb filter effects by means of DSP is to correct the negative impact this can have on the overall frequency balance. Usually, correction above 1 kHz is basically speaker correction and general voicing.

Quote:
If such a minimum phase relationship exists, to the extent that such regions are defined and the anomalies fall within these regions, it is possible to apply limited amounts of PEQ.
This is true in theory, as far as minimum phase equalisation is conserned.
Quote:

In regions where the actual frequency response amplitude and phase are not related 1:1 by the Hilbert response (meaning that excessive phase' exists and they are not 'minimum phase') - in other words, the resultant superposed response is the result of the combination of two or more signals not aligned with respect to time, then the anomaly CANNOT be effectively addressed by any kind of EQ. This is a restriction imposed by physics, not by the particular brand of correction!
You can do nonminimum phase time domain & frequency domain correction with FIR filters. Audiolense, Trinnov, DRC and Acourate does that.

Digital sound correction is a valid alternative when tonal balance is the main problem, whether it's a bomy bass, a depressed lower midrange, a too forward presence or whatever. At least with Audiolense you can achieve an audible and measurable time domain improvement. But the improved tonal balance is likely to be the most dominant factor. A pure frequency response correction can get you a long way - even in the finest systems. PEQ isn't precise enough to get the job done though. You need long FIR filters and a GUI that enables fine tuning of the frequency response.

With DSP, the sound can be tailor made to the preferences of the user. It will not fix room acoustics but it can maximise the performance of a given system in a given acoustic environment. Usually that means a huge step up in sound quality. Digital sound correction is not an alternative to good room acoustics when the best possible sound quality is desired. And good room acoustics isn't an alternative to good DSP either. You need both to maximise the sound quality.

Most of all DSP is an alternative and supplement to old fashioned speaker crossovers. It provides more design flexibility and less distortion on general basis. Add to that the taylor made factor and the difference in sound quality is usually very large.
Old 9th June 2010
  #49
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Ethan Winer's Avatar
 

Lightbulb

Quote:
Originally Posted by juicehifi View Post
I am the author of Audiolense - one of the sound correction offerings that has been mentioned in this thread.
Excellent, thanks for chiming in.

Quote:
it is possible to make a digital filter that neutralises a lot of what the speaker + room does. The theoretical result will be a perfect impulse response.
This is all true, with one really important caveat - the more correction you apply with DSP, the smaller the physical area you can correct will be.

--Ethan

________________
The Acoustic Treatment Experts
Old 9th June 2010
  #50
SAC
Registered User
 

Quote:
Originally Posted by juicehifi View Post

There is an easy way you can look into the future. It's called "impulse response measurement". It shows with very high accuracy how the speaker and room is going to modify the signal in the listening seat.


This goes against basic textbook DSP.

In DSP, the impulse response of the speaker + room is regarded as a filter. This filter convolves with the signal that enters the speaker and creates the comb filter effects, standing waves, cancellations etc.

Any LTI system can be inverted, and speakers + rooms are to a very large degree LTI systems. Therefore, it is possible to make a digital filter that neutralises a lot of what the speaker + room does. The theoretical result will be a perfect impulse response.
Inversion predates DSP.There is a reason it is not a default method of equalization!

And your example of the impulse response looking into the future is quaint, but hardly applicable in a complex distributed time and frequency variant environment. As one might note, the impulse response will vary with each position. And the notion that the direct signal can be modified such that it retains its 'original integrity' while also being modified to anticipate and correct for the later superposition due to both the original direct signal and any number of subsequent reflections simply has not been established. And then you have the seat next to this 'idealized spot which is worse off than before applied correction due to a modified direct signal and whatever additional filtering is imparted to correct for non-minimum phase reflections which do not correspond to the behavior just a few feet away!!

The use of DSP for limited near minimum phase low frequency correction is valid - but not at the expense of fundamental siting and room treatment. But the addressing of complex non-minimum phase site specific "room" correction is simply not a valid claim - and this claim dominates the field! In fact, to simply achieve it at a strictly defined single spot in a well controlled simple room (minus coupled spaces, complex reflections, etc. etc. etc. that define most conventional spaces!) would be an amazing feat.

And all of this is attention seems focused on equalization! If ONLY equalization were the most critical issue related to the MUCH larger issues of intelligibility, imaging, tonality!

(And this utterly ignores the larger psychoacosutical issues such as the Initial Signal Delay gaps, the termination of said ISD triggering the Haas and Henry Precedence effects, and the establishment of a well behaved, exponentially decaying diffuse soundfield! - as well as such contributing causal issues as speaker Q)

And perhaps that is the biggest disconnect regarding DSP systems - however complex. Finite impulse response (FIR) based DSP, or the use the multiple AFPs, are capable of providing an essentially flat phase response over the frequency range of from the very low frequencies up to the first break up mode of a high frequency driver in the 10 to 20 kHz frequency range. And although such a phase response can sound subtly better, the price is an exorbitant propagation delay. And yet it is still insufficient to optimally account for the variations in complex listening environments.

But then I guess we could dev0lve into discussing just how few folks' speaker systems are as they imagine and actually exhibit the controlled Q and spatial polar dispersion patterns , let alone exhibit the signal alignments between drivers that they assume and the impact on the listening experience such issues of group delay impart. ;-) (It never seems to end, does it?!? )


And while attempting to mitigate phase errors and achieve a relatively flat phase response, they do not address the spatially variant time and frequency variations of the reflected sources based upon varying boundary impedance nor the additional 'space induced' resonance and decay variations caused by such things as coupled spaces. You simply cannot do that with a single source direct signal valid for multiple listening positions!

Over the years these systems have been trotted out with all sorts of spurious marketing claims, which ironically are an insult to both the designers themselves as well as the buying public.

And it is the disconnect between the actual capabilities of DSP and the incredibly misleading claims of the marketing of such systems where the true disconnect occurs. It is a shame that too often we have these 'debates' between the technoids and not between the technoids who understand the internals and the idiotic marketing folks for whom if one claim is good, why not make it 3 or 4 or....who want to exaggerate the mystical claims regarding such technologies.

Far too much is claimed and far too little is delivered rendering the vast majority of the marketing claims simply bogus - as noted by so many of the marketing brochures depending, like TV infomercials, on subjective claims.

And funny, none of the testimonies are from folks whose association would impress the full range of the audio and acoustics community. One could start with folks like Russ Berger, Don Davis, Sam Berkow, Peter D'Antonnio, Don Keele, John Murray (of the TAO Saori DSP - ironically who do not make such exhaustive claims!), Peter Mapp, or even experts in DSP technology such as Dr. Eugene Patronis or Ron Sauro. As if they work, I suspect that most would have no qualms with endorsing something that is objectively beneficial.

But again, it would likely require the reigning in of the marketing hype to correlate with the technical realities! So its little wonder marketing eschews such avenues!

DSP offers many uses. But it is thus far unable to deliver on the exhaustive complex deliverables that are required to adequately achieve what many claim in the form of "room correction". But thus far, DSP can provide significant improvement in the direct signal as sourced from the speaker and direct signal itself.

The fundamental problem is that in a single sourced environment, you cannot address the myriad listening positions with the plethora of response signatures with DSP. DSP can indeed do many things, and the failure to acknowledge its limitations seems to be a fundamental limitation within the community as well.

And one wonders why transfer functions for multiple locations and a full array of pertinent measurements both pre and post DSP are never provided. Like magical claims of interconnects that solve all of humankind's ills that are never objectively substantiated with even something as simple as a Heyser spiral (think of it as an enhanced - more comprehensive 3 space impulse response) providing a comprehensive source to evaluate the time and frequency variate complex impedance that is the origin of source and load Z variations and the resulting 'match', few DSP claims of the nature that we are addressing EVER provide such exhaustive analysis.

And in this one regard, the 'silence' is deafening.

Bottomline, DSP can indeed do some very interesting and useful things. But it doesn't deliver on the full gamut of critical complex variables that characterize a complex listening environment.
Old 9th June 2010
  #51
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Where's that popcorn eating smilie when you need it? heh

Frank
Old 9th June 2010
  #52
SAC
Registered User
 

How come the marketing folks responsible for the spurious claims never show their face and discuss the basis for the hype that extends FAR beyond the actual capabilities of the systems????
Old 9th June 2010
  #53
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Quote:
Originally Posted by Weasel9992 View Post
Where's that popcorn eating smilie when you need it? heh

Frank




heh
Old 10th June 2010
  #54
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My argument against use of correctional software is that while the room can almost be treated as a LTI system (linear time invariant system) save for airflow, temperature fluctuation etc., the human ear simply cannot. We just do not hear like a microphone 'hears'. It doesn't act in a linear way at all
Old 10th June 2010
  #55
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It seems like many of you share the same experiences that I have with different methods of correction.

I would like to point out some issues in room impulse response correction:

1. The removal of reflections is being calculated by a processor that is fed by the signal from one microphone. The time alignment between the direct sound (correction signal) and the reflection (the reflected version of the direct sound) will never be the same for both ears since the location of the correction signal is in the speaker and the location of the reflection is not. The ears are extremely sensitive to this time alignment. If the measurement microphone is placed between the listeners ears (asuming the listener is not there at the moment) and it picks up a side wall reflection, the ears will hear:

Direct sound left ear
Direct sound right ear
Reflection left ear
Correction signal left ear
Correction signal right ear
Reflection right ear


This off course is only valid at high frequencies as the wavelengths needs to be quite short.

2. Room resonances that contributes to dips in the response curve are still resonances. The convolver method can not include the variation in impulse response that occurs when you change the duration of the signal. When the signal disappears, the level inverts (rises) before it fades. The initial dip will get bigger with longer signals, and so will the rise in level and time to fade out.

3. At low frequencies the closest surfaces to the speakers adds to the direct sound, and at very low frequencies, the room as a whole adds to the direct sound. Besides amplification and reduction, the room also contributes to the shape of the curves. If you have a resonance at 50Hz and plays back all frequencies from 45 to 55Hz, they will all sound like they are "versions" of the 50Hz tone instead of being individual tones. This is because the room contributes to the rise and fall-time of the curve and this tends to be more audible than the repeating speed of the curve. This is the same effect as you get with a bandpass subwoofer or a very high Q bass system.

This is not a shortcomming with room correction systems. It is simply a factor the correction system can not deal with.

4. The body is a large microphone. As high as 500Hz the air filled cavities of the body starts to "listen". This means basically our upper body. Around the same frequency, the body also starts to act as a tactile receiver. However, at 500Hz the audio energy in furniture and building material is very low so it is more useful to talk about a limit around 250-300Hz for tactile sensitivity. The skin and hair also pick up a lot of energy, but basically below 100-150Hz. At 50Hz and lower the hair on our head and on our skin contributes to amplify our sensitivity. This is not something we can look away from since all real life experiences are made with our body as a part of our listening device. If you expose the ears no low frequency sound at all (below 80Hz), but still exposes the body to sound energy at low frequencies, it is extremely hard for us to tell that we do not hear a thing below 80Hz. Since a dip at ear height might as well be a peak at the rest of our body, it is not very likely to hit spot on with single point correction.

5. The debate on room correction is very focused around the amount of correction, the type of correction and so on. Using single point measurements (which is the only way to do impulse response correction to a room) does not separate between loudspeaker/audio system errors and room errors. When reducing the amount of correction, the amount of loudspeaker correction is being reduced as well. Doing anechoic measurements of the speakers separately allows for at least 2-4 times the (useful) resolution as a room measurement. Our ears are also far more sensitive to direct sound errors than room effects. However, it is very hard (probably impossible with todays technology) to make precise anechoic speaker measurements from the listening position in a normal listening room, so proper correction has to take care of the speakers in a different way than the room.



An interesting debate!
Old 10th June 2010
  #56
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Quote:
Originally Posted by Yiannis View Post




heh
That's the one! heh

Frank
Old 10th June 2010
  #57
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Ethan Winer's Avatar
 

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Quote:
Originally Posted by Midgard Audio View Post
2. Room resonances that contributes to dips in the response curve are still resonances ...

... If you have a resonance at 50Hz and plays back all frequencies from 45 to 55Hz, they will all sound like they are "versions" of the 50Hz tone instead of being individual tones.
Excellent points.

--Ethan

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Old 10th June 2010
  #58
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For me this says it all"


Quote:
Originally Posted by juicehifi:

it will not fix room acoustics but it can maximize the performance of a given system in a given acoustic environment. Usually that means a huge step up in sound quality. Digital sound correction is not an alternative to good room acoustics when the best possible sound quality is desired. And good room acoustics isn't an alternative to good DSP either. You need both to maximize the sound quality.
And (for me) end of debate..........

Rod
Old 13th June 2010
  #59
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Unfortunately, it seems to be the end of the debate for everyone else as well...
Old 14th June 2010
  #60
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Quote:
Originally Posted by Midgard Audio View Post
Unfortunately, it seems to be the end of the debate for everyone else as well...
Eh...I don't know about that. I think the post Rod quoted really kind of says it all. Room correction can be a useful tool, but only when used in the the right context. That's not saying anything negative about it at all.

Frank
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