Are audio companies all involved in a huge conspiracy? - Page 22 - AVS Forum
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post #631 of 3048 Old 10-08-2012, 11:43 AM
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Originally Posted by amirm View Post

Any chance we could do away with this quest to put derogatory labels on people this way?.

I wrote earlier I don't know of another adjective that describes this specific grouping. It is derogatory, becuse the act it describes is. It's not directed at anyone specific.
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post #632 of 3048 Old 10-08-2012, 12:09 PM
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Sadly it seems that what you have learned is precisely what is wrong with online information about acoustics. It is super heavy on buying fiberglass and sticking them on the walls, and light on why. No listening tests are ever discussed. No discussion of human perception. No discussion of available research. And importantly, how inaccurate measurements in acoustics can be above 200 to 400 Hz transition frequency.

That is so wrong it has to be either an assumption or an outright lie.

In fact, the opposite is the truth, I came across discussions of all the above, and links to various papers from industry experts. There didn't seem to be any specific agenda other than to create a good sounding room and I don't have any recollection of anyone being outwardly self-serving.
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post #633 of 3048 Old 10-08-2012, 12:33 PM
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Since derogatory labels are always bad, regardless of their accuracy, I propose that we stop using the word "thief" to describe a person who steals things. Think of the stigma this derogatory label places upon people who don't think they are doing anything wrong. They are the true victims here. To protect these victims, let's instead call them "ownership transfer agents".

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post #634 of 3048 Old 10-08-2012, 12:59 PM
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Originally Posted by amirm View Post

Here is a sample from Paul Miller showing all the various jitter sources each represented by a pair of spikes to the left and right of the center axis:
i-bh66DFK-X2.png


All of these spikes were created due to timing errors for audio clock over HDMI.

False or irrelevant claim. The timing errors are traceable to mishandling of a clock signal that is internal to some digital device whose identity has been obfuscated.

The fact that the clock signal is based on a signal that entered the scene via HDMI is an true but unhelpful statement. Similar results might be obtained were the signal to arrive via other means such as a SPDIF or Toslink cable. SPDIF, Toslink and HDMI interfaces share a common relevant characteristic, which is that the digital audio clock synchronizing signal is not transmitted separately from the digital audio data.

There are really two obvious technical problems with the obfuscated device under test:

(1) The DAC in the obfuscated device lacks really good rejection of jitter in its clock.

(2) Whatever means that the obfuscated device uses to create this internal clock signal is itself flawed and does not adequately reject jitter.

Furthermore, the entire post I'm responding to is irrelevant to Goneten's question about HDMI cable quality because there are very good reasons to believe that Miller labs used as fine of a HDMI cable as they could to run this test.
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In this case the overall amount of jitter is 4.8 *billionth* of a second. These are small numbers to be sure but we see that they create distortion products that are as highs -80 db. A 16 bit system by reference, has -96 dB dynamic range. So distortion so small in time domain has caused very high (relatively speaking) analog distortion in our DAC.

The phrase relatively speaking is very relevant because there is no actual direct evidence that the jitter shown above is audible.

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BTW, earlier Arny said "If you actually believed that Amir, you would have never cited any of the HDMI jitter information from Miller labs, because it is free of information about the issue you raise below: The frequency spectrum of the jitter." Well, you are looking at the spectrum of jitter above. smile.gif The only thing is that he chops off the spectrum at +- 3.5 Khz and I would like to see all of it. But the spectrum is there.

However, transforming the spectrum shown in the provided obfuscated equipment test into the spectrum of the jitter is not trivial at all. The information is there but making it useful would take a lot of work.
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So the notion that a digital transmission only transmits digital data simply is not correct.

Straw man argument. I know of nobody on this forum who has actually made this claim. If Amir can't cite an example of such a thing happening on this forum in the recent past then he is just making up issues to argue with himself about. ;-)
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post #635 of 3048 Old 10-08-2012, 01:24 PM
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Ok, this interesting, luxury items is where high audio makes money smile.gif

If you look at LOUIS VITON plastic bags made in China that cost $5 to make and are sold for $1000 that is what I call a massive rip off!

So speaking about electronics yes when one considers speakers at 100,00 dollars, the dealer. Buys them for 50,000. The manufacturer' cost is $12,500 so in the end the consumer pays for gigantic profit margins.

That is why I always negotiate prices and usually get nice discounts, I don't mind paying for R&D. I will never put my money into expensive cables as they are all made of copper unless I want silver, but I d'on't see the point in that wink.gif

Now having said that, money is made to enjoy oneself and if it please someone to buy cables at $5,000 a foot and they have the mean, we'll enjoy the jewelry!
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post #636 of 3048 Old 10-08-2012, 01:40 PM
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Ha, but unlike cables, the purse vendor doesn't claim to make the items in it better somehow.
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post #637 of 3048 Old 10-08-2012, 02:12 PM
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If you look at LOUIS VITON plastic bags made in China that cost $5 to make and are sold for $1000 that is what I call a massive rip off!
No, it's not a ripoff. When someone pays $1000 for that bag, she knows exactly what she is buying, and has decided it's worth it to her. You may think it's a foolish purchase, but she does not.

It would be a ripoff if someone charged you $1000 for a knockoff of a Louis Vuitton bag. It would be a ripoff if they managed to disguise the fact that it had a hole in the bottom. But things aren't ripoffs just because they have high margins.

If you can't explain how it works, you can't say it doesn't.—The High-End Creed

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post #638 of 3048 Old 10-08-2012, 04:51 PM
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Originally Posted by Ethan Winer View Post

You are more outraged at my writings about acoustics than the claims of wire vendors? Really Amir? Better tell that to the dozens of magazines that published my articles about acoustics, and the thousands of people who have thanked me over the years for helping them to achieve better sound quality in their recording studios and listening rooms. And you don't call your relentless attacks on me "going after him personally and calling him a snake oil vendor?" You should run for public office because you are comfortable with the same types of lies we hear every day from politicians.
Amir, I ask you yet again: Where are the blind tests for preference that back up the claims on your web site? Until you provide those, you are in no position to be attacking me. In fact, you are worse than what you accuse me of just for the sheer hypocrisy.
I did that recording in stereo using a Zoom H2 portable recorder.
--Ethan

Time and time again I see this charge of 'hounding', 'attack', 'persecution'....c'mon, I think we need to settle down a bit and stay calm.

TBH, ALL that is/has happened is some received wisdom has been questioned. A perfectly rational thing to happen. In many cases the reaction is far more telling than the question.

As but one example of a way to step back and view w\hat is happening is to reframe the viewpoint. Argue all you want about whether cables make a difference or not, well I for one don't think that is the relevant point.

WHY does this aftermarket cable industry exist? Because the myth is that 'there are ways to improve the sound that only the ears can detect which just so happens to also prove the concept that measurements do not tell us all'. By examining the WHY we get to the point, rather than look at the myriad, shallow surface phenomena. We also enter the realm of caps, different brands of resistors as well as cables if you follow me. Stop paddling on the surface and dive a little.

So, in the very same vein it can be useful to step away from the veneer and examine what lies beneath it and in THIS analogous case we are examining the truism that 'absorbing FR' is always beneficial for all or the best thing to do. That comes from things like 'as it is based on measurements and science we can trust it more and have no need to examine it'...prob very bad summation there so help me out! Anyways, even here we are conflating two very different things, there is prob nothing wrong with the data BUT we are taking that one step further and extending it as being explanatory of preference.

At the very least we need to be wary of where that might fall down?

I don't get (tho I can understand it) this persecution gig.

Think about it, someone who is totally and completely confident in their knowledge and conclusions, well it would be water off a ducks back. (To me at least) when I see myself reacting in this way, well it is a great thing to spot cause more often than not it is an insight into my OWN poorly understood areas of my own stance. A very valuable diagnostic technique so that I can better understand my own views.

If I can say so, as another example I think you (ethan) have an undue reliance on things like comb filtering in your thinking. (I say this as it being a another possible insight into where we can be led astray). In the most part, I reckon comb filtering is more a measurement artifact than any real explanation of what we hear. AND, I raise it not to cause conflict or have an argument, but because it is intrinsically interesting to me and (I think) a worthwhile path to explore. After all, IF I am right in any degree then it has it's own value to it being cleared up not to mention any 'false practices' (if I can phrase it that way) that have resulted from it.

To start that ball rolling, how is it that you generate these comb filtering graphs?
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post #639 of 3048 Old 10-08-2012, 05:10 PM
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Time and time again I see this charge of 'hounding', 'attack', 'persecution'....c'mon, I think we need to settle down a bit and stay calm.
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I don't get (tho I can understand it) this persecution gig.
That's because you're not the one exercising a vendetta here. Someone else is. We're not talking about you. You raise some reasonable questions, although raising them in a thread about snake oil is, I think, a misjudgment on your part, because it suggests an equivalence that is undeserved (and that I suspect you don't really mean, although the other guy does).
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That comes from things like 'as it is based on measurements and science we can trust it more and have no need to examine it'...prob very bad summation there so help me out!
If you want to claim that somebody is misusing or misreporting science in his advertising, I think it's incumbent on you to present the evidence. It's not Ethan's job to help you hang him. If you don't even know what has been said, you don't have anything to stand on at all.

If you can't explain how it works, you can't say it doesn't.—The High-End Creed

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post #640 of 3048 Old 10-08-2012, 06:16 PM
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Originally Posted by mcnarus View Post

That's because you're not the one exercising a vendetta here. Someone else is. We're not talking about you. You raise some reasonable questions, although raising them in a thread about snake oil is, I think, a misjudgment on your part, because it suggests an equivalence that is undeserved (and that I suspect you don't really mean, although the other guy does).

Yeah, I guess I misphrased the point. I DO understand that feeling when it is directed 'at us' so on that hand it is perfectly understandable. But I feel very much that (at least when I) get that feeling it can mean there IS some vague point you instinctively get that your own position might not be as strong as you first thought. Kinda a definitional thing perhaps, if you feel defensive then there probably IS a reason to be defensive about it, equally if there is no need to feel defensive then you wouldn't. If that made sense which I doubt.

But your point about it being in a snakeoil thread is perhaps the most important. THAT is the false equivalence I feel. Snakeoil only comes about because the underlying 'science' is not understood or ignored. IF there is some underlying science about room treatment that is not known or being ignored (the science in this case dealing with preference) then to me, even whilst admitting the distasteful connotations associated with the term snakeoil, they are basically from the same pea pod.

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If you want to claim that somebody is misusing or misreporting science in his advertising, I think it's incumbent on you to present the evidence. It's not Ethan's job to help you hang him. If you don't even know what has been said, you don't have anything to stand on at all.

Well here it is, just stated in a different way. I am NOT out to hang him! eek.gif I am however extremely interested in these areas of conflict, they are direct indicators of where the shifting or unstable ground lies. One part of the evidence you ask of me is (without digging the quotes up) is Ethans beliefs he may have found the reason of cable differences....he sits in one position and hears the sound, get's up and changes the cables and then sits in a very slightly different position, and hears a different soundfield which is 'proven' by the different comb filtering as shown by very slightly moving the mic. Well, to me, that is 'not even wrong' to quote Pauli.

That represents to me a misreading of measurements (I could be wrong, just so's it's clear, but certainly worth clarifying no?). It's all well and good to have measurements, but you can get yourself into a pretty pickle if there is not an equivalent understanding of them.
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post #641 of 3048 Old 10-08-2012, 07:24 PM
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Originally Posted by terry j View Post

I feel. Snakeoil only comes about because the underlying 'science' is not understood or ignored.

I see a couple of logical flaws here. Your use of "only" precludes other possibilities, and your use of "the underlying science" implies the existence of such. I'm not sure if there's a broad consensus, but from my perspective, a major class of "snake oil" products are products for which claims are made with no underlying science whatsoever to back them up. This situation falls outside your "only" clause and is not a rare occurrence by any means.

To equate that with leaving out information regarding the potential subjective improvement of retaining sidewall reflections is a false equivalence. There have been some heated discussions on AVS involving studio folks who insist that "accuracy" (however problematic this concept is when applied to room response) should be the be-all and end-all characteristic one seeks in the measured data. Such people are also Ethan's customers, so he must pursue a path that does not alienate either faction. It seems to me that omission may be the most prudent approach for someone like Ethan in that position.

Edit: Another class of snake oil products comes to mind, related to your "underlying science" phrase. In this case, "underlying" should mean not only "relevant", but also "demonstrated to be the actual cause" of the phenomenon being observed. In some snake oil scenarios, some science is presented, but the results may not be relevant to the situation. An example of this is Ben Duncan's measurements of RF behavior of power cords as part of an attempt to get a UK vendor out of legal hot water. Assuming proper power supply design, the measured differences he found are irrelevant.
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post #642 of 3048 Old 10-08-2012, 11:58 PM
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Originally Posted by rock_bottom View Post

I see a couple of logical flaws here. Your use of "only" precludes other possibilities, and your use of "the underlying science" implies the existence of such. I'm not sure if there's a broad consensus, but from my perspective, a major class of "snake oil" products are products for which claims are made with no underlying science whatsoever to back them up. This situation falls outside your "only" clause and is not a rare occurrence by any means.

Haha, half the time why my posts are long and boring is usually due to all the caveats I find I have a habit of doing, seems in this case not enough! smile.gif Having said that, not too sure I agree with you completely, nor if it makes too much difference anyway.

"I can fly, and if you send me a cheque I can teach you the arcane secret lost thru the ages". We'd prob agree that falls into your definition of snake oil (or at least a false claim) but there IS science beneath it. You can't. "No science to back them up" is still science, and falls completely into how I meant the phrase I used. I mean, there is nothing about the higgs boson and it's field that will make cables sound better....but just wait. It will be interesting to see how long it takes biggrin.gif

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To equate that with leaving out information regarding the potential subjective improvement of retaining sidewall reflections is a false equivalence.

For the umpteenth (?) time, I am making no such equivalence. Maybe the problem is the title of the thread? It would be a perfectly fine thing to explore if it were in a thread called 'what are some examples of possible 'everyone knows' that might actually be untrue'?
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Edit: Another class of snake oil products comes to mind, related to your "underlying science" phrase. In this case, "underlying" should mean not only "relevant", but also "demonstrated to be the actual cause" of the phenomenon being observed. In some snake oil scenarios, some science is presented, but the results may not be relevant to the situation. An example of this is Ben Duncan's measurements of RF behavior of power cords as part of an attempt to get a UK vendor out of legal hot water. Assuming proper power supply design, the measured differences he found are irrelevant.

I covered that above, yeah precisely the type of thing I had in mind. Not only 'relevant' as you said, but also denied by science (I can fly). I guess here we should also point out that 'preference' whilst still open to the scientific method is maybe a 'softer' science than these hardcore examples??
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post #643 of 3048 Old 10-09-2012, 05:11 AM
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Originally Posted by terry j View Post


So, in the very same vein it can be useful to step away from the veneer and examine what lies beneath it and in THIS analogous case we are examining the truism that 'absorbing FR' is always beneficial for all or the best thing to do. That comes from things like 'as it is based on measurements and science we can trust it more and have no need to examine it'...prob very bad summation there so help me out! Anyways, even here we are conflating two very different things, there is prob nothing wrong with the data BUT we are taking that one step further and extending it as being explanatory of preference.
At the very least we need to be wary of where that might fall down?

If one ignores some significant facts then it might be possible to compare room acoustics upgrades to cable upgrades. In my thinking the three most important facts are:

(1) Cable upgrades generally have no audible effects at all. I've done the measurements, I've done the tech analysis, I've done the DBTs and so have others, and a statement this global seems warranted. There are no reasonable amounts of better cables that will change the sound of people's audio systems. If anything, expensive cables can make things worse but they are generally benign.

(2) Room acoustic changes if broad enough, do at least have audible effects. I'm being a little over careful here because products such as the Totem Beak (http://www.stereophile.com/content/totem-acoustic-beak ) count in some people's minds as acoustical tuning devices. It is also true that some people hang up a few square feet of acoustic foam in 450 square foot listening rooms and expect a major difference. There are ineffective or only marginally effective acoustic tuning products of a considerably more serious nature. I've had this experience for myself.

(3) The room, even if designed by an acoustical expert (remember, both Earl Geddes and David Clark are close personal friends of mine and I've spent hours listening to a wide range of recordings in both of their listening rooms) generally seems to need some acoustical tuning after initial set up to sound its best. Given that most audiophiles aren't acoustical experts, and a lot of audio systems are in rooms that were designed for other purposes, there seems to be a lot of room for acoustical tuning in the real world. IME most but not all rooms start out with excessive reflections and inadequate absorption.
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post #644 of 3048 Old 10-09-2012, 07:57 AM
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Just curious Arny/Ethan - do you at least agree that HDMI jitter levels such as those measured from a couple receivers a few pages ago (~4000ns I believe) eat into the theoretical dynamic range/SNR of 16-bit 44kHz material?
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post #645 of 3048 Old 10-09-2012, 08:44 AM
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Originally Posted by rock_bottom View Post

Such people are also Ethan's customers, so he must pursue a path that does not alienate either faction. It seems to me that omission may be the most prudent approach for someone like Ethan in that position.

I gladly alienate and offend people in both camps - recording types and audiophiles. biggrin.gif

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post #646 of 3048 Old 10-09-2012, 08:50 AM
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Originally Posted by kromkamp View Post

Just curious Arny/Ethan - do you at least agree that HDMI jitter levels such as those measured from a couple receivers a few pages ago (~4000ns I believe) eat into the theoretical dynamic range/SNR of 16-bit 44kHz material?

You mean picoseconds. But yes, when it's that high it can exceed the noise floor of 16 bits. However, the spectrum matters too, with some frequencies being more audible than others as per Fletcher-Munson. This graph is from The Art of Digital Audio by John Watkinson. It shows the amount of jitter noise you can expect at various frequencies, with the noise floor of various bit depths as a reference.

jitter_noise.gif

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post #647 of 3048 Old 10-09-2012, 09:59 AM
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Originally Posted by kromkamp View Post

Just curious Arny/Ethan - do you at least agree that HDMI jitter levels such as those measured from a couple receivers a few pages ago (~4000ns I believe) eat into the theoretical dynamic range/SNR of 16-bit 44kHz material?

Going back a few pages ago to post 631, I believe the amount of jitter mentioned there was 487 psec, which is far, far less than the 4 usec mentioned above.

If memory serves, 4 usec jitter would be characteristic of an analog turntable or tape machine.

My first problem is that just the amount of timing change due to jitter does not adequately define SNR:

http://www.eetimes.com/design/analog-design/4010006/Understand-analog-digital-converter-clock-jitter-and-why-you-should-care

SNR = 20 × log [1/(π × input frequency × Tj)]

where Tj = jitter time

Referencing Ethan's jitter/SNR chart which agrees with the equation given above:



I find that 487 psec or 0.487 nsec jitter is always above the 16 noise floor (optimistically given above as 96 dB) when the signal frequency is in the audio band.

Furthermore, I would expect that the actual SNR of a typical recording would be more like 75 dB, which provides an additional margin of safety against audible problems.
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post #648 of 3048 Old 10-09-2012, 11:00 AM
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Just curious Arny/Ethan - do you at least agree that HDMI jitter levels such as those measured from a couple receivers a few pages ago (~4000ns I believe) eat into the theoretical dynamic range/SNR of 16-bit 44kHz material?
Why speculate? Since we have AVRs with high measured jitter via HDMI, it should be fairly easy for anyone truly concerned with this issue to conduct a good DBT and address the question directly. Simply compare an AVR with high HDMI jitter to one with low hitter (or use a non-HDMI connection). Compared to testing room treatments, this exercise would be trivial.

The fact that people who insist this is a problem nonetheless refuse to demonstrate that it's a problem should tell you something.

If you can't explain how it works, you can't say it doesn't.—The High-End Creed

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post #649 of 3048 Old 10-09-2012, 11:06 AM
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Going back a few pages ago to post 631, I believe the amount of jitter mentioned there was 487 psec, which is far, far less than the 4 usec mentioned above.
I believe we've seen measurements as high as 7600 ps. If I'm reading Ethan's chart correctly, that suggests at least potential audibility for artifacts above about 10 kHz. I wouldn't bet the rent money on it, though.

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post #650 of 3048 Old 10-09-2012, 11:22 AM
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Right (sorry about the units mix-up). If we say 4ns of jitter that threshold lands somewhat below 10kHz on Ethan's graph (assuming that graph is logarithmic) So if the belief is that artifacts that demonstrably can be present in a 16-bit signal but are claimed to be not audible, does it then follow that all greater than 16-bit formats are similarly not an improvement over 16-bit? I'm just curious who believes that this level of jitter is not audible, but who also believes that formats like SACD/DTS-HD/etc are an improvement over CD?
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post #651 of 3048 Old 10-09-2012, 11:52 AM
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Originally Posted by mcnarus View Post

I believe we've seen measurements as high as 7600 ps. If I'm reading Ethan's chart correctly, that suggests at least potential audibility for artifacts above about 10 kHz. I wouldn't bet the rent money on it, though.

The devil is in the details which in this case is the most significant jitter frequency. I think we may be able to refine the situation somewhat with some reasonable assumptions.



The far and away most energetic jitter frequency shown in the graph above is around 100 Hz. This jitter seems to relate to a framing or blocking system that is probably common to many HDMI interfaces of a certain era, now several years ago. It is an obvious situation that has probably been dealt with by now.

Nevertheless the 16 bit threshold at 100 Hz, according to the chart (originally brought to the discussion by Ethan) in my previous post, is someplace around 100 ns or 100,000 ps. IOW, 7600 ps is probably still way below the 16 bit threshold and therefore not audible.
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post #652 of 3048 Old 10-09-2012, 12:07 PM
 
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Originally Posted by Arnyk 
If there were audible timing problems, error correction would not help at all. Error detection and correction first and foremost eliminates tics and pops, which one finds out about when there are undetected and uncorrected errors in digital audio signals.

So error correction can only sort out issues that we can't hear? If we can hear them then correction couldn't possibly help. Am I understanding you correctly?
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post #653 of 3048 Old 10-09-2012, 12:25 PM
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So error correction can only sort out issues that we can't hear? If we can hear them then correction couldn't possibly help. Am I understanding you correctly?

Partially Correct. Because if error correction could handle it, it would have been handled. If there is an error and you don't hear it. Well you don't hear it and never knew there was a problem.

It's like stability and traction control in a car. It could help you avoid an accident. But then if you are in an accident, it didn't. The error was so gross as to overcome the mechanism.

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So error correction can only sort out issues that we can't hear?
In a way. When error correction can handle the errors, then the results are no audible problem.
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If we can hear them then correction couldn't possibly help.

If the error is so large that the error correction can't help, then we may hear a problem.

Error correction deals mostly with numerical errors in the digital data. There are other kinds of errors, such as timing problems. They are often handled in other ways.
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Quote:
Originally Posted by arnyk 
There are other kinds of errors, such as timing problems. They are often handled in other ways.

I think I'm a little confused. I assumed (incorrectly) that error correction was used to prevent timing issues from becoming audible. If you hear it, correction can't help. But from the above (as I understand it) you are saying that error correction handles issues not related to timing. So error correction can't help with timing at all? What then helps with timing, if not error correction? Sorry, I'm not terribly well versed in this, but I am interested to learn more. Thanks for the help.
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NM

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post #657 of 3048 Old 10-09-2012, 02:11 PM
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Earlier I hinted about other tutorials on Ethan's site which runs counter to published science. This one took a while to prepare as I wanted to run some personal tests to demonstrate the same point in addition to quoting the literature. If you go to Ethan's site, you see a decidedly cold reception to electronic correction/EQ. The back up for that is in sentences like this: ". Modal ringing - an extended decay at some, but not all, bass frequencies - is just as damaging as a skewed low frequency response, and EQ cannot reduce ringing. Only bass traps can reduce ringing." It goes to say others disagree but that he has not seen it work over a "large area." Not sure how that is related to it not correcting ringing.

As a way of background, when you play your speakers in your room, so called "room modes" or resonances serve to change the frequency response of the speaker. So much so that you can measure your speaker in an anechoic chamber all you want. The response in the room will be determined largely by the room at frequencies below transition (200-400 Hz). When we measure the frequency response in this region, we see pretty wild swings, as much as 30 db. Every 10 db perceptually causes us to think something is twice as loud. So 30 db is pretty bad. None of this is in disagreement. What is in disagreement is what happens in "time domain." Time domain is what it says. It shows you what happens to a signal one sample after the other. Room resonances manifest themselves as "ringing" in that if you excite the room with a pulse, the room keeps signing the tune even after the note is gone. Time domain resonances can be shown to be audible below transition frequencies. A base note that lasts longer than it is supposed to will sound different than one that is not. Ethan in his statement says that electronic EQ is half a solution if it only works in frequency domain and can't impact time domain ringing. Naturally he positions acoustic products as the full solution even though he acknowledges in his article that as frequencies go down, they can get pretty unwieldy.

Back to the point of contention, Ethan backs his point of view with a test of Audyssey auto EQ. He shows before and after "waterfall' displays which show the combined frequency response and time, indicating no change in time domain. Note however that his thesis summary is not limited to what Audyssey does but the entire domain of electronic EQ. This is the graph he shows for the sub which is the scenario I tested also:

art_audyssey2.gif

So I set out to test this phenomenon in a controlled environment. I put a sub in a corner, turned off the crossover and used Room EQ Wizard to run a sweep. I generated a waterfall display with carefully set parameters to make the output visible *and* correct. There are a lot of pitfalls here. If you want to read about that in general, and this test specifically, click on the first link in this search: https://www.google.com/search?q=site%3Awhatsbestforum.com+Acoustic+Measurements%3A+Understanding+Time+and+Frequency&rlz=1C1SNNT_enUS374US375&oq=site%3Awhatsbestforum.com+Acoustic+Measurements%3A+Understanding+Time+and+Frequency&sugexp=chrome,mod=0&sourceid=chrome&ie=UTF-8

This is what we get:

i-RR3TCwS-L.png

The back wave shows our frequency response which is not very pretty with peaks and valleys as one would expect. Front to back shows how long the frequencies are lasting. This display is rather compromised and can look different with different settings in REW. Again, the link I provided earlier describes this in detail. For the purposes of this exercise though, we can live with it.

Eyeballing for a peak, I chose 53 Hz as a frequency to go after to pull down. I also made a wild guess on how wide to make my parametric EQ. All the testing by the way was done on a JBL SDEC-4500 Synthesis EQ which gives me plenty of these filters with very fine grain control of frequency and “Q.” This is what we get now if I overlay this EQed correction in green over the earlier brown measurement of no EQ:

i-z7Cg55m-L.png

The blue line going through the graph from front to back is set at 53 Hz. We see right away that the frequency domain correction at 53 Hz has been accompanied by respective change in time domain in reduction of ringing. The faded brown shows what used to be there which is now missing in green.

In the article I show addition of filters one at a time but for brevity, let’s jump forward and look at what happens with four filters in play:

i-tfbz347-L.png

Like clockwork each change in frequency domain, bringing a peak down has resulted in the time domain (back to front) improvements. The blue line for example is for 110 Hz and we see that it has done its job.

I don’t think it gets any clearer that what Ethan says in his online article does not hold water. Ringing is changed for the better. It really had no choice though smile.gif. The science says it should. Room resonances with respect to peaks in a room are what we call “minimum phase” phenomenon. Such a system has a phase response which tracks its amplitude (Hilbert transform). In that sense, if you fix the amplitude with a filter with reverse response to the resonance, the correction applies to the phase just the same and yu get correction in both frequency and time domains. The literature tells us the same things. Here is Dr. Toole:

” Using equalization to reduce the bump also attenuates the ringing so both problems are solved simultaneously.”

Dr. Toole shows the following measurements:

i-2MGmS4B.png

He does the work with both coarse and fine grain EQ and in both cases we see a reduction in time domain ringing that accompanies the flatter frequency response on the left.

Peter. Craven and Michael Gerzon in their AES DSP conferences titled, “PRACTICAL ADAPTIVE ROOM AND LOUDSPEAKER EQUALISER FOR HI-FI USE” come to the same conclusion and back it with measurements as I have done:

i-mKkg4Dd-X2.gif

Per Rubak and Lars Johansen in their AES paper draw on the above work and opine the same way:

” As pointed out by Craven & Gerzon [5], room equalizers based on Digital Signal Processors are able to reduce the reverberation time considerably, even if we only use minimum-phase equalizers. Our preliminary test results are in agreement with this important potential for DSP based equalizers. Therefore we have put focus on objective test methods concerning the improvement of the room acoustics using equalizers.

So you have my test data plus three authoritative sources all contradicting Ethan’s statement. Listening tests to my quick optimizations confirmed the same. I played guitar strings on the sub alone and it was rewarding to hear every single pluck with EQ, which was smeared without before. So subjective evaluation follows objective analysis.

Here is one of Ethan competitors arriving at the same results as I have in a real room/project: http://www.acousticfrontiers.com/Room-Correction-Services.html

"Below: waterfall chart showing before / after results from application of room correction at 25Hz and 50Hz by Acoustic Frontiers. Notice that both the peaks in the frequency response and ringing in the time domain have been eliminated. These measurements were from a 9 seat dedicated home theater that we calibrated - see the full case study."

Nyal has provided the above data to Ethan on this forum yet we still read what is written on his site.

Where did Ethan go wrong? If you look at the Audyssey correction, you see that little of what it did matched what I have done here. Its “after” EQ still has pretty ragged peaks so not much correction was applied. Some peaks were taken down others raised. The angle of presentation also makes it hard to see what the back frequencies are doing as there is a dominant one in front. So the fact that correction didn't come about in time domain is natural: it didn't work in frequency domain either. So this is not a good example to use to make a point, nor is it reasonable to have it represent all classes of EQ systems as Ethan has done. He goes on to lament about this class of products and manufacturers:

” Unfortunately, the popular audio press gushes uncritically over products like these, printing press releases as fact and never actually testing the validity of manufacturer claims. The appeal of a small electronic device that claims to replace large and visually imposing acoustic panels is undeniable. But wishful thinking does not make it so! Even the vendors themselves offer no real proof that their products work as claimed. “

While he is somewhat justified in saying that companies like Audyssey don’t provide much visibility into how well their system works, others such as Harman have done so in publishing both papers and listening tests results. Here is test data for a number of EQ systems I reference in my article, http://www.madronadigital.com/Library/BassOptimization.html:

Room%20Correction%20Preferences.png

In this test, two EQ systems did worse than no EQ. The Audyssey on the right and Anthem next to it. The yellow is Lyngdorf followed by the highest scoring results on the left by Harman. The green is optimized for multiple seats and blue for a single. All three results outperform doing no EQ (orange). You can read more about this test here: "The Subjective and Objective Evaluation of Room Correction Products," Sean E. Olive, John Jackson, Allan Devantier, David Hunt, Harman International, 127th Convention, Audio Eng. Soc. Preprint 7960. http://seanolive.blogspot.com/2009/11/subjective-and-objective-evaluation-of.html

The excellent multi-seat results from Harman (which is deployed in “ARCOS” for the JBL Synthesis EQ I used) shows that we can achieve excellent performance across a wide area unlike what Ethan implied. Indeed EQ done right is a powerful technique. Combine that with multiple subs and SFM (explained in my article) and you may not need any low frequency acoustic products.

Hopefully you now see why I am so unhappy with the tutorials on Ethan’s site. No matter which way you dice it, they steer people away from science and always toward one thing: buy more acoustic products. Every mistake I find results in sales of more acoustic products. I get that he is in that business. Nothing wrong with promoting his products in the best light possible. My issue is him providing these articles as often as he does as guiding people new to this field on how acoustics works. I am great fan of him when it comes to simplifying concepts as he does but we can’t lose track of what the science really says. And in these major points it simply does not say what he says. Many of these other techniques that he either ignores on his site or gives backhanded compliment are quite essential and powerful in optimizing the sound in our rooms. You can't ignore them. They are great problem solvers as a subwoofer is much easier hidden in the room as compared to 17 bass traps!

As you see, it takes a lot of work to write these posts. I do them because I have passion around getting the right info out there. I am so frustrated that I wasted so much time on mistaken notions as read online and Ethan's articles. It is time that we direct people to the right data and not cover up the hole in the purse as was said here. wink.gifsmile.gif

Amir
Founder, Madrona Digital
"Insist on Quality Engineering"

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post #658 of 3048 Old 10-09-2012, 02:45 PM
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Ethan:

What do you think about claims made on this URL:

http://www.madronadigital.com/Showroom/HomeTheater.html
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post #659 of 3048 Old 10-09-2012, 03:10 PM
 
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It is time that we direct people to the right data and not cover up the hole in the purse as was said here. wink.gifsmile.gif
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“yes but… is it audible?” As unfair as it might be, I am going to punt that question.
First thing first, amirm, it's time you answer the question instead of dodging, oops, I mean punting that question. So, what's the answer?
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post #660 of 3048 Old 10-09-2012, 03:31 PM
 
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Never mind.
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