Debate Thread: Scott's Hi-res Audio Test - Page 20 - AVS Forum
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post #571 of 2920 Old 06-13-2014, 05:52 PM
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Originally Posted by amirm View Post
I am trying to "minimize" a debating tactic that tries to dismiss any information that is not in your favor with the same line over and over again: "where is your DBT?"
No, this post tries to dismiss any information that is not in your favor with the same false claims over and over again.

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I am presenting measurements.
Audio measurements are irrelevant and even deceptive unless there is a reliable correlation between the measurements and sound quality.

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And I am presenting system architecture.
Who cares if it does not produce better sound quality?

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And I am presenting quotes from AES saying there is a fidelity problem with HDMI.
False claim. The actual statement from am AES committee report (not a refereed technical paper) is:

"HDMI receivers must derive audio word clock from the video pixel clock, commonly resulting in very high jitter that affects quality and can be audible."

The above statement contains a vague statement that misleads many people. It uses the phrase "high jitter". What is high jitter? Ironically jitter has been commonly characterized using minuscule units of measurement such as picoseconds that allow the use of very high numbers. This is misleading and deceptive.

The above statement does not say that there is always a fidelity problem with HDMI. It says that there can be a fidelity problem with HDMI.

Since I'm seeing posts that exemplify the same logical problem over and over again, please let me explain it to one and all like I would explain it to an ignorant young child:

It is a true statement that airplanes can crash and kill all of the passengers and crew aboard. Therefore, only suicidal people fly in airplanes, right?

Not true!

While airplanes airplanes can crash and kill all of the passengers and crew aboard, they do it so infrequently that airplane travel is one of the safest forms of transportation that is available today. Perfectly sane, non-suicidal people ride in airplanes because while it is an absolutely correct truth that they can crash and kill all of the passengers and crew aboard, they do it very infrequently.

It is an absolute truth that there can be a fidelity problem with HDMI or just about any other kind of audio technology. However, we still use all of those forms of audio technology because the fidelity problems are very frequently not audible.

It is an absolute truth that there can be a fidelity problem with power amplifiers or just about any other kind of audio technology. However, we still use all of those forms of audio technology because the fidelity problems are very frequently not audible.

It is an absolute truth that there can be a fidelity problem with CD players or just about any other kind of audio technology. However, we still use all of those forms of audio technology because the fidelity problems are very frequently not audible.

It is an absolute truth that there can be a fidelity problem with streaming audio or just about any other kind of audio technology. However, we still use all of those forms of audio technology because the fidelity problems are very frequently not audible.

It is an absolute truth that there can be a fidelity problem with digital players or just about any other kind of audio technology. However, we still use all of those forms of audio technology because the fidelity problems are very frequently not audible.

Does everybody get it now? Just because it can be perfectly accurately said that there can be fidelity problems, this is not proof that they are always manifest as audible problems.
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post #572 of 2920 Old 06-13-2014, 06:01 PM
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Originally Posted by amirm View Post
I don't see DBTs as a replacement for measurements.
Straw man argument. DBTs and measurements provide different kinds of information. Measurements do not prove the existence of an audible problem unless there is a generally agreed upon understanding that a certain measurement always indicates the existence of an audible problem.

It is a fact that it has already been established on this forum that no measurements have been presented that come within several orders of magnitude of indicating audibility in accordance with the best scientific knowledge that we have about the threshold of audibility of FM distortion (Zwicker and Fastl 2007).
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post #573 of 2920 Old 06-13-2014, 06:46 PM
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Who is this nonengineer you're talking about?
Given that he does not seem to understand the role of cost/benefit analysis in engineering, might that be the person making the statement?
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post #574 of 2920 Old 06-13-2014, 07:22 PM - Thread Starter
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Originally Posted by Chu Gai View Post
A more careful reading from the AES does not say there is a fidelity problem, rather that there can be audible consequences with HDMI. If they'd said 'there are audible consequences' then I would agree with your words.
I am unclear as to how you are interpreting that. Here is what they said again:

HDMI, the point-to-point connector required for BR and HD video, has excellent bandwidth and an Ethernet data link (HDMI 1.4), but lacks an audio clock. HDMI receivers must derive audio word clock from the video pixel clock, commonly resulting in very high jitter that affects quality and can be audible. Some high end receivers address the jitter and many companies are researching it but current solutions are expensive and uncommon.

They correctly identify that the problem is extracting digital audio clock from a not so stable video clock. They then go on to say the consequence "commonly" is audibility issues.

In my opinion, an audio clock would not have fixed the problem, nor a good idea in general. An audio clock would have made the job easier but still, is the wrong solution. The *right* solution is not keep duplicating this broken architecture from S/PDIF of having the source be the timing master instead of the destination (DAC). While at it, they should have made the source asynchronous, i.e. a pure data pump. That is how a computer science/networking expert would have designed it. Those people are in short supply in AV committees so they cooked up another synchronous design with the source in charge.

Look again how much better the performance of *identical* hardware is when you put the target in charge:



This is again the Pioneer AVR with PQLS mode turned on, on the right. Put the source in charge and you get the mess on the left. So there is no question that HDMI design is faulty making good performance something that takes far more design expertise than it should have been.

This is why Paul Miller's test data from products on sale in 2008/2009 match my testing end of 2012. Added experience and later generation of HDMI silicon did not ease the pain.

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Pity they didn't look to put a rough range of jitter that was the danger zone.
How would they predict the jitter range for every product in the market?

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post #575 of 2920 Old 06-13-2014, 07:56 PM
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Originally Posted by amirm View Post
I am unclear as to how you are interpreting that. Here is what they said again:

HDMI, the point-to-point connector required for BR and HD video, has excellent bandwidth and an Ethernet data link (HDMI 1.4), but lacks an audio clock. HDMI receivers must derive audio word clock from the video pixel clock, commonly resulting in very high jitter that affects quality and can be audible. Some high end receivers address the jitter and many companies are researching it but current solutions are expensive and uncommon.

They correctly identify that the problem is extracting digital audio clock from a not so stable video clock. They then go on to say the consequence "commonly" is audibility issues.
Serious English comprehension problem noted. The quote text says that "high jitter" is a "common result" (note - what is high jitter? Is it the size of a bread box or a house?) (how often does a "common result" occur? - every day, every week, every month?) They go on to say that the vaguely quantified high jitter "...can be audible...." which is again very vague. IOW it can be audible or it may not be audible - who knows?

To shed some light I took some data from this test result:

I found that the largest HDMI jitter artifact was @90 Hz and had an amplitude of about -115 dB referenced to a 1 KHz test tone. This turns out to have a modulation index of 3.55656 E-06 where Zwicker and Fastl (2007) say the just detectable modulation index is about 3.0. IOW most definitely not audible by about 6 orders of magnitude!
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post #576 of 2920 Old 06-13-2014, 08:28 PM
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Amir, I'm not disputing the higher jitter numbers with HDMI or that it can be significantly lowered using approaches like Pioneer. Nor do I think anyone participating or reading this thread is challenging that finding.

The AES group largely says the same thing. My focus is over the verb CAN. They must have some idea of what jitter levels constitute a danger zone. They're fvcking scientists not hack analysts talking about the missing Malaysian jet! Look, I realize there's not a single magic number and that people hear differently. But they must have some idea even if they take it from the study by Benjamin and Gannon. Then if they are of the opinion that they'd like to see it one or two orders of magnitude lower, that's cool with me. But they need to put some kind of face on this jitter otherwise it's just wishin' and a hopin'.

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post #577 of 2920 Old 06-13-2014, 11:16 PM
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Originally Posted by amirm View Post
I am unclear as to how you are interpreting that. Here is what they said again:

HDMI, the point-to-point connector required for BR and HD video, has excellent bandwidth and an Ethernet data link (HDMI 1.4), but lacks an audio clock. HDMI receivers must derive audio word clock from the video pixel clock, commonly resulting in very high jitter that affects quality and can be audible. Some high end receivers address the jitter and many companies are researching it but current solutions are expensive and uncommon.

They correctly identify that the problem is extracting digital audio clock from a not so stable video clock. They then go on to say the consequence "commonly" is audibility issues.

In my opinion, an audio clock would not have fixed the problem, nor a good idea in general. An audio clock would have made the job easier but still, is the wrong solution. The *right* solution is not keep duplicating this broken architecture from S/PDIF of having the source be the timing master instead of the destination (DAC). While at it, they should have made the source asynchronous, i.e. a pure data pump. That is how a computer science/networking expert would have designed it. Those people are in short supply in AV committees so they cooked up another synchronous design with the source in charge.

Look again how much better the performance of *identical* hardware is when you put the target in charge:



This is again the Pioneer AVR with PQLS mode turned on, on the right. Put the source in charge and you get the mess on the left. So there is no question that HDMI design is faulty making good performance something that takes far more design expertise than it should have been.

This is why Paul Miller's test data from products on sale in 2008/2009 match my testing end of 2012. Added experience and later generation of HDMI silicon did not ease the pain.


How would they predict the jitter range for every product in the market?
http://www.madronadigital.com/Librar...stortions.html

"Because we ignored masking, this may set too high a bar relative to our ability to hear such non-linear distortions. So if you like, you can derate them some. But don’t go too far. It is very hard to build a credible case for example that thousands of picoseconds of jitter as we usually get over HDMI is inaudible. The analysis I just provided shoots way too many holes in that line of reasoning. My personal target is a few hundred picoseconds.."

amir,
How do you arrive at the the personal target? "A few hundred picoseconds?"
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post #578 of 2920 Old 06-13-2014, 11:27 PM
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It takes about 2 ns of random jitter to degrade the output to about a 12-bit noise floor (about 74 dB).

The argument can be made that signal-dependent (deterministic) jitter is easier to hear, and I think that is likely, but I have no idea what the threshold of audibility is for it, especially with a musical source instead of test tones.

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post #579 of 2920 Old 06-14-2014, 05:35 AM
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It takes about 2 ns of random jitter to degrade the output to about a 12-bit noise floor (about 74 dB).

The argument can be made that signal-dependent (deterministic) jitter is easier to hear, and I think that is likely, but I have no idea what the threshold of audibility is for it, especially with a musical source instead of test tones.
The above statement seems to conflate signal-dependent and deterministic jitter when in fact they can be and often are independent. Much deterministic jitter is caused by modulation of the audio signal by spurious noises inside the AVR such as power line noise. In optical players it is possible for electrical noise and surges from the power supply due to operation of optical servos to be the source of such modulation. The potential sources of this sort of thing form an almost endless list but they are typically addressed well enough to render all related forms of jitter to below everybody's audibility.

While much has been made of signal-dependent jitter due to S/PDIF and interconnecting cables interacting with the audio signal, the more common causes we see today appear to be due to the non-audio properties of the signal such as data block sizes and arrival times.

The best source that I know of for information about the threshold of audibility for FM distortion (AKA jitter) is Zwicker and Fastl (2007) which I've posted here several times. I'm not encouraged to post it again and again because I've posted it before and nobody seems to pay any attention to it. Also the forum seems to have changed its procedures for posting pictures in such a way to make doing so far more difficult.

I've also set up some .wav files with variable amounts of jitter starting with unmistakable and ending with inaudible that involves the same jitter frequencies as we see in AVRs, involving both sine waves and music. Just download, plug into FooBar2000 and ABX. I've published links to them several times but I see zero signs of their usage.

Again, there appears to be zero interest in anything but ignoring the relevant facts, whether by authoritative and recognized scientific references or by means of their own personal experience. Instead people seem to want to wander around muttering nonsense and acting like its all over their heads, I guess.

So anybody who "has no idea" apparently has preserved themselves in that state by means of well practiced ignorance bordering on intellectual sloth. Either that, or they don't believe in Science and/or personal experience. When a strong proponent of high end audio pseudo science acts this way to avoid admitting his past serious mistakes, I get it. When people blunder around apparently pretending that they have no options, I don't.
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post #580 of 2920 Old 06-14-2014, 05:42 AM
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It takes about 2 ns of random jitter to degrade the output to about a 12-bit noise floor (about 74 dB).
Ironically the dynamic range of most audio recordings is worse than that.

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The argument can be made that signal-dependent (deterministic) jitter is easier to hear, and I think that is likely,
It seems to me that this is more than likely. It is readily observable when it is observable at all. IMO, one failing of many studies of the audibility of jitter is that they have started out with the jitter too small to hear. Common sense says that if you want to study the audibility of something, first you have something that can be heard. Too much work seems to have been done at or below the threshold of hearing for this sort of thing, which contrary to popular belief is easily knowable. I've even posted it here.

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but I have no idea what the threshold of audibility is for it, especially with a musical source instead of test tones.
Music is full of distractions and masking sounds, so of course the threshold of hearing for jitter of any kind with music playing is much higher than what one obtains with pure sine waves, or even silence which is relevant to some kinds of jitter. Some kinds of music can mask unbelievable amounts of jitter.
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post #581 of 2920 Old 06-14-2014, 06:24 AM
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I was trying to put some context around the magnitude of jitter, not completely explain or define it. I certainly agree there are many sources of jitter both random and deterministic, and that signal-dependent jitter is but one flavor of deterministic jitter. You did a great job of explaining that, IMO. I would have said or added noise from all the digital processing inside the box, not just power-line noise, which is usually fairly low (though once you get below 80 dB anything is very hard to suppress, as I know from trying to design 100 - 140 dB DNR radar and communication systems). In my world we deal with quite a number of different types of jitter, but I felt an in-depth discussion wasn't warranted. I tend to shy from absolutes thus all my qualifiers. Actually, I did not even think to bring up the myriad types and causes here, I was thinking about the comments about hundreds of ps of jitter mattering or not. I think the answer is "it depends".

For the record, regarding your jitter files, I did similar things a long time ago just so I could see the impact of various jitter (and distortion) when added to a signal, so have not felt a strong need to download your samples. An interesting exercise is to add the same amounts to single tones, two tones, multitones (I used five spaced over the audio range, amplitudes following the F-M curves), and a few musical samples. It can be humbling, at least it was for me and my ears of clay, to know what the jitter/distortion you have added sounds like, and still not be able to pick it out of a multi-tone or musical sample.

I (and many others) have often said a lot of folk would be shocked if they knew the amount of added processing to most recordings, and the actual dynamic range.

I don't think we are on different sides of this one, Arny, though Amir has provided a wealth of interesting data. As usual, for me the question of audibility is always the elephant in the room, and I have not done enough listening (nor really care to, no time for a lengthy test series) to contribute to that.

On engineering trades, for decades I was an analog IC design engineer focused on SOTA R&D designs. One of my co-workers said about advanced R&D (and perhaps much of engineering) "cost, performance, schedule -- pick two, settle for one!" I have always tried to do my best but the are always constraints. I designed 16-bit DAC years ago that settled in <35 ns. It was used in e-beam systems for IC fabrication and it met spec, but was not the sort of thing you'd find in a CD player back then -- far too much power, far too costly. It took me as long to test it and prove its performance as it did to design it.
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post #582 of 2920 Old 06-14-2014, 06:25 AM
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Originally Posted by arnyk View Post
Quote:
Originally Posted by DonH50 View Post
It takes about 2 ns of random jitter to degrade the output to about a 12-bit noise floor (about 74 dB).
Ironically the dynamic range of most audio recordings is worse than that.
That's likely the reason why ASHIHARA et al. (Detection threshold for distortions due to jitter on digital audio, Acoust. Sci. & Tech. 26, 1 (2005)) come to the conclusion that:
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detection threshold for random jitter added to program materials is several hundreds ns even for well-trained listeners under their preferable listening conditions. According to Benjamin and Gannon, sinusoidal jitter as small as 30ns (r.m.s.) might be detectable under a certain condition. Considering these results, the maximum acceptable size of jitter would be the order of ns.
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post #583 of 2920 Old 06-14-2014, 08:19 AM
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I noticed the SNR of the ARC SP20 ($9k preamp) phono stage as measured in Stereophile was 55/58 dB for the left and right channels... Unweighted and wideband, the line stage SNR was about 70 dB, and bandlimited to the audio band it was about 79 dB. I expected better, but an interesting insight into what a top manufacturer considers required for SNR. Of course there are other factors than SNR, and this is not directly related to jitter, but speaks to the dynamic range our components have.

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post #584 of 2920 Old 06-14-2014, 08:23 AM - Thread Starter
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Originally Posted by UndersAVS View Post
http://www.madronadigital.com/Librar...stortions.html

"Because we ignored masking, this may set too high a bar relative to our ability to hear such non-linear distortions. So if you like, you can derate them some. But don’t go too far. It is very hard to build a credible case for example that thousands of picoseconds of jitter as we usually get over HDMI is inaudible. The analysis I just provided shoots way too many holes in that line of reasoning. My personal target is a few hundred picoseconds.."

amir,
How do you arrive at the the personal target? "A few hundred picoseconds?"
Don answered this but I will provide more detail.

The metric is an engineering one that says if we have a 16 bit DAC, how low does its distortions need to be to equal the noise level of that DAC. Undithered 16-bit signal has a noise floor of about -96 dbFS relative to 0 db reference. We can work backward and determine what sinusoidal jitter we can have that has an amplitude distortion spikes at -96 dbFS. Using 20 KHz as the maximum frequency of interest, the math tells us the jitter amplitude has to be no more than 500 picoseconds or 0.5 nanoseconds.

Note that we can hear through noise. So the above metric does not assure inaudibility of the distortions. On the other hand as noted, real music may mask jitter. Then again distortions that we see are not a single jitter tone but many such tones as my measurements and that of Paul Miller show. So the actual value is pretty complex to determine. If we still insist on a single number, then the above value is a decent metric we can use to determine if our system is well implemented.

As a fun exercise, if we want to have distortions that are below 20 bit DAC, the jitter value shrinks to just 30 picoseconds! If we up the sampling rate to 96 KHz and attempt to reproduce all of its spectrum, the jitter spec now sinks down to just 10 picoseconds. If we now boost the resolution to 24 bits for "24 bit/96 KHz" the jitter spec becomes just 1 picoseconds!!!

The above numbers are computed using math and analysis of the amplitude of jitter sidebands. So the computation is quite precise and accurate. The notion then "why would I worry about picosecond jitter specs when audio is such low frequency" is put to rest. You absolutely need such low values of jitter if you are going to advertise that your DAC is say capable of 24-bit/96 KHz as just about any AVR today says.

This the math if you are interested:



Don, you did a similar analysis in WBF Forum. Did yo use Matlab and compute the actual values without the above approximation? And at any rate, can you post the link to it for people to read your well written article on it?

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post #585 of 2920 Old 06-14-2014, 08:41 AM
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In Amir's work, he found receivers to occupy one tier with processors and DACs further down although with with such a limited sample size, especially for the last two, it's a bit premature to adopt that segmentation.

Ought we not be looking for even worse levels of HDMI jitter? Maybe they exist in HTIB's or maybe laptops. If we arbitrarily say that HDMI jitter in receivers is likely not audible then maybe it likely is in other devices.

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post #586 of 2920 Old 06-14-2014, 09:22 AM - Thread Starter
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Originally Posted by Chu Gai View Post
In Amir's work, he found receivers to occupy one tier with processors and DACs further down although with with such a limited sample size, especially for the last two, it's a bit premature to adopt that segmentation.
Well, the "poor" rating is not dependent on how many or which devices tested. If there is no filtering of audio band jitter frequencies, then they are poor performers in that regard.

You could argue whether -60 db or -70 db is "best" but the overall message remains the same relative to above.

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Ought we not be looking for even worse levels of HDMI jitter? Maybe they exist in HTIB's or maybe laptops. If we arbitrarily say that HDMI jitter in receivers is likely not audible then maybe it likely is in other devices.
Laptops are not receivers of HDMI input so you can't use them in this regard. I don't have any HTIBs. Do they have HDMI inputs?

On the topic of laptops, here is another interesting measurement from my article. You see two graphs there: both are measured using the S/PDIF interface (NOT HDMI) on the great performing Mark Levinson 502 Processor:



What is the difference between the two graphs? Simply plugging in my HDMI cable caused those new distortion spikes in amber! Let me repeat: I am not using HDMI as the input. I am still measuring S/PDIF. The mere act of plugging in the HDMI cable degraded the S/PDIF performance.

What is the problem? HDMI couples the two systems electrically allowing noise to get transmitted from source to target. This is happening on a device with superb HDMI performance. By the way, once I knew what this distortion looked like, I could find it on other HDMI devices at the same frequency. So clearly this is source induced which in this case is my laptop that was generating the signals.

This makes the nature of noise/jitter over HDMI a very complex situation. You can't just judge an AVR by itself but as a combination with the source. Likewise any listening test will by definition show results for one set of devices and potentially not others. More data point is needed (with other sources) to see the extent of this problem.

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post #587 of 2920 Old 06-14-2014, 09:30 AM
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Originally Posted by DonH50 View Post
It takes about 2 ns of random jitter to degrade the output to about a 12-bit noise floor (about 74 dB).
It seems pretty clear that quantities of FM distortion measured in amounts of time don't correlate well at all with its audibility, and on a number of different grounds.

So what is better? Zwicker and Fastl use Modulation Index, and this seems to be much more than just an arbitrary choice on their part.
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post #588 of 2920 Old 06-14-2014, 09:40 AM
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Originally Posted by amirm View Post
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Originally Posted by Chu Gai View Post
In Amir's work, he found receivers to occupy one tier with processors and DACs further down although with with such a limited sample size, especially for the last two, it's a bit premature to adopt that segmentation.
Well, the "poor" rating is not dependent on how many or which devices tested. If there is no filtering of audio band jitter frequencies, then they are poor performers in that regard.

You could argue whether -60 db or -70 db is "best" but the overall message remains the same relative to above.

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Originally Posted by Chu Gai View Post
Ought we not be looking for even worse levels of HDMI jitter? Maybe they exist in HTIB's or maybe laptops. If we arbitrarily say that HDMI jitter in receivers is likely not audible then maybe it likely is in other devices.
Laptops are not receivers of HDMI input so you can't use them in this regard. I don't have any HTIBs. Do they have HDMI inputs?

On the topic of laptops, here is another interesting measurement from my article. You see two graphs there: both are measured using the S/PDIF interface (NOT HDMI) on the great performing Mark Levinson 502 Processor:



What is the difference between the two graphs? Simply plugging in my HDMI cable caused those new distortion spikes in amber! Let me repeat: I am not using HDMI as the input. I am still measuring S/PDIF. The mere act of plugging in the HDMI cable degraded the S/PDIF performance.

What is the problem? HDMI couples the two systems electrically allowing noise to get transmitted from source to target. This is happening on a device with superb HDMI performance. By the way, once I knew what this distortion looked like, I could find it on other HDMI devices at the same frequency. So clearly this is source induced which in this case is my laptop that was generating the signals.

This makes the nature of noise/jitter over HDMI a very complex situation. You can't just judge an AVR by itself but as a combination with the source. Likewise any listening test will by definition show results for one set of devices and potentially not others. More data point is needed (with other sources) to see the extent of this problem.
Circuit design is obviously not the above author's strong suit.

The first relevant fact is that HDMI equipment is very aware as to whether its inputs or outputs are attached to any other piece of HDMI equipment. This takes negligible intelligence on the part of the equipment due to the design of the interface.

The second relevant fact is that the various subsystems in a piece of portable equipment such as a laptop try to conserve energy by shutting down all circuitry is that not actually needed.

So it is highly probable that the HDMI circuits in the laptop weren't even powered up until the remote HDMI equipment was attached.

Thirdly, various subsystems in a highly integrated piece of equipment such as a laptop may interfere and propagate interference to each other in poorly designed equipment.

So simply plugging a HDMI input to the HDMI output of the laptop triggered a fairly straightforward series of events that resulted in some of the design compromises in the laptop to become apparent as increased jitter in the S/PDIF output of the laptop.
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post #589 of 2920 Old 06-14-2014, 09:46 AM
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Originally Posted by DonH50 View Post
I noticed the SNR of the ARC SP20 ($9k preamp) phono stage as measured in Stereophile was 55/58 dB for the left and right channels... Unweighted and wideband, the line stage SNR was about 70 dB, and bandlimited to the audio band it was about 79 dB. I expected better, but an interesting insight into what a top manufacturer considers required for SNR. Of course there are other factors than SNR, and this is not directly related to jitter, but speaks to the dynamic range our components have.
Here is a picture of the inside of a SP20:



Your attention may be drawn to a number of bottle-like components running the width of the equipment. No further explanations seem necessary, especially to those of us who actually tried to design and build audio gear based on them.

BTW any noise measurement that is not presented with information about the measurement bandwidth is by definition faulty. "Wideband" does not suffice. Not your doing Don, but don't put too much credibility in people who stumble at this point.
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post #590 of 2920 Old 06-14-2014, 09:53 AM
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Quote:
Originally Posted by Chu Gai View Post
In Amir's work, he found receivers to occupy one tier with processors and DACs further down although with with such a limited sample size, especially for the last two, it's a bit premature to adopt that segmentation.
The first thing to consider about Amir's work is that it is based on a number of false premises that are clear in this document:

http://www.madronadigital.com/Librar...stortions.html

Quote:
Ought we not be looking for even worse levels of HDMI jitter?
Don't need to look very hard, if one is willing to not fall into the trap of thinking that only HDMI jitter is significant. Two sources of greater amounts of jitter are as follows:

(1) Loudspeakers, with 2-way speakers being worse than 3 way speakers for example.

(2) Any recording that was produced using analog tape, The end product may be a SACD, but the fairly massive amounts of jitter inherent in analog tape recorders is built into every track unless forcibly removed.


Quote:
Maybe they exist in HTIB's or maybe laptops. If we arbitrarily say that HDMI jitter in receivers is likely not audible then maybe it likely is in other devices.
I doubt that there is a HTIB that is within an order of magnitude as being as afflicted by jitter as the two sources I just mentioned. We all use them pretty frequently.
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post #591 of 2920 Old 06-14-2014, 10:05 AM
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Hi Amir,

Last time I posted a link to WBF I got a warning. I've done it since without problem, not sure what the actual guidelines are. At any rate the list of topics is at http://www.whatsbestforum.com/showth...-s-Tech-Series Note the articles are more or less "hand waving" for engineers but (hopefully) technically accurate (if incomplete) and written such that with a little head scratching and return to HS math most folk can follow them.

I used Mathcad for most of the analysis, might be some Matlab sprinkled in, plus maybe a little HSPICE or TopSpice (don't actually remember). I used the IEEE ADC Standard for definitions, test conditions and analysis (STD-1241, also see the older STD-1057 that the newer builds upon). There are various equations around but most (all I found with a quick search) are the same once you wade through some algebra. There are a couple of fundamental derivations of quantization noise: one using a linear or sinusoidal approximation between lsb's (steps) and expectation functions; the other uses Bessel functions that is more rigorous (and a bear to wade through -- I had to help review it when it was part of a student's PhD dissertation). Fortunately at the end of the day they do agree...

I did several things through the course of the various sampling threads, from simple equations to models and transistor-level simulations that provided empirical results. Since I was not actually looking at jitter sidebands I never implemented the equations you provided above on the WBF threads AFAIK -- though I have used those in other places (not audio). For the audio articles mostly what I did was use a mathematical model of an ADC or DAC (developed over years of research) to generate samples with the desired impairments (I can add most anything, including various jitter types, white noise, phase noise, signal modulation for power/clock/etc. coupling, nonlinearities, etc.) The model has been used to correlate real-world data converters to my simulations so I am pretty comfortable with it. For jitter I used it to verify the simpler equations matched what I expected.

This is one of those subjects that gets horribly complicated very fast, and one of those things I tend to shy away from just because I feel I need to write a book or nothing. The last time I really dove into various audio distortion mechanisms was a long time ago. None of the fundamentals have changed, but I do not have the sample files I created (really wish I did, it was a lot of effort!) nor ready access to audio test equipment that I had then. Somehow our 40 - 100 GHz test equipment seems to poop out below a few MHz , and while we have DSOs will do the job, they are very low resolution (100 GS/s DSOs do not generally use high-resolution ADCs). the other major reason to shy away is I simply do not recall the results of all my tests (which involved a host of other people listening to various samples as well). My gut says 10's of ns or even more is probably inaudible on the vast majority of real-world source material (music and movies) but I am not willing to state that without actually running some tests.

Also for the record, the tests way back then (5 - 10 years ago plus many more back in the 1980's) were mostly "sighted" for me in that I always knew what I had. I was trying to prove things to myself and started with something I knew I could hear, then moved to different material and lower levels to see where I could no longer tell. If anything my bias was towards lower levels causing problems. I later was able to create a random CD by letting my test program randomly place files on the disc that I then waded through in order. I looked at the files after the test to see how I did. Something anyone could do today, except you'd stream the files instead of burning a CD.

The tests involving others was technically not double-blind since I knew the files. I used a random number table to randomize the files and each was run at least twice (in random order). I used CDs and tape (my long-gone 1/2" studio machine). Ultimately I found the CD more reliable; tape distortion tended to mask too much detail. I tested anywhere from a few minutes (whomever had time in the store when I asked) to several hours. The basic procedure was to present the listener with a badly-distorted file, a clean file (no intentional added distortion/noise), and then play the sequence of test files. Their instructions were to say if the present cut (file) was better or worse than the previous. Not the most rigorous of tests, but I was just curious to see what sort of results I got from a pseudo-scientific test. Naysayers are welcome to run their own tests. I had several "random" CDs and additional ones that tried to determine just how low the distortion could get. It was somewhat source-dependent, natch, but I also found variations from day to day even with the same listener. Setting up and running such tests is an enormous effort and consumes an immense amount of time. I was fortunate to have the time and an understanding (encouraging) boss and listeners (victims).


Edit: Several posts added whilst I was typing, sorry. This was in response to Amir's questions several posts up.

I have and do use modulation index as well as several other metrics when appropriate. While jitter can in some cases be considered FM distortion, I do not generally treat it as such because there are so many components to it. Every time I go down this rabbit hole I lose; it takes a lot of effort to really understand jitter, I am not claiming to be some all-knowing expert, and the effort to explain it and then defend whatever credibility I have left is not worth it to me. I am just glad my career does not depend upon Internet forums, where you can be defending your simplifications to a PhD in one post and a high-school student or dedicated audiophile of many years the next, all of whom "know" the right answer and have plenty of time to show the world what an idiot I am and how much more they know. I have a wife, kids, and a dog; I do not need their help for that.

OTOH, I learn a lot and enjoy seeing the information exchange here and on other fora. Fortunately I help moderate a trumpet forum so when I get fed up arguing jitter and power cords I can go moderate debates on mouthpieces and bell material. Or just go practice, or read a book while listening to some music...

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley

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post #592 of 2920 Old 06-14-2014, 11:43 AM
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Quote:
Originally Posted by DonH50 View Post
Last time I posted a link to WBF I got a warning. I've done it since without problem, not sure what the actual guidelines are. At any rate the list of topics is at http://www.whatsbestforum.com/showth...-s-Tech-Series Note the articles are more or less "hand waving" for engineers but (hopefully) technically accurate (if incomplete) and written such that with a little head scratching and return to HS math most folk can follow them.
Usual problems - characterizing jitter as a digital domain-only problem, and nothing I can hang my hat on about audibility.
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post #593 of 2920 Old 06-14-2014, 11:46 AM - Thread Starter
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Don, thank you so much for the thoughtful and honest reply. Your modesty is a breath of fresh air in a testosterone driven forum.

On the topic of how everything gets debated, in the heat of the HD DVD and Blu-ray battle where I was fielding dozens of people grilling me every day, someone said: "this is like someone being on witness stand and being questioned for two years straight!"

Speaking of HD DVD vs BD, those discussions make the ones we have look elementary. They actually shut down that subforum a couple of times for days. This made news by itself! Here is one of them: http://www.cnet.com/news/format-war-...own-avs-forum/

Format war fanboys shut down AVS Forum
After posters have resorted to physical threats from Blu-ray and HD DVD zealots, the popular AVS Forum community site has had to completely shut down the Blu-ray and HD DVD section of its site for the week.


I personally got an implied death threat in PM (forum owners were kind enough to suspend that poster), and many other personal remarks that put this discussion to shame.

Participation in anything sensitive here goes beyond a hobby and becomes a part-time or even full-time job! This is how bad it gets. The other day when the forum was down and they were switching back to Vbulletin software, I get on and see the usual intermission slide. Look down and yet again I am being quoted!



I am pretty close to adding "forum addict" to my list of jobs on my business card.

I do enjoy it though. It pushes me to learn more and see if I can properly explain what I know. All the measurements that I post came because Arny said in a post that since Pall Miller had done his HDMI measurements that all must be better due to advances in semiconductors so that data is "obsolete:"

Quote:
Originally Posted by arnyk View Post
As usual Amir you are avoiding the point which is that any competent digital receiver is supposed to resolve any likely data timing issues that arise. If certain obsolete products didn't do this, that must be one reason why improved models were produced.

Again Amir you seem to have no up-to-date technical measurements of the HDMI performance of AVRs that are currerntly on the market as new products.
So I thought he may be right. There is a newer generation of HDMI transceivers and subsystems every couple of years so I should test and report back. I had no expectations of how they all would perform. I gathered all the devices that I had and could borrow from work and made my measurements. As you have seen, there is no improvement at all since Paul Miller did his measurements in 2008/2009. It is the opposite of the say that squeaky wheel gets the oil. In this case there has not been enough of a "squeak" as to get mass market vendors to deal with this issue properly.

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post #594 of 2920 Old 06-14-2014, 12:12 PM
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Don't modesty may be symptomatic of a low-T condition.

"I've found that when you want to know the truth about someone that someone is probably the last person you should ask." - Gregory House
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post #595 of 2920 Old 06-14-2014, 12:49 PM
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This stuff is now comical.

That's it! No more HDMI.

I ain't afraid of no ghosts... but now I gots 'da jitters.
And I have nothing against testosterone if you know how to use it properly.

(note the smiley is included so everyone knows it's a joke... )

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post #596 of 2920 Old 06-14-2014, 01:28 PM
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Quote:
Originally Posted by arnyk View Post
Quote:
Originally Posted by DonH50 View Post
Last time I posted a link to WBF I got a warning. I've done it since without problem, not sure what the actual guidelines are. At any rate the list of topics is at http://www.whatsbestforum.com/showth...-s-Tech-Series Note the articles are more or less "hand waving" for engineers but (hopefully) technically accurate (if incomplete) and written such that with a little head scratching and return to HS math most folk can follow them.
Usual problems - characterizing jitter as a digital domain-only problem, and nothing I can hang my hat on about audibility.
There are several threads on jitter that show SNR loss and distortion added with random and deterministic jitter. I'll leave it to others to decide what their threshold of objectionable noise and distortion might be. Not one of the basic jitter threads treats it as a digital-only problem, the whole point is to show what happens at the output of a DAC (or input of an ADC).

Edit: I am talking about the Jitter 101 and 102A/B/C threads on WBF.

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley

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post #597 of 2920 Old 06-14-2014, 02:29 PM
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Quote:
Originally Posted by arnyk View Post
Quote:
Originally Posted by DonH50 View Post
I noticed the SNR of the ARC SP20 ($9k preamp) phono stage as measured in Stereophile was 55/58 dB for the left and right channels... Unweighted and wideband, the line stage SNR was about 70 dB, and bandlimited to the audio band it was about 79 dB.
any noise measurement that is not presented with information about the measurement bandwidth is by definition faulty. "Wideband" does not suffice. Not your doing Don, but don't put too much credibility in people who stumble at this point.
All the wideband, unweighted S/N ratios published in Stereophile are measured over the full <10Hz-500kHz bandwidth of my Audio Precision SYS2722. This is routinely mentioned in my testing, just not in the case of the Audio Research SP20 review.

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post #598 of 2920 Old 06-14-2014, 02:48 PM
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Quote:
Originally Posted by Kees de Visser View Post
Quote:
Originally Posted by arnyk View Post
Quote:
Originally Posted by DonH50 View Post
It takes about 2 ns of random jitter to degrade the output to about a 12-bit noise floor (about 74 dB).
Ironically the dynamic range of most audio recordings is worse than that.
That's likely the reason why ASHIHARA et al. (Detection threshold for distortions due to jitter on digital audio, Acoust. Sci. & Tech. 26, 1 (2005)) come to the conclusion that:
Quote:
detection threshold for random jitter added to program materials is several hundreds ns even for well-trained listeners under their preferable listening conditions. According to Benjamin and Gannon, sinusoidal jitter as small as 30ns (r.m.s.) might be detectable under a certain condition. Considering these results, the maximum acceptable size of jitter would be the order of ns.
And for those who aren't totally fluent in orders of magnitude:

1 nanosecond = 1000 picoseconds

so:

30 ns = 30,000 ps

100 ns = 100,000 ps

'several hundred' ns = 'several' x 100,000 ps

This, perhaps, puts warnings about HDMI/gear that inject 'thousands of picoseconds' of jitter, into perspective. Some more exactitude on the word 'thousands' would seem to be important there (and type & spectrum of the jitter)

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post #599 of 2920 Old 06-14-2014, 04:40 PM
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Quote:
Originally Posted by amirm View Post
Don, thank you so much for the thoughtful and honest reply. Your modesty is a breath of fresh air in a testosterone driven forum.

On the topic of how everything gets debated, in the heat of the HD DVD and Blu-ray battle where I was fielding dozens of people grilling me every day, someone said: &quot;this is like someone being on witness stand and being questioned for two years straight!&quot;

Speaking of HD DVD vs BD, those discussions make the ones we have look elementary. They actually shut down that subforum a couple of times for days. This made news by itself! Here is one of them: http://www.cnet.com/news/format-war-...own-avs-forum/

Format war fanboys shut down AVS Forum
After posters have resorted to physical threats from Blu-ray and HD DVD zealots, the popular AVS Forum community site has had to completely shut down the Blu-ray and HD DVD section of its site for the week.


I personally got an implied death threat in PM (forum owners were kind enough to suspend that poster), and many other personal remarks that put this discussion to shame.

Participation in anything sensitive here goes beyond a hobby and becomes a part-time or even full-time job! This is how bad it gets. The other day when the forum was down and they were switching back to Vbulletin software, I get on and see the usual intermission slide. Look down and yet again I am being quoted!



I am pretty close to adding &quot;forum addict&quot; to my list of jobs on my business card.

I do enjoy it though. It pushes me to learn more and see if I can properly explain what I know. All the measurements that I post came because Arny said in a post that since Pall Miller had done his HDMI measurements that all must be better due to advances in semiconductors so that data is obsolete:
Quote:
Originally Posted by amirm View Post
Guys let's be nice to each other and remain focused on technical topics please. Thanks.
I see...
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post #600 of 2920 Old 06-14-2014, 07:21 PM
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Quote:
Originally Posted by amirm View Post
Don, thank you so much for the thoughtful and honest reply. Your modesty is a breath of fresh air in a testosterone driven forum.

On the topic of how everything gets debated, in the heat of the HD DVD and Blu-ray battle where I was fielding dozens of people grilling me every day, someone said: "this is like someone being on witness stand and being questioned for two years straight!"

Speaking of HD DVD vs BD, those discussions make the ones we have look elementary. They actually shut down that subforum a couple of times for days. This made news by itself! Here is one of them: http://www.cnet.com/news/format-war-...own-avs-forum/

Format war fanboys shut down AVS Forum
After posters have resorted to physical threats from Blu-ray and HD DVD zealots, the popular AVS Forum community site has had to completely shut down the Blu-ray and HD DVD section of its site for the week.


I personally got an implied death threat in PM (forum owners were kind enough to suspend that poster), and many other personal remarks that put this discussion to shame.

Participation in anything sensitive here goes beyond a hobby and becomes a part-time or even full-time job! This is how bad it gets. The other day when the forum was down and they were switching back to Vbulletin software, I get on and see the usual intermission slide. Look down and yet again I am being quoted!



I am pretty close to adding "forum addict" to my list of jobs on my business card.

I do enjoy it though. It pushes me to learn more and see if I can properly explain what I know. All the measurements that I post came because Arny said in a post that since Pall Miller had done his HDMI measurements that all must be better due to advances in semiconductors so that data is "obsolete:"

Quote:
Originally Posted by arnyk View Post
As usual Amir you are avoiding the point which is that any competent digital receiver is supposed to resolve any likely data timing issues that arise. If certain obsolete products didn't do this, that must be one reason why improved models were produced.

Again Amir you seem to have no up-to-date technical measurements of the HDMI performance of AVRs that are currerntly on the market as new products.
So I thought he may be right. There is a newer generation of HDMI transceivers and subsystems every couple of years so I should test and report back. I had no expectations of how they all would perform. I gathered all the devices that I had and could borrow from work and made my measurements. As you have seen, there is no improvement at all since Paul Miller did his measurements in 2008/2009. It is the opposite of the say that squeaky wheel gets the oil. In this case there has not been enough of a "squeak" as to get mass market vendors to deal with this issue properly.
You simultaneously praise a member for his modesty and post a self aggrandizing account of your battle scars and your rise to fame via a "forum down" random quote. I don't know what to do with this. Is this where everything as we know it simultaneously explodes at the speed of light ?
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