Kudos to Amir

Ethan Winer

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I don't know how many WBF'ers read Widescreen Review magazine, but Amir has been writing a regular column about various audio topics. This month's (March 2013) article about jitter is the best yet. He explains the different types of jitter and their causes, and shows lots of graph to supplement the text. Hopefully Amir will put this article on his own web site after a suitable period, and link to it from here so everyone can see it.

As some of you may know, Amir and I had an extended discussion about jitter a while back, with me arguing that while jitter is real I don't think it's actually an audible problem. Son of a gun, Amir came to the same conclusion in this article, and he even explained why it's not necessarily audible (masking of nearby frequencies). However, I agree that audio designers need to aim higher than "borderline acceptable" for several reasons. For example, audio typically passes through many devices in a row, so if each is just barely transparent the sum of artifacts can be audible.

Anyway, I just wanted to compliment Amir for his good work, and I learned several things myself.

--Ethan
 

ack

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On another day but today, I would believe it
 

Gregadd

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sum of artifacts can be audible.

it's even worse is the artifacts are complimenary.:b
 

Roger Dressler

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However, I agree that audio designers need to aim higher than "borderline acceptable" for several reasons. For example, audio typically passes through many devices in a row, so if each is just barely transparent the sum of artifacts can be audible.
As long as those cascaded devices are all analog or all digital, there will be no accumulation of jitter. It just underscores the good practice of minimizing the number of digital/analog conversions in the signal path.
 

amirm

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Thanks Ethan. :) It was Amir pretending to be an equipment reviewer for a change :) :). It was a lot of work to assemble all that gear but also fun and revealing. Now that the article is in print, I will work on an online version and post here when done. What's neat is that I have 10X more data than what I could fit in the article.

Here is a picture of the gear which I had post here before:

 

amirm

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Sure. The AV gear is such: (cutting and pasting from the article with the commentary)

"1. Mark Levinson No 360S. I have had this since 1999 and it is my reference DAC for critical listening tests at my workstation. It is quite an antique relative to flashy newer devices. So in theory, folks should have had no problem outperforming it. Needless to say, this DAC does not have HDMI so testing was limited to its S/PDIF port only.

2. Lexicon 12B processor. This is my beloved processor which has been collecting dust since it does not have HDMI. I think the 12B was introduced around 2003. Again, it will be interesting to see if the new kids on the block outperform it.

3. Onkyo TX-SR805 and Yamaha RX-V861 are a couple of AVRs I have on hand for bench testing. They are about four or five years old as of this writing. Retail prices at the time were in the $1,000 range from what recall.

4. Pioneer Elite SC-63 and Anthem MRX-300 are newer AVRs introduced in 2012, and 2011 respectively. They represent premium offerings in AVRs in today’s market.

5. Anthem AVM-50 is an example of semi-high end processors retailing at $5,500. One would expect it to outperform other AVRs and the company’s own integrated product, MRX-300.

6. Mark Levinson 502. This was the mother of all processors when announced back in 2008 at a retail price of $30,000. Unlike older high-end processors, this one actually has HDMI on it. Sporting 18-layer (!) PC boards, this design is more complicated than half a dozen computers put together. It takes an hour just to disassemble it. I know, I have done it! Unlike many other HDMI implementations, this one has a custom designed subsystem (others buy modules since they don’t have in-house expertise or volumes to design their own). The unit is still in production today at lower prices. I had no expectations about its performance going into the testing but came out extremely impressed as you will see later.

7. Tact RCS 2.0. This is a 2-channel processor with quite a cult following from a small company known for its “room correction” (EQ). A colleague had it in his storage and when he heard I was doing this testing, he offered it for use. It of course does not have HDMI so its testing was limited to S/PDIF.

8. Peachtree decco65. This is an integrated DAC and power amp. Cute little device. Question is, does it do better than mass market AVRs? Again, no HDMI but good reference regardless."


The test gear on the left are my Audio Precision Analyzer (hidden mostly behind the laptop screen), a "monster power conditioner" I use as a fancy power strip with a useful volt and amp meter, Tektronix oscilloscope and in the middle next to the audio stack is the Prism Sound dScope that was used to perform all the measurements (was much easier to set up and use than my Audio Precision).

The Berkeley Alpha USB to S/PDIF converter is sitting on top of the Prism Sound dScope and the Audiophilleo is hidden behind one of the boxes.
 

amirm

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Just to add some context, the idea behind the article came from an argument on another forum where some claim that the high jitter issue on HDMI may have gone away with advances in ICs/products. Since Paul Miller who was the only reviewer who had ever bothered to measure HDMI jitter has stopped testing such products for a couple of years now, there was a vacuum of data with respect to how HDMI and S/PDIF compare in today's products. For that reason, you see the AVRs/Processors being tested. But since I had a few other non-HDMI devices, the article at the end covered S/PDIF performance, including comparing three USB implementations (Berkeley, Audiophilleo and Decco).

I had only a day to write the article so per earlier note, I did not put a lot of the measurements there.
 

Ethan Winer

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As long as those cascaded devices are all analog or all digital, there will be no accumulation of jitter. It just underscores the good practice of minimizing the number of digital/analog conversions in the signal path.

Right, that's why I used the word "artifacts" because I was speaking more generally. These days most audio devices are sufficiently transparent to not degrade the sound audibly. But there are many devices in the path between a studio microphone and the end listener's loudspeakers. So it's good practice to aim for, say, 20 dB better than is audible at each device. Likewise for response changes. If each of ten devices in series is flat within 0.1 dB, then you'll be within 1.0 dB at the far end.

--Ethan
 

jkeny

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Feb 9, 2012
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Yes. Amir congrats on your continued series of informative articles on WSR & thanks to Ethan for drawing our attention to it.
However, I'm surprised that you didn't correct Ethan's incorrect paraphrasing of your article

The quote from your article reads: " When the distortions are close to a loud signal, and our source certainly is one in this case, they can’t be heard. So mostly like these are not audible distortions. As we get farther from the main tones, the spikes can reach higher than level of audibility and the chance of this occurring with HDMI is higher than with S/PDIF."

Ethan's paraphrasing
...
As some of you may know, Amir and I had an extended discussion about jitter a while back, with me arguing that while jitter is real I don't think it's actually an audible problem. Son of a gun, Amir came to the same conclusion in this article, and he even explained why it's not necessarily audible (masking of nearby frequencies).
--Ethan

He also seems to miss your recommendations "My advice is that if you are using your system for critical music listening, use S/PDIF instead of HDMI. If you are using a PC or Mac as the source, invest in a high- quality USB to S/PDIF converter. "

He also fails to recognise that you restricted to "Two cases of it are simple to analyze though:" Sinusoidal & Random jitter. Any thoughts on data correlated jitter & it's possible distortion products?

One of the most interesting graphs in the article is the one showing just how ineffective the SPDIF PLL implementations are, with most giving none or -10dB reduction in jitter & only the two Levinson devices doing any better.

Again, well done but don't let your excellent article be paraphrased into a simplistic & incorrect paraphrasing of your statements
 

jkeny

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Feb 9, 2012
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The other graph that I found intriguing & interesting was the ultrasonic range measurements. This seems odd - the o/p filter is letting through this level of OOB images?
BTW, are these FFTs? If so is the noise floor not a direct reading from the grass of the FFT graph but rather a calculation based on bin size used?
 

amirm

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Yes, those are FFT noise floor. I had revised the article to get that statement in there but not sure if it made it into the article.
 

ack

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Yes. Amir congrats on your continued series of informative articles on WSR & thanks to Ethan for drawing our attention to it.
However, I'm surprised that you didn't correct Ethan's incorrect paraphrasing of your article

The quote from your article reads: " When the distortions are close to a loud signal, and our source certainly is one in this case, they can’t be heard. So mostly like these are not audible distortions. As we get farther from the main tones, the spikes can reach higher than level of audibility and the chance of this occurring with HDMI is higher than with S/PDIF."

Ethan's paraphrasing


He also seems to miss your recommendations "My advice is that if you are using your system for critical music listening, use S/PDIF instead of HDMI. If you are using a PC or Mac as the source, invest in a high- quality USB to S/PDIF converter. "

He also fails to recognise that you restricted to "Two cases of it are simple to analyze though:" Sinusoidal & Random jitter. Any thoughts on data correlated jitter & it's possible distortion products?

One of the most interesting graphs in the article is the one showing just how ineffective the SPDIF PLL implementations are, with most giving none or -10dB reduction in jitter & only the two Levinson devices doing any better.

Again, well done but don't let your excellent article be paraphrased into a simplistic & incorrect paraphrasing of your statements

Thanks for posting this. I was certain Amir, like any competent technical person, would never claim jitter is inaudible.
 

DonH50

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Jun 22, 2010
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^ Seems a bit harsh. I know plenty of very competent technical folk who would say a number of commonly-cited artifacts are inaudible at the levels of most modern electronics. And very few who would ever use the word "never". :)

Ethan, thanks for pointing this out, and thank you Amir for the article. I look forward to reading it, soon as I have more time (or spend less perusing forums like this!)
 

NorthStar

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-- Anyone here knows what is the average thickness of the wire inside a digital coaxial cable?

...And the thickness of a single wire (from nineteen of them) inside a digital HDMI cable?

* Digital Optical; the sound is too loose, too detached, lacking firmness. IMO
 

NorthStar

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Look up coaxial and HDMI cables.

Generally 22 to 26 AWG, seen as small as 28 AWG.

Don't think there are analog HDMI cables... :)

Don, the questions were an invitation to see if the very tiny wires inside a digital HDMI cable could have an effect on sound quality via audio signals transfer. ...As compared to a digital coaxial one which is much thicker, more solid, more durable.
And! ...If there is any correlation with jitter?

* No, there isn't any analog digital HDMI cable. ;)
 

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