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Eye pattern, what does it tell us

tuga

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Hi-Fi News tested a bunch of USB cables and published catchy eye pattern measurements for each one of them (along with some subjective blabber).
Those eye pattern plots show some differences between the different cables.

How does one read an eye pattern plot?

What does it tell us about the effectiveness of a USB cable?
 

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Soniclife

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Sounds like pure FUD, for async usb the clock is not coming from the cable, like it can be with other digital comms. So if the cable is good enough to pass the data correctly all should be well.
 
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tuga

tuga

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Sounds like pure FUD, for async usb the clock is not coming from the cable, like it can be with other digital comms. So if the cable is good enough to pass the data correctly all should be well.
It's what comes out of the DAC that matters, not how things look at some intermediate step, especially in the digital domain.
You haven't answered any of my questions.
 

EdW

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A simple tutorial on eye diagrams:
https://www.edn.com/eye-diagram-basics-reading-and-applying-eye-diagrams/
These cables all have reasonably or very solid eyes and the data transmission should be perfect with a good USB receiver. It is impossible for eye diagrams like these to result in detectable errors with a Bit Error Rate Test (BERT).
Paul Miller truly has golden ear ears if he can distinguish between these cables in a double blind audio test!
 

Soniclife

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You haven't answered any of my questions.
I answered your last question, which is the only one that really matters. You can study eye patterns elsewhere on the web easily enough if you are really interested. The rest of it is just an attempt to build a strawman argument for cables mattering.
 

Doodski

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Hi-Fi News tested a bunch of USB cables and published catchy eye pattern measurements for each one of them (along with some subjective blabber).
Those eye pattern plots show some differences between the different cables.

How does one read an eye pattern plot?

What does it tell us about the effectiveness of a USB cable?
I start with looking at the possible indecisiveness of the pattern waveform. All those eye patterns look very symmetrical and would pass as a zero or a one in digital transmission. That's what matters in this case.
 

Purité Audio

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How hugely disappointing, the BS never ends does it, Miller developed a measuring suite which I believe is still extensively used, I guess money makes you do things ...


Keith
 

kschmit2

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also Rohde & Schwarz on USB:

page 22: https://cdn.rohde-schwarz.com/pws/d...ion_notes/1ma188/1MA188_1e_USB2_MaskTests.pdf

testing explained a bit: https://de.slideshare.net/RohdeSchwarzNA/usb-20-compliance-testing

and more can be found here: https://www.rohde-schwarz.com/us/search/search_63238.html?term=eye+diagram

It doesn't tell you anything about whether a better looking eye diagram corresponds with audible differences.
The primary reason is compliance testing against a given standard.

They do have decent video explanations though:
https://www.rohde-schwarz.com/us/kn...roduction-video-detailpage_251220-654464.html
https://www.rohde-schwarz.com/us/kn...surements-video-detailpage_251220-654528.html
 

kschmit2

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and here's a bonus if you really want to learn more about eye diagrams:

Register for the upcoming webinar on 2 March 2021:
Electronic design webinars - Oscilloscope series
5 steps to a realtime eye diagram - signal integrity debugging
This webinar is intended for engineers who work on the design and testing of high-speed interfaces. We will start with typical design challenges and methods in order to approach the signal integrity analysis. Eye measurements will be the focus of this webinar. After a quick introduction to the basics, we will explore the five steps needed to get to a realtime eye diagram. With practical examples and demonstrations, we will illustrate the signal preparation, clock data recovery, mask test and histogram, serial pattern trigger and cable loss deembedding.

Registration link: https://www.rohde-schwarz.com/us/kn...realtime-eye-diagram-registration_254311.html
 

Soniclife

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How hugely disappointing, the BS never ends does it, Miller developed a measuring suite which I believe is still extensively used, I guess money makes you do things ...


Keith
He has a magazine to sell, which needs advertisers, very disappointing as he surely knows exactly what he is doing.
 

DonH56

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I use eye diagrams at work all the time. Perhaps the most relevant for audio interfaces would be any large amplitude dips in the middle (closing the eye) or any sparkles (dots) in the middle indicating potential bit errors.

Think of a digital bit stream comprised of random 1's and 0's as the high and low parts of the waveform. Now take the stream and fold all of the bits on top of each other to form an eye. The edges are where the bit stream transitions from 1 to 0 and vice-versa. You want the middle part of the eye to be "open" and edges to be sharp instead of broad and fuzzy due to jitter.

HTH - Don
 

Doodski

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I use eye diagrams at work all the time. Perhaps the most relevant for audio interfaces would be any large amplitude dips in the middle (closing the eye) or any sparkles (dots) in the middle indicating potential bit errors.

Think of a digital bit stream comprised of random 1's and 0's as the high and low parts of the waveform. Now take the stream and fold all of the bits on top of each other to form an eye. The edges are where the bit stream transitions from 1 to 0 and vice-versa. You want the middle part of the eye to be "open" and edges to be sharp instead of broad and fuzzy due to jitter.

HTH - Don
I'm used to a RF eye pattern from a laser assembly pickup or a helical scan assembly. The jitter and sparkle is apparently seen. Adjustment includes sharpening the edges and making the eye as visible as possible. We used to use the 3rd to 5th eye over from the left voltage trigger of the analogue scope. Minimum 100 Mhz and preferably a Tektronix 7000 series lab scope. No idea what you are using @DonH56 but I imagine it's pretty kewL.
 

solderdude

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The eyepattern receiver (amongst it its's impedance) and its hysteresis as well as de-jitter circuit behind it (and subsequent clock retrieval) determines how much degradation is allowed.

Indeed, as has been mentioned before. It is all about the middle part. Large 'ringing' that makes it to the trigger point (the middle part of the eye pattern) can cause problems.
The middle part (and slightly above and below) is where it gets 'decided' if the signal is low or high. These aren't the actual audio containing bits though. In case of USB these are changes from H to L and L to H. This is decoded, along with the recovered clock, and the package including checks, redundancy and other digital info (including the audio bits) are then extracted and stored for a short period.
There is a certain 'range' where the zero crossings can fall to be reliably detected. Therein lies part of the robustness of the connection. A 'cleaner' signal isn't necessarily containing better data, or higher quality sound.
 

DonH56

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I'm used to a RF eye pattern from a laser assembly pickup or a helical scan assembly. The jitter and sparkle is apparently seen. Adjustment includes sharpening the edges and making the eye as visible as possible. We used to use the 3rd to 5th eye over from the left voltage trigger of the analogue scope. Minimum 100 Mhz and preferably a Tektronix 7000 series lab scope. No idea what you are using @DonH56 but I imagine it's pretty kewL.

I do mainly receive testing for SAS/PCIe interfaces so the eyes are generated by built-in HW (inside the chips). For calibration and Tx testing typically 33 GHz to 63 GHz DSOs from Tek or Keysight at 100 GS/s, the usual suspects.
 

Doodski

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For calibration and Tx testing typically 33 GHz to 63 GHz DSOs from Tek or Keysight at 100 GS/s
Rolling eyes... Oh that sort of bandwidth. :D One must be a expert in metrology to even approach such a measurement. That's harder-core measuring.
 
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tuga

tuga

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I answered your last question, which is the only one that really matters. You can study eye patterns elsewhere on the web easily enough if you are really interested. The rest of it is just an attempt to build a strawman argument for cables mattering.
So point me to one of those sources instead of being sarcastic. I’m using a Lindy USB cable by the way, not trying to build anything made of straw... :rolleyes:
 

cursive

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So point me to one of those sources instead of being sarcastic. I’m using a Lindy USB cable by the way, not trying to build anything made of straw... :rolleyes:


This video really helped me understand eye patterns better. But ultimately keep in mind what Solderdude said with respects to USB specifically.
Therein lies part of the robustness of the connection. A 'cleaner' signal isn't necessarily containing better data, or higher quality sound.
 

Soniclife

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So point me to one of those sources instead of being sarcastic. I’m using a Lindy USB cable by the way, not trying to build anything made of straw... :rolleyes:
The post just before that one you quoted didn't help you? Or any of the subsequent posts with links in them?
A Lindy cable will work just fine, until it breaks, which will be obvious.
 
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