Let’s talk why USB cable makes a difference

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DPH

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I don't doubt he's a good guy and has entirely honest intentions! No strike against the guy, just against the test.

Methodologies to actually test the efficacy of a USB cable are, well, something that can be clearly defined within a factual realm (doing EE stuff to discern, whether or not you're a degreed EE, I don't care) without needing to go to inordinate lengths of floury, ultimately useless language.

Is there a difference in the performance of the device attached to the USB cable? Yes? No? How big of a change? That's a very relevant test which will elucidate the effects of cables on *that* system, regardless of whether such differences are ultimately audible. And something that others can learn from.
 
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DPH

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JPS64 said:
I´m using USB for military custom development.
I´ve used COTS cable at the beginning with very bad results although cable marking High Speed USB (cheap or expensive ones, don´t care).

After a lot of expertising with a lot of measurements (LeCroy with fixture according USB standard, eye diagram...) we state that this is like russian roulette.
So we decide to use only custom made and qualified cable from Draka.
We don´t need any ferrite on cable, but the interface is ESD protected and CMC EMI filtered on PCB.
This is a technical issue.

My 2 cents.
JP
Click to expand...

I know you mentioned you hope to share some later, but I look forward to what you have. Any reason why you guys picked USB for anything mission critical like this over other communication hardware/protocols? Sounds like you're asking for above and beyond the spec, which would also make sense why you need the filtering.
 
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andy2

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Joined 2004
00940 said:
This "shoot out" by hifi news has some eye pattern. Not a lot of differences between the cable: http://mvicha.sweb.cz/test USB kabelu.pdf

Iirc, they ran a more technical serie of tests in the January 2011 edition. From memory, the computer had much more influence on jitter results than the cables.
Click to expand...

So how much for one night with Crystal Cable Absolute Dream?

By the way, the "Eye" diagram they measured for rise time is just too simple minded. It's like judging the car using 0-60 times.
 
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JPS64

JPS64

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Joined 2011
@DPH


We don´t use USB for mission critical equipment then we´re developping information systems. But we like to use serial to USB converter also for radio. I can say that we´ve no problem since today.


DO or equivalent AIRBUS EMI requirements and hardware qualification shows us that we need some filtering on the USB interface.


JP
 
Pano

Pano

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andy2 said:
I should add one more category to my original list
1. Power rail
2. Ground
3. Jitter induced noise : that is usb jitter of the incoming data induces noise.
4. Data rise time.
5. Common mode current.
Click to expand...
None of these matter if they don't show up in the analog audio output. It's not difficult to test for these in the analog signal, even far below audibility. If the digital signal path rejects these (and its designed to do so) they won't show up in the analog output. And if they aren't there, why do they matter?
 
Pano

Pano

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It's been done several times right here on this forum. I did some of the tests, SY did too. I think there are others.
Yes, you can find bad cables and bad interfaces, but they measure poorly. Anything not pathologically bad shows noise and jitter sidebands so low you'd never hear them.
 
gpapag

gpapag

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JPS64 said:
@DPH
We don´t use USB for mission critical equipment then we´re developping information systems. But we like to use serial to USB converter also for radio. I can say that we´ve no problem since today.

DO or equivalent AIRBUS EMI requirements and hardware qualification shows us that we need some filtering on the USB interface.
Click to expand...

Reference please. I wouldn’t like to see this turn into the fancy and catchy scenario “amplifier chassis milled out of an airspace grade aluminum alloy billet” without your consent.

http://www.icas.org/media/pdf/Workshops/2015/ICAS_Workshop_Roemelt.pdf
https://www.testforce.com/testforce...dicalSeminar2016/SpirentMedicalDO-160GMIL.pdf
https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_21-16G.pdf

George
 
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