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Old 4th July 2018, 11:06 AM   #21
Pygmy is offline Pygmy  Netherlands
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I'm wondering - is anyone seeing differences in TV image between different (but good working) HDMI cables?
 
Old 4th July 2018, 11:51 AM   #22
Samsara is offline Samsara  France
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Quote:
Originally Posted by Pygmy View Post
I'm wondering - is anyone seeing differences in TV image between different (but good working) HDMI cables?
It's very easy to demonstrate. Just take photos (16MP or more, 4K is 8MP) or use a 4K 120Hz camera.
But no manufacturers or resellers of HDMI cables provides this evidence, no one ...
 
Old 4th July 2018, 12:05 PM   #23
rmaudio is offline rmaudio  United Kingdom
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Originally Posted by JPS64 View Post
Iīm using USB for military custom development.
Iīve used COTS cable at the beginning with very bad results although cable marking High Speed USB (cheap or expensive ones, donīt 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 donīt 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
Yes - lots of 'commercial' USB cable products can be less than optimal - but ime this is usually in terms of interference (both ways) and typically the USB link will break down or be 'lost'. If your audio screeches or glitches or just stops then - yes - the cable might be the issue.
But it isn't likely to result in (making up audiophile speak - "a constricted upper midrange on solo female vocals").
Eye Diagrams / ESD and Common Mode filtering - yes - now talking proper engineering !

The real question wrt Audio transmission would seem to be the degree to which the 'playback' clock is separate from the 'USB clock'.

for info I use USB comms in Industrial / Scientific Test Instrumentation.
 
Old 4th July 2018, 12:08 PM   #24
Johnny2Bad is offline Johnny2Bad  Canada
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The idea that there is some kind of digital signal being transferred by any cable is just as erronius as the idea that the manipulation of digital data in a CPU (made of transistors, resistors, capacitors, pathways) or a memory chip is a digital signal. It's digital *data* but the electronic signals are AC analog, they only *represent* digital data.

So, regardless of your position, or your experience, with regard to digital transmission via cable, you must acknowledge that a simple 16/44 file via USB is a square wave at almost 45 KHz. Square waves can also be mathematically described as a series of sine waves whose harmonics are at ever higher frequencies to the fundamental overlaid on top of each other with integrity in the time domain. So this is not your 20Khz analog cable, or even your 45KHz analog cable.

Higher resolutions mean higher frequency AC signals, and in every case they must be properly transmitted and "understood" by the receiving system which will process each and every bit via an analog circuit.

With sufficient resolution (using a GHz scope) errors in USB cables are easily discerned. Two examples reproduced below: highlighted areas indicate where a change from a digital one or zero to the opposite polarity fails to make it sufficiently across the zero-crossing point to be identified as such by any downstream device. The images are a measure of a USB cable from a Digital Frequency Generator to the Scope at 16/44 resolution.
Attached Images
File Type: jpg Digital Data Errors1.jpg (105.7 KB, 192 views)
File Type: jpg Digital Data Errors2.jpg (112.0 KB, 191 views)
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Last edited by Johnny2Bad; 4th July 2018 at 12:18 PM.
 
Old 4th July 2018, 12:20 PM   #25
rmaudio is offline rmaudio  United Kingdom
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Originally Posted by Johnny2Bad View Post
The idea that there is some kind of digital signal being transferred by any cable is just as erronius as the idea that the manipulation of digital data in a CPU (made of transistors, resistors, capacitors, pathways) or a memory chip is a digital signal. It's digital *data* but the electronic signals are AC analog, they only *represent* digital data.

So, regardless of your position, or your experience, with regard to digital transmission via cable, you must acknowledge that a simple 16/44 file via USB is a square wave at almost 45 KHz. Square waves can also be mathematically described as a series of sine waves whose harmonics are at ever higher frequencies to the fundamental overlaid on top of each other with integrity in the time domain. So this is not your 20Khz analog cable, or even your 45KHz analog cable.

Higher resolutions mean higher frequency AC signals, and in every case they must be properly transmitted and "understood" by the receiving system which will process each and every bit via an analog circuit.

With sufficient resolution (using a GHz scope) errors in USB cables are easily discerned. Two examples reproduced below: highlighted areas indicate where a change from a digital one or zero to the opposite polarity fails to make it sufficiently across the zero-crossing point to be identified as such by any downstream device. The images are a measure of a USB cable from a Digital Frequency Generator to the Scope at 16/44 resolution.
Fine. So you'll have errors in the data and your USB link will likely fail - depending on where the errors occur in the USB data stream - or at least your audio will sound clearly wrong.
This only really happens due to interference or USB cables that are too long.
Also, isn't the data rate going to be a lot higher than the 45kHz figure stated - assuming a 'Stereo' signal transmitted - each of L/R running at 44.1kHz with 16 bits encoded plus all the other stuff that goes on the USB protocol. Gets you into MHz figures.
 
Old 4th July 2018, 12:21 PM   #26
lcsaszar is offline lcsaszar  Hungary
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Originally Posted by 00940 View Post
I think you're confusing adaptive and asynchronous protocols. What you describe is true for adaptive endpoints (the pcm2*** serie from TI for example). Definitely not for the more modern interfaces like xmos, which work as asynchronous endpoints.

There are 3 modes for audio transfer under USB audio. All 3 are falling in the isochronous category (real time with no error correction).

From the USB Device Class Definition for Audio Devices:



For more details on the synchronization methods, see section "5.10.4.1
Synchronization Type" from the Universal Serial Bus Specification Revision 1.1.
Thanks for the explanation. I made out of it that asynchronous transfer is best for audio. That makes the DAC independent from the host with regard to clocking. But in this case there shouldn't be any influence of cables on the clock purity, right? Those who claim can hear any difference in USB cables must have used synchronous transfer, correct?

Here I found some useful information
 
Old 4th July 2018, 12:23 PM   #27
Pano is offline Pano  United States
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Since it is trivially easy to send billions of bits across USB cables without the loss or error of even one bit, not one part in a billion - the only arguments left are jitter and noise. Bit perfect is easy.

Jitter and noise are not difficult to measure in the analog output signal from the DAC. You can see them in an FFT analysis. If they aren't getting thru the DAC, it doesn't matter. Well, it doesn't matter for those of us who listen to the resulting analog signal. For those of you who listen directly to the USB bitstream, then it could make a difference.

If you can see noise and jitter in the FFT, fix it. We do have the tools to figure this out, right?
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Old 4th July 2018, 12:24 PM   #28
Johnny2Bad is offline Johnny2Bad  Canada
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I'm not suggesting that a USB cable need be "exotic" or even expensive, but it certainly has to be competent, and the idea that one that "seems to work" must therefore be error free is suspect. And if there are errors, then there could be audible differences.
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Old 4th July 2018, 12:26 PM   #29
Johnny2Bad is offline Johnny2Bad  Canada
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Originally Posted by rmaudio View Post
Fine. So you'll have errors in the data and your USB link will likely fail - depending on where the errors occur in the USB data stream - or at least your audio will sound clearly wrong.
This only really happens due to interference or USB cables that are too long.
Also, isn't the data rate going to be a lot higher than the 45kHz figure stated - assuming a 'Stereo' signal transmitted - each of L/R running at 44.1kHz with 16 bits encoded plus all the other stuff that goes on the USB protocol. Gets you into MHz figures.
Well, I'd have to do some searching for the original video where the screen grabs came from (a test of the 'scope) but the cable looked to be about a half meter.

People who buy cable in good faith and hear sonic differences between two examples of different construction and materials should not have to own and use a test suite to verify exactly what issue is behind it, or be belittled because their results are "impossible".

None of that requires the purchase of "exotic" cable either; consumers should expect competent performance from whatever they choose to purchase. I don't see it as surprising that a cable of a different price point might be better constructed or more suitable for the purpose it's described to meet either.
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Last edited by Johnny2Bad; 4th July 2018 at 12:37 PM.
 
Old 4th July 2018, 12:27 PM   #30
Pano is offline Pano  United States
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You can easily check it for errors. Same with SPDIF. If you find errors, then you have a very bad cable.
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