About USB cables in general

[Brillo]

There is a lot of knowledge surfacing on the 'bits are bits' thinking now. I suggest you also read a little bit of that. Then you can return with an extended knowledge on how it all works.

That’s good to know. Please can you supply links to these knowledge sources?

I ask because my general view sides with the OP. I have always been a sceptic but recently bought a reasonable quality USB cable and I was convinced it improved the sound. My ITC friend rubbished my perception. I’m now in a quandary as to whether that was an ‘expectation bias’ experience or whether it really did make a difference.

Like, I expect, every other streaming listener, I just want to create the best sound to listen to, so look forward to your reply. No axe to grind here. I just want straight facts and information.

One thing I like about being an engineer is learning about new and interesting topics, and having my firmly held ideas challenged by new research. I usually squirm a bit when I hear/read something like what Greg posted: knowledge sources, straight facts and information are at your fingertips, and asking others for them sounds like a case for lmgtfy.com! It is just as easy to search for information about the USB protocol, physical layer and testing tools as it is to search for audiophile quality high end USB cables (wired in the right direction, of course). This being said, there are some cases that are a bit more nuanced... I feel this is one of them.

When confronted with an engineering problem, I like to keep in mind that the way you ask the question can influence the outcome, as can the scope of the answer (a nice example here). In this case, you could limit the answer to "is bits are bits a valid argument", i.e. can a USB cable's intrinsic "quality" influence the values of PCM samples coming out of a USB audio receiver device? You could also go a step further and add time information – can the cable influence the USB interface timing? But then you have to ask, does the jitter on an asynchronous USB link get passed through to the synchronous PCM output?.

The first part – is it true that bits are bits –  is not too hard to answer. This can effectively be described as stated, i.e. packaged "fancy" water being transported by a vehicle, but there is an additional variable, the USB packet CRC code. This can be painted in the ongoing narrative as a shock indicator and safety seal. How do you know not to trust a bottle that's been handled roughly? If the shock indicator on the packaging (the CRC of the USB packet) is red or if the safety seal is broken, you can safely assume that the package has been handled roughly and should not be accepted. If this is the case, the receiving party does not sign for the package (does not ACK in the USB protocol) and the package must be sent again. This goes on until the package arrives in good condition. Will deliveries made by a Mercedes be refused less frequently than those made by a Fiat? Probably not... As long as the cable meets the specified differential impedance or 90Ω, maximum propagation delay of 27ns, and maximum propagation skew of 100ps between the differential lines (such as this one), everything should be more than fine, and the USB driver and receiver electronics are probably mush more prone to behaving badly. Also, the CRC error rate is easily measured by any USB protocol analyzer (see here), so there is very little room for interpretation. Plug a cable into an analyzer setup and see if is induces errors. And so what exactly does happen if packages start getting refused? The bitrate is reduced since time has to be spent resending packets. Is this reduction audible? If things get bad enough, the USB link will be closed since the protocol has faulty device detection built in, or drops will occur and yes, that is definitely audible. Other than that, the bits will come out exactly as they went in.

So what about timing? This is quick: the answer is no. First, all dedicated USB audio chips I've used (such as this or this) have dedicated external media clocks. For software based systems, the media clock is generated by the CPU core clock (more exactly the system's wall clock). The USB clock is not recovered as it would be in an AES-3 link (S/PDIF, etc.). Second, jitter introduced by a (passive) cable is deterministic and will not affect anything if within the tolerances of the USB spec, which are quite generous.

So that's it? Well, if it were that simple, I'm not sure there would be so many "high end" cable manufacturers around... You could also extend the investigation to parasitic analog effects. Can the USB cable inject RF or EMI noise into a system? If so, what level of noise on the output would constitute an audible effect? 3dB below the system's self noise? 100dB below? And how do you decide on what level of RF and EMI noise to subject your setup to? What is the noise profile? Narrow band? Wide band? What frequencies are audible? If you superimpose 2.4 GHz on your audio ground, does it introduce something you can hear in the acoustic signal coming from the speakers? Then you can start asking even more questions – If the USB cable has a poor shield, the differential data pair and the receiver chip's CMRR will have to be slightly better, but won't less noise be coupled through to ground? It depends. Is the source device dumping junk through the shield to the downstream device? It depends. Will the inherent "quality" of the cable alter the way all of these things interact? It depends. And since "it depends", there's room for magic (read "marketing"). 

So does the quality of the cable's shield make a difference? The answer is more complicated, but probably "no". The way grounding affects noise in a system is almost entirely dependent on the design of the receiver's electronics, not the cable attached to them. Of course, a defective or just plain "bad" cable (e.g. not correctly shielded, extremely long, impedance way out of spec...) can cause strange things to happen, but in order to not stray too far we will assume here that that is not the case. (Using our delivery vehicle analogy, just avoid square wheels on the delivery truck, or trying to deliver a shipping container with a bicycle.)


Oh well, I had nothing else to do on a Sunday afternoon...

[Stino]

USB cables are always a debate (as other digital cables).

Like many other protocols hand-shaking is in place. In addition, many of the new streamers have quite a large buffer. So a decent cable or a real high-end cable should not bring any concern on whether the package is received correct and on time.

So in case you are transporting data that is already in digital form (like a streamer with big buffer) to a DAC (like a Devialet with sufficient buffer) - meaning to take out the timing effects of converting analogue to digital first - then I do not get why cables would differ.

But I'm sure I'm wrong some how...

Anyways, I enjoy reading people's observations even though - just like mine - they are probably highly biased indeed.

[Greg]

That’s good to know. Please can you supply links to these knowledge sources?

I ask because my general view sides with the OP. I have always been a sceptic but recently bought a reasonable quality USB cable and I was convinced it improved the sound. My ITC friend rubbished my perception. I’m now in a quandary as to whether that was an ‘expectation bias’ experience or whether it really did make a difference.

Like, I expect, every other streaming listener, I just want to create the best sound to listen to, so look forward to your reply. No axe to grind here. I just want straight facts and information.

One thing I like about being an engineer is learning about new and interesting topics, and having my firmly held ideas challenged by new research. I usually squirm a bit when I hear/read something like what Greg posted: knowledge sources, straight facts and information are at your fingertips, and asking others for them sounds like a case for lmgtfy.com! It is just as easy to search for information about the USB protocol, physical layer and testing tools as it is to search for audiophile quality high end USB cables (wired in the right direction, of course). This being said, there are some cases that are a bit more nuanced... I feel this is one of them.


Oh well, I had nothing else to do on a Sunday afternoon...

Thank you for your condescending reply. I am sorry you had to waste your Sunday afternoon in order to patronise me in your second post on this forum.

My understanding of forums that work well are that they are communities of people with a variety of life skills, knowledge and abilities and the members are happy to share their knowledge for the benefit of all.

I have carried out www searches as you have suggested but invariably can never come to any conclusion, mainly because I don’t understand what I read. I have no doubt that the majority of audio enthusiasts have the same experience. By way of example, I don’t understand the bulk of what you wrote in your reply. This is another of the reasons why marketing can grip the industry, and we all know marketing represents the opposite of honesty.

People like me will always be dependent on the knowledge of others who know the science. We also want those who know to share their conclusions. I and others have to depend on trusting what others who seem to know (such as yourself) say. Of course, our own ears will always be the final arbiter, but it is good to have a path to follow before making that arbitrary conclusion as it should save us a pile of money in the meantime. The bottom line for those of us who do not understand the intricate science is, we need to have trust and belief in our advisors and only independent versions will do, of which I know there are many out there.

As you have joined here, I hope you want to contribute constructively for the benefit of the community. Are you independent? Are you connected to the Hi-Fi industry? Can you see the dilemma so many of us are in? As ever, it’s the ears that have it, but with the help of people like you, if impartial, those of us dependant on our ears in this way could find a relative easy and probably much more affordable passage in the pursuit of our hobby.

What do you think?

[K4680]

There is a lot of knowledge surfacing on the 'bits are bits' thinking now. I suggest you also read a little bit of that. Then you can return with an extended knowledge on how it all works.

That’s good to know. Please can you supply links to these knowledge sources?

I ask because my general view sides with the OP. I have always been a sceptic but recently bought a reasonable quality USB cable and I was convinced it improved the sound. My ITC friend rubbished my perception. I’m now in a quandary as to whether that was an ‘expectation bias’ experience or whether it really did make a difference.

Like, I expect, every other streaming listener, I just want to create the best sound to listen to, so look forward to your reply. No axe to grind here. I just want straight facts and information.

The only way for you to determine for sure if this is expectation bias or outside of your brain would be to go through a often considered tedious ABX test between the two cables. 

This being said, and for full disclosure I’m leaning more on the bits are bits side of the fence and cables are cable, if you perceive the overall result at being better and if you can afford it, why not just enjoying it?

Here is the trick in my mind, although there is an objective and measurable part of the path of the music (basically between the source and our ears or brain) the last few inches (within our brain) is where a lot of the magic occurs. 

Jean-Marie

The listening experience is a very personal sensory impression and not a technical measure! Enjoying music is subjective and emotional.

[Greg]

That’s good to know. Please can you supply links to these knowledge sources?

I ask because my general view sides with the OP. I have always been a sceptic but recently bought a reasonable quality USB cable and I was convinced it improved the sound. My ITC friend rubbished my perception. I’m now in a quandary as to whether that was an ‘expectation bias’ experience or whether it really did make a difference.

Like, I expect, every other streaming listener, I just want to create the best sound to listen to, so look forward to your reply. No axe to grind here. I just want straight facts and information.

The only way for you to determine for sure if this is expectation bias or outside of your brain would be to go through a often considered tedious ABX test between the two cables. 

This being said, and for full disclosure I’m leaning more on the bits are bits side of the fence and cables are cable, if you perceive the overall result at being better and if you can afford it, why not just enjoying it?

Here is the trick in my mind, although there is an objective and measurable part of the path of the music (basically between the source and our ears or brain) the last few inches (within our brain) is where a lot of the magic occurs. 

Jean-Marie

The listening experience is a very personal sensory impression and not a technical measure! Enjoying music is subjective and emotional.

Indeed. I agree, but some technical knowledge or guidance from an unbiased person with the technical knowledge inverably allows us to cut a few corners, save a pound/dollar or two and lead us to a much refined set of choices when we come to select our choice of gear we prefer to use. Those of us who are technically ignorant really benefit from the guidance of those who understand, provided they are honest (not commercially connected in any way) and not inclined towards any aspect of marketing. The natural problem is those who really know are inconsequence employed within the industry exactly because of what they know. Finding an impartial expert willing to share what they know is often equivalent to finding a needle in a haystack.

[chrisc]

In our audio club we have a scientist who is the chief scientific officer for the Square Kilometre Array, the largest group of radio telescopes in the world, that are nearing completion in the Northern Cape Province of South Africa. He had two doctorates, one in electronic engineering, another in computer science

The reason I mention this is since this fellow never accepts anybody's word at face value. He inspects and examines all aspects of anything engineering-related when it comes to audio

Although he considers fancy cables to be of no theoretical value in terms of improving the sound of a system, we have shown over and over again that the substitution of a better (mains, interconnect, speaker) cable does have a noticeable effect on the overall sound. It appears to be cumulative, first the mains cable and plugs, then the speaker cable, each one helps a little, in small increments

We have not been able to duplicate this phenomenen with USB cables. However, there is (often, not always) a difference between using a USB cable of any sort (not a cheapie USB printer cable, but a decent one costing perhaps the equivalent of £20) and a Cat-7 LAN cable.

A room-full of listeners, who were not informed in advance of what we were doing, could detect (some) difference, but were not always able to put their fingers on it

I have tried various permutations of AudioQuest. I figured that robustness and accuracy of construction was the primary consideration. There are some inexpensive, well made and shielded USB cables using decent quality copper made by "Lindy". I'm using their Gold one and it seems very good to me

[ogs]

Is the Square Kilometre Array a HAARP installation?

[chrisc]

No, it just a linked array of about 120 radio telescopes. Some European Union agency is sponsoring it. The budget increases annually. It is currently €1.2 billion

Each of the telescopes must be aimed at exactly the same point in space. One of my friend's tasks was calculating the time difference between telescopes that might be up to 1.4km apart, since radio waves from space arrive at different times (millionths of a second) at different dishes. There was a lot of maths involved. I thought I was good at Calculus and advanced maths but got lost on page one

A big problem is "noise" from television and mobile phone signals. That is a why a large unhabited area was chosen. It is 40km from the nearest small town, yet there are bands in the 120MHz to 500MHz range and also 1900MHz range that cannot be used. It has taken an act of Parliament to shut down these transmitters

I have been there twice. The staff there seem to speak a different language

http://www.ska.ac.za/

[ogs]

Thanks, interesting

[K4680]

The German HiFi Online magazine "HIFISTATEMENT" creates various files ready to compare the same usb cable with different directions!
I'm curious to see what comes out of the tests!

Compare the four files and analyze what you heard. The letters in the names of the files indicate the direction of travel.

The files can be found at the end of the article.

https://www.hifistatement.net/tests/item...-usb-kabel