Why are digital streaming equipment manufacturers refusing to answer me?

I have performed double blind tests with the most highly regarded brands of streamers and some hifi switches. None have made any difference to my system on files saved locally. I have asked the following question to the makers of such systems and almost all have responded with marketing nonsense. 
My system uses fiber optic cables. These go all the way to the dac (MSB). Thus no emi or rfi is arriving at the dac. On top of this, MSB allows me to check if I receive bit perfection files or not. I do. 
So I claim that: if your dac receives a bit perfect signal and it is connected via fiber optic, anything prior to the conversion to fiber optic (streamers, switches, their power supplies, cables etc) make absolutely no difference. Your signal can’t be improved by any of these expensive pieces of equipment. 
If anyone can help explain why this is incorrect I would greatly appreciate it. Dac makers mostly agree, makers of streamers have told me scientific things such as “our other customers can hear the difference” (after extensive double blind testing has resulted to no difference being perceived) and my favorite “bit perfect doesn’t exist, when you hear our equipment tou forget about electronics and love the music”!
Its incorrect because its wrong. Your whole premise is false. Its not anyone's responsibility to explain to you why they hear something. Maybe its nothing more than they have learned to hear something you have not. Did you ever think of that? 

Not that it matters. Again, no one owes you any explanation. Not only wires, I can tell the difference between lots of things- wire on the floor vs elevated, wire going one way vs another, warmed up vs cold, on springs vs cones, on and on. And on.

But anyway, I can tell you why nobody replies. It was clear to me in the first 6 words: "I have performed double-blind tests". Because here's the thing. And I know this is hard to believe but think about it a minute you just might get it. When the difference between two things is so readily apparent you hear it immediately, why would you then put yourself through all the incredible time and effort to perform even one double-blind test? To prove to yourself what you yourself already know you heard? Why? 

You know the answer: you only do the test when you can't hear any difference in the first place. 

That is why double-blind testing is so illogical. They ones who can hear will never do it. And the ones who can't never will hear a difference anyway. All double-blind testing can do is activate another audio canard, the expectation bias.

I really do hope that one day you somehow develop listening skills and are able to hear differences between things like this. Seriously. I do. But until then, and for as long as you stay on this unproductive course: You go, girl!
Your blind tests prove one thing only: that YOU cannot hear any difference. Your ears, and with YOUR equipment/ in your room. Simple.
I had a similar experience when conducting ABX testing with amps (with all other pieces of electronics, I was able to select the proper item -cables and components - far better than 50% of the time). The only component that was not discernible in level matched ABX was the amp, which was shocking to me! The most bizarre aspect was that it was not possible to score well in ABX even when the amps being compared were SS vs. tubed! 

These results were written up by myself for Dagogo.com, as I reviewed the Audio by Van Alstine ABX Comparator. It was a fascinating experience, and I'm glad I took the time to explore it. Van Alstine agreed with my results, even with the aspect of the difficulty of distinguishing between amps in ABX. 

However, and this is critical, the similarity between amps was only when conducting ABX. Apart from that particular condition, or when reverting to normal usage in an audio system, the differences reasserted themselves. Therefore, I concluded that: 1. ABX is not necessary to establish differences between gear, 2. It does not represent real world conditions of listening, and has quite limited applicability to it, and finally, 3. That we have phenomenal ability/sensitivity to perceive minute gradations sonically, but poor short term acoustic memory. It took a LOT of concentration in a custom room with very low noise floor to conduct the ABX testing with accuracy.  

Consequently, after conducting my own exploration, I am content to spend less time thinking about ABX, and more time building better audio systems through very active, hands on methods.

Finally, I have done comparisons as well with DACs that were said to not yield differences of upstream components due to them being "bit perfect", etc. However, I did not find that to be the case. Whether they would be similar to amps, or not, in ABX testing, I do not know.  :) 
I expect the op is trolling, but even if they are not, the op should know they will get keyboard warriors jumping in to insult their hearing, their equipment, etc. however, I am sure the op knows that not one valid explanation will be coming.  The people most likely to be able to offer you an explanation for a difference will also be the ones that will read the ops post, and say "obviously", because absent electrical noise, and absent bit errors, there is no reason for one streamer to sound different from another unless they are manipulating the signal.  I am not opposed to them manipulating the signal, more power to them if people like the result.  Of course, the data interface is not the only place that noise can get in, but most high end servers are more power hungry than small servers, and EMI requirements (if met) only start at 9KHz or 150KHz leaving lots of room for grunge on the line.

Nope, when you use fiber optic, assuming no bit losses, which is very very easy in the home, then all those other things really don't matter.  However, you are attacking peoples preferred view of how things work, so you know what the results are going to be.
Congratulations Douglas_schroeder on having the courage to go on record with the facts to back up what we all (who can hear) have known for years. 

Consequently, after conducting my own exploration, I am content to spend less time thinking about ABX, and more time building better audio systems through very active, hands on methods. 

Beautiful. Lotta work to get to where we all knew you should be. But you did it, and you got there. All that counts. May others learn from your experience. Don't hold your breath. But would sure be nice.
If there is a keyboard warrior, that’s you @audio2design
You that keep coming over and over, and over after they banned all your previous fake accounts, AtDavid, Dannad, Roberttid and many more. Get a life dude

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I expect the op is trolling, but even if they are not...

pot stands up on hind feet, calls kettle black... ???

No trolling here jjss49, calling it exactly as I see it.  The op, at least as stated in their post, created a system that is electrically isolated.  It is also bit perfect (like most home networks).  There is no timing information in the signal .... and he did not hear any difference between streamers, exactly as would be expected because he created a situation where, short of data manipulation, there is no difference. It is not rocket science to pull data off a storage mechanism and serve it up on a data link without bit errors.

Note the author is also using an MSB DAC. I think we can agree that MSB is a competent enough company to design a DAC that does not experience any noise pumping from data arrival. It's not hard thing to do.

So, given the scenario that the op has presented, assuming no data manipulation in the streamer, the only logical and reasoned conclusion is that there is no difference as there is no mechanism to create a difference.

However, as expected, even in the face of a solidly presented case, it is a given that some posters will jump on their keyboards and attack the ops listening abilities or some other facet of what was done.  Was I wrong?
Oh please... MSB DAC for you 🙄. Now tell me why DACs matter and why anyone can be happy enough with a $50 DAC from China 🙄
If "A" reveals 8 out of 10 words of a lyric and "B" reveals 10 out of 10 words of a lyric, then an A/B test will let you hear all 10 words on A and B. 

There is an assumption that the human ear/mind system is a skilled comparator of sound, but it was designed to interpret and learn-- not compare.
If someone answers the question to your satisfaction, they are probably just humoring you.   So I would not lose any sleep over this unless what you are using does not sound good. 
So I claim that: if your dac receives a bit perfect signal and it is connected via fiber optic, anything prior to the conversion to fiber optic (streamers, switches, their power supplies, cables etc) make absolutely no difference.
It is simply not true.  Fiber optics transmitters are slow - about 10x slower than coax drivers.  System electrical noise makes those light transitions noisy (jagged), that in effect results on receiving end as a variation in the moment of level recognition (threshold) - a timing jitter.  This jitter translates pretty much to noise added to music.  That's why most often coax works better than Toslink.  You might not hear the difference because your DAC has very good jitter rejection, because your system has limited resolution, or simply because your hearing is not that good  (mine is getting worse).  Whatever the reason is - blanket statements are never useful.
Why is the troll refusing to answer us? Crawled back into his cave I suspect.
"...after they banned all your previous fake accounts,"

How does one make a fake account here? Are electroslacker and mapman real names? (nothing personal, those are just two most recent ones above so I picked them)

At least thyname is undisputably a name.
Glupson my man. My username is all there to see. Since 2004 or thereabouts. With all trading history here. And my actual gear under “system”. Let me know what else I can do for you.

A fake account (for like at least five times that I know of, maybe more) like our genius here goes something like this:

1) Create an account here. Post your hatred towards members, get kicked out (and rightly so)

2) Use another email address to sign up under a different username, as the original one was already taken. Post same venom. Get kicked out again.

3) Use another email address to sign up under a different username, as the original one was already taken. Post same venom. Get kicked out again.

4) Use another email address to sign up under a different username, as the original one was already taken. Post same venom. Get kicked out again.

5) Use another email address to sign up under a different username, as the original one was already taken. Post same venom. Get kicked out again.

6) Use another email address to sign up under a different username, as the original one was already taken. Post same venom. Get kicked out again.

7) Use another email address to sign up under a different username, as the original one was already taken. Post same venom. Get kicked out again.

8) Repeat

@kijanki ,

Unless I am mistaken (definitely could be), as the op was talking about networking connections, I believe he means fiber optic network I/F not fiber optic SPDIF. As well MSB offer fiber optic isolated USB I/F.

TOSLINK is typically slow, the ST based fiber optics interfaces are much faster. Of course it is possible to create fiber optic interfaces as fast or faster than electrical I/F because of the lack of interference.
I can provide some clarification on what you are hearing. My experience comes from developing communications and signal processing software. Including developing custom Ethernet drivers for signal processing.

The following discussion is for the analog transmission of a digital signal (PCM/DSD). Specifically Ethernet cables and switches. Note it does not apply to the analog transmission of analog signals (ie interconnects and speaker cables.)

An Ethernet frame is transmitted as a series of pulses. The transmitting Ethernet transceiver will generate a pulse for each bit in the frame. The receiving Ethernet transceiver will transform each pulse into a 1 or zero bit. The bits will be accumulated into a frame and the checksum validated. If there was an error in generating the correct bit value from a pulse then the Ethernet transceiver will request a frame transmission. If there are no errors the the frame, its contents will be copied into some form of buffer data structure. Processing on those buffers will be initiated by an interrupt or polling algorithm. At this point in time you have an exact replica of the original transmitted signal.
The well tempered computer dot com web site has a graphic depicting a pulse signal. It does not depict the aberrations in rise time introduced by clocks/crystals. If any of the pulse problems (overshoot, ringing, droop or undershoot) caused by EFI/EMI or clocking errors result in a bit error then the frame will be re-transmitted.

So you are correct that well designed Ethernet cables and switches do not effect the quality of the sound. If the receiving device (DAC/streamer) allow electrical noise from the Ethernet cable to affect the sound then you have a poorly designed DAC/Streamer.
Also one should not confuse Toslink with Ethernet fiber optic cables they are completely different animals. Note that an electrical signal on an Ethernet cable will travel about 1/100th the speed of an optical signal on a fiber optic cable. Fiber optic cables are used primarily for speed and system security. They will not make a difference in the sound quality.
@welcher This is a nice explanation of file data transfer. How about streaming, such as TIDAL, TV sound, etc.. You cannot go back and retransmit so there must be some occasional loss or imperfections. For music I assume it is not as catastrophic as it is for data files.

Your statement on fibre not making any difference in sound quality is challenged by products like the Sonore Optical Rendu. Their claim to fame is that the fibre cannot transmit any analog noise that exists in some level with Ethernet (maybe also USB). Thus without fibre, analog noise can get into the DAC.

@milalis I was going to buy a Sonore Optical Rendu today but changed my mind and will get a DAC with built-in streaming for occasionally used  bedroom instead (Black Friday sales). I am of the opinion that streaming with fibre levels the playing field. Using a noisy computer is also not a problem with fibre in the streaming chain. My current streaming, a microRendu, is more than good enough. So today, a second DAC will get me more short term joy but going fibre in the main rig is the long term plan for that final streaming solution.

Depending on the protocol / app, most audio over ethernet will retry, and most buffer to give time for retry.  If streaming locally, odds are you almost never need retry.
Audio2design, You're right - that's probably what he was talking about, otherwise it doesn't make any sense.  He says "My system uses fiber optic cables. These go all the way to the dac", hoping that optical connection, shielding DAC from electrical noise, makes incoming music always the same.  It is not why it is the same.  Streamed music doesn't come in real time.  It is just plain data that is pre-buffered.  As long as it is the same data in the same format everything depends on the hardware that creates S/Pdif stream/timing (and I assumed he uses different hardware for different providers).  What makes different streaming providers sound the same is the fact that they send data only. Asking them why it sounds the same (with the same hardware and the DAC) is like asking different bookstores why the same book looks the same.

It should sound the same, assuming same internet provider and hardware, same data, same data format, same streaming hardware, same DAC etc.  "Should", because there might be something else that I'm forgetting.

I looked at Toshiba Toslink drivers.  There are some, perhaps older generation, that go only to about 5 Mbit/s, but they have newer drivers that go over 100Mbit/s.  Such Toslink devices should suffer less from the system noise.  Jitter induced by slow transition time and noise at the receiver's (DAC) end would be reduced as well.
As the study of psychoacoustics evolves, it is becoming abundantly clear that A/B tests will become irrelevant. 

i have no affiliation or specific knowledge of thyname, or most other folks who post here

but when i think someone is trolling (not thyname, but someone thyname is pointing out):

-- i click their username and then check ’details’... one can then see when they joined, how many posts they have started or responded to since joining
-- one can also see if they posted info on their own system, and/or pictures of their listening room
-- finally, one can click ’marketplace feedback’ on the profile page ... and see what their track record is trading on the a-gon main equipment site - how many transactions over time, how many buys and sells, comments/feedback etc etc -- this is most important, a measure of the member's history, 'realness' and reputation not as a poster, but as a real person buying and selling equipment, with their real identity revealed to those they transact with

trolls often have

-- a very recent join date
-- a very large number of posts since joining (then you click on those posts, they are argumentative or instigating in nature...)
-- no info on their system
-- no track record whatsoever on the marketplace
Some clarifications
1) the fiber optic cable is what carries the signal. This provides even greater isolation than a cat cable, in fact as far as I know perfect isolation
2) the double blind tests included four people not just myself including a dealer who had to admit the lack of any difference

Someone referred to blanket statements not being helpful. I am not making any such statements. I am making a hypothesis, I test it, and I ask the community here to help with additional knowledge. 
My thanks to those who have responded on the topic.
Jdt1, why are a b tests becoming irrelevant? Any of us who have read o toole’s book consider his work to be seminal in helping understand real differences but is there something more recent that suggests a b tests if properly conducted include bias? Thank you.
yyzsantabarbara from what I can tell this would be a good choice and a less expensive way to get bit perfect signals. If the dac is equiped for it the cost is minimal and one can run very long fiber optic cables. If the dac can’t I have read of people buy converters back to usb right before the dac and again get great results with a very short usb cable in the end. M. 
Hi Welcher. My understanding is that Ethernet sends in packets but since it is still an electrical signal it is possible it would affect sound although a well designed interface is unlikely to. Usb connections are proven to make a difference good or bad with measurements. 
One designer of streamers confirmed that his effort is to reduce any emissions via air, cable and power. My “strawman” above addressed cable. I don’t know about air especially since fiber allows us to move the streamers or NUC as much as a kilometer away! About power however I get the point. That could have an effect. The way I may have indirectly dealt with it is that I run the custom nuc with a linear power supply (150$ from China!) and I always isolate my front end (other than the nuc) with isoclean or balanced transformers. M. 
One of my good friends recently became an audiophile and has finally agreed that the most important variable is actually what you hear not what science tries to prove. 
HI yyzsantabarbara

Both Qobuz and Tidal use the Rest API for streaming. The following is a generic example of a streaming session using Qobuz/Tidal; Audirvana and a streamer/DAC using UPnP/DLNA.
Audirvana will issue a REST request over HTTP to the Qobuz/Tidal server. Your computer will create an TCP/IP connection to the Qobuz/Tidal server and transfer the request after the connection is established. Your computer will also use Ethernet to transfer the HTTP, TCP and IP protocol data units to your router for transmission over the internet. The Qobuz/Tidal server will respond to the REST/HTTP request over the TCP/IP connection. Once the response is complete the TCP/IP connection will be closed.
TCP/IP will provide error free sequenced packet delivery between Audirvana and the Qobuz/Tidal server. If any packets are lost it will automatically re-transmit them. Ethernet will provide error free frame delivery between your computer and a switch/router.
Audirvana uses the UPnP protocol suite to transfer the media content received from Qobuz/Tidal server to your streamer/DAC. It will use HTTP, TCP/IP, UDP,  Ethernet and other protocols.

You will get error free delivery from Qobuz/Tidal to your streamer. There can be reduced band width on your connection due to network congestion/errors.
Pased on the elegant prose in your opening statement, I have no idea.  It's not as you sound like a rambling nut case or anything.
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Btw the designer of maybe the best steamer finally confirmed my straw man assumption. Turns out indeed it was correct. The signal is identical. No one can hear any difference.Of course I wouldn’t question that the person who was very offensive for no obvious reason earlier would hear differences from these identical signals from up there at his high horse. M.

@mihalis I called your post a "blanket statement" because you stated that nothing makes a difference when your DAC is connected thru fiberoptics etc.   There is a big difference between saying "I cannot hear the difference" and "Nobody can hear the difference".  There are many factors involved, including receiving hardware and the fact that your DAC is connected by fiberoptic is not changing anything.  I can only agree that with exactly the same data received in exactly the same format in exactly the same hardware to the same DAC - sound should be the same between providers.
Hi kijanki, thank you for the clarification which I understand. 
My statement was a straw man assumption which I put forward for us to debate. It is “absolute” on purpose, like a math equation that we are trying to prove wrong. Sorry if I wasn’t clear about that and it sounded like I was saying that I know it is correct. Which I don’t.
The revised statement which is now informed by further feedback from two designer experts is that so long as we receive bit perfect signal via fiber optic cable through a converter that is clocked to the dac we get a signal that can’t be improved with expensive streamers. One said “everything before the conversion doesn’t matter at all”.
Some other arguments against this include that one may be introducing electrical noise to the house’s electrical system before the fiber and also that one may be introducing airborne ref. I suspect these are negligible in real life conditions especially as one can move the server to another room.

I repeat this is an assumption for debate although we now have many facts in its favor. And I hope it helps people save money and focus their spending on equipment that matters. 
What I am baffled by is 3-4 responses which were not only rude but also paradoxical: bashing an effort to emulate the scientific method whilst using such science based equipment. Maybe it’s the snake oil they put on their salad. 
All the best and thanks to those who tried to explain and help. M. 
Also reading the earlier confusion about fiber optic. My bad, I didn’t want to detail the system and I should have had. I receive streaming via fiber and also play audio from local drives. All this is irrelevant to my point. My reference to fiber is only as it relates to what happens between the Roon core and the dac. My Roon core is home made and via usb it goes into something called usb pro which is basically msb’s conversion from usb to fiber optic cable. This cable then feeds the dac directly. I was only referring to this connection and not to the ISP. My understanding is that usb pro is clocked to the dac’s clock. And my search has been to figure out if I can improve on my home made nuc with expensive or well reviewed streamers. Stereophile just had such a review where the writer who seems quite honest clearly says that he can’t ascertain any audible differences. 
Hey @mihalis I had the same MSB DAC, but the lowest model, the Discrete with the same ProISL / ProUSB module combo like you. At that time, there was an audible difference to my ears when feeding that DAC via USB from a NUC, then Nucleus, vs. a top server ‘ streamer I had then, the Innuos Statement. That’s what I heard, with my ears, my equipment, my room. That’s all I needed to know, and be happy, enjoying my music. I did not have to worry why, although I intuitively can figure out the reason, based on what the Innuos Statement has / does.

All what matters is we experiment for ourselves. Sometimes new things work, sometimes they don’t. We then move one to something that works, or just stay with what we have / own. It’s pretty simple. 
@mihalis  yes, asynchronous USB receives just data and uses own independent clock for D/A conversion.  Still, any electrical connection can inject noise and alter this clock timing.  As for optical connection - it helps, but it is not a panacea.  Bits are still bits but timing of arrival can be altered.  Any system noise can make transition (including light intensity) "jagged" varying exact moment in time of level change recognition (threshold).  I don't know how to explain it better, but let's try this - Imagine in slow motion filing your tub with water.  It supposed to stop when crossing certain fill level, but water have waves (noise) and every time you repeat it - it stops a little bit sooner or later. That is time jitter.

Perhaps you know all this, but imagine that you receive 1 kHz pure sinewave.  Big electrical noise added to signal is causing different moment of level recognition and stream to "vibrate" in time.  When words fed to D/A converter vary in time then it will result in creation of additional signal - sideband frequencies.  When 1kHz stream delivery vary in time by 20 milliseconds (50Hz) the output of D/A converter will produce 1000Hz, 950Hz and 1050Hz - three frequencies instead of one (and many more at lower levels).  Amplitude of these additional signals will depend on range of time vibration, but it is very low.  It is still very audible, since not harmonically related to root frequency.  Many noise frequencies and many offended frequencies (music) results in added noise - less audible for random jitter (uncorrelated) than jitter induced by particular frequency (correlated).
As for a USB streamer, I wanted to clarify the “clocking” part on this discussion, based on what I researched and experimented with back then (I no longer use USB now):

Yes, the AUDIO SIGNAL on the USB streamer is “clocked” by the DAC. No question. A good USB streamer reclock the USB signal, not to be confused with the clocking for the audio signal. It is reclocking the USB commnunication between the source and the DAC, meaning it does not work at the audio level but at the USB protocol level.

I don't think people realize that the USB signal does not get reclocked by the DAC. What they reclock on the DAC is the audio signal that is transported via USB. The USB communication components themselves (I.e in a USB streamer) are affecting the performance of the DAC. This has also independent of the galvanic isolation of the DAC, which on its own is a separate, independent issue.

I hope this makes sense @mihalis . Needless to say, theory is just that, theory, and not a substitute for practice.
I assume you meant prousb and not usb? Did you run bit perfect tests to ensure you were comparing apples to apples? 
It is encouraging to hear you got improvement and that it was pretty simple. Would you mind elaborating how you can intuitively figure out the reason based on what the innuos statement has / does? 
I don't think people realize that the USB signal does not get reclocked by the DAC. What they reclock on the DAC is the audio signal that is transported via USB.
In async USB DAC receives "frames" of data usually at 1kHz rate and feeds them into buffer.  It signals back upon buffer under/overflow to adjust size of incoming frames.  It is data coming in - not "audio signal".
Hi @mihalis yes, it’s the ProUSB / ProISL combo:


It’s the two part combo (scroll down on that link above):

  • Pro ISL Input Module
  • Pro ISL cable
  • Pro USB
That’s what I wrote on my previous post, no? Is this not what you meant?

Some really good points about A B which I will address here. Since someone attacked my person for some mysterious reason, I am forced to explain that these tests were always done with a group of experienced audiophiles in Asia and in Europe. To them we added some friends who aren’t audiophiles to make sure we don’t have any bias from that. We did double blind tests, not triple blind. The groups were not the same always. And the tests were two hour affairs on occasion and not some extensive lab test. I am claiming nothing other than what this meant for us. 
The post earlier about how the ear isn’t made to compare is I believe correct but our methodology probably eliminated this bias. 
First we listened with knowledge of what equipment we are hearing. Then we listened to equipment which was given a code (not A or B but eg 346 and 589). And finally we listened to unidentified equipment in random order and asked to identify which code it was. 
Various pieces of equipment had different success because many obviously do sound different. But with equipment which shouldn’t really make a difference according to some logic, we had the following results

1) consistently, expensive equipment was identified as better and we could all elaborate that we heard specific differences. I certainly did think so

2) consistently, when the equipment was labeled, we could not necessarily say if it was overall better or not than the other but we developed certain characteristics we each thought we heard. These characteristics were not consistent between each listener but the same for each listener

3) not one person was able to identify these differences with more than 20% consistency vs 1 or 2!!!

Take me out of the equation since I am apparently a troll. The people in these rooms are audiophiles with significant experience, from different cultures and of different ages. We were stunned. (Non audiophiles usually abandoned us after 30m).

What this meant for us? If we smell something doesn’t make sense, we look into it so that we don’t end up spending our savings towards the wrong equipment or system. Ie we try to reduce bias. As a result we feel we have better systems with less equipment and less cost. 
This is how this worked for us. I am sure everyone has their way and I am not making any broad généralisations about anyone else. I did feel validation when I read the seminal work of o toole and some sites which do measure equipment extensively with correlation to performance potential. 
To each their own, although I hope at least some of you may consider these points.

troll out!
Thyname you wrote feeding via usb and I wanted to be sure that the prousb conversion was involved. So if you know more about how your streamer would improve the signal it would be great to hear it. It goes against what msb and other steamer makers are saying but maybe there is something they are missing. I haven’t had the opportunity to listen to this steamer, looks terrific.

kijanki much appreciated. Exactly, I am focused on the fiber connection because it eliminates all electrical interference. What I struggle with is that since the signal is bit perfect and the fiber eliminates noise which would have affected the dac, wouldn’t we be getting data = what was sent? Thanks again, getting late here in Europe. 
Thyname thank you for the more extensive response which I hadn’t seen until now. Going for that bath now! M.
@mihalis I simply shared what I experienced, with that MSB DAC and that same module. Which MSB DAC did you own? I don’t see it under the System for your current gear. So for the ProISL / ProUSB module combo, was it the same you had? That’s what I had.

My subsequent attempt in technicality of the benefits of USB protocol in streaming (or lack thereof) was simply based on my limited technical knowledge. I don’t pretend to be fully able to explain everything I hear.

As for the MSB ProISL / ProISL implementation, yes, the main objective is to eliminate copper, therefore the electrical interference associated with it, by introducing fiber. But it’s not as simple as that. The first device, what they call ProUSB (the dongle that stays outside the DAC, on it’s own) converts USB to their proprietary ISL audio transmission via the fiber. Then the module that goes into the DAC, what they call the ProISL module, is the one that is directly connected to the DAC architecture. Basically copper USB cable to the ProUSB dongle input, then fiber optics cable from the ProUSB dongle output, to the ProISL module (attached to the DAC) input.

So it’s not as simple as fiber, and here you go, all problems solved magically. The conversion itself is perhaps just as important, as in theory can introduce other issues.

Further, many of the non-believers will tell you that any of that is not an issue at all, and any competent Topping China $50 DAC has all that built in, galvanical isolation and all, so totally unnecessary to go through fiber they will tell you. So here is that.
The test you did Mihalis sounds well thought out and the results exactly as expected.

It is possible for the incoming data stream to impact clock timing but that would be expected in a poorly constructed $50 USB DAC from China not an MSB, not to mention the pro-ISL fiber does not communicate USB.

There is also no guarantee that thyname's high end streamer does not manipulate the bit stream or that what he compared it against manipulated the bit stream and the one he prefers does not. We like magic and so we hold on to the magical explanation when the more likely one is almost always right.

Keep in mind a lot of high end components are intentionally euphonic and their euphonic signature dominates their sound not necessarily their technical competence.