No disrespect intended. But if you think I was being sarcastic, have a peek on the Roon forum re ethernet switches and cables. Some wild and witty sarcasm there.
And I mean it when I say that you have exceptional hearing: in a synergistic system, such as hifi gear, to make a small modification and hear an “immediate and positive effect”, now that IS exceptional!
This should worry people over at dCS, because it means that their products are badly designed – can’t even deal with puny electrical noise.
I can only comment on my experience and I can’t speculate as to why they would deny the benefit of a switch.
I did follow their recommendations though and purchased the cat 6 cable they recommended but I found another certified and tested cat 8 cable to be better.
How’s your experience with the cables?
As I said before, I do not have exceptional hearing, some differences are very audible.
I do have a relatively transparent system though and the flipside is that I can pick up unwanted noise more easily, and my system is relatively new so it’s still maturing and improving. It’s trial and errors.
I just want to share an anecdote. A couple of weeks ago, my brother in law came to spend a few days.
He had issues with internet, so I activated the wifi on the ISP provider router.
I couldn’t listen to the music anymore, initially I didn’t put two and two together.
When he left I turned it off and the sound came back to normal. It was very aggressive with the wifi on. Like rough around the egdes.
Would you call this a dCS product flaw?
it’s not always black or white imho.
Sorry however this “fact” is not vastly accepted.
*and I assume by data chain you are referring to this thread topic ie ethernet
I’m sorry, but that’s just nonsense (the UpTone folks get away with talking nonsense because most lay people just don’t know how Ethernet actually works).
The Ethernet PHY layer operates the same way regardless of how long the Ethernet cable is. Naturally the longer the cable, the greater the signal degradation for decoding, but even a typical CAT5 cable used with a Gigabit Ethernet interface can operate normally at 100 meters.
Once an Ethernet signal (over copper CAT cable) is decoded at the PHY layer and data bits passed onto the Ethernet Switch processor (over the MAC/MII interface), the physical layer problems, i.e. length, noise etc. is completely irrelevant. Everything is handled digitally up the networking protocol stack from thereon.
I highly recommend you spend maybe just 30mins or so to educate yourself on exactly how the Ethernet PHY layer works. Here are two good relatively new videos from Texas Instruments - watch all of the first, and maybe just the first 10 mins of the second.
Full disclosure, I work for an Ethernet Switch manufacturer.
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‘Controversial’ and ‘tiny minority’ have no relationship to each other. Consider the examples of the last US president or the issue of abortion.
Personal experience is weaker than samples in empirical research. The individual reports here are still valuable for those who look for patterns. You use the word ‘objective’. I would at least call into question the usefulness of the concept of scientific objectivity for going about our audiophile hobby. Scientific objectivity seeks to eliminate biases, emotions and false beliefs for testability and reproducibility. Biases - I don’t care, it’s my free time and if I’m enjoying myself, where’s the issue. We are talking about music listening and that’s an emotional affair. Eliminating emotion doesn’t make a lot of sense to me. False beliefs - yes, as it would help in choosing better gear. Instead of objectivity I suggest using the methods of dealing with complex systems as the human body and mind are complex.
Occam’s razor refers to parsimony in scientific problem solving. Maybe you can explain how that relates to the issue at hand?
We arrive at this point regularly in our community. It feels repetitive. It really helps when we recognize the vast diversity of dispositions we all have. Just look at a beggar versus a king. Their lives are completely different and presented with the same information they would surely decide differently. Or look at an accomplished composer. His perception of music must be very different from mine. I’m actually incapable of creating music. Or look at the portraits of rock and pop musicians Annie Leibovitz shot for the Rolling Stone. I would never be able to create those. These are just analogies for how each one of us perceives music or sound in a different fashion. You might be interested in the books ‘Musicophilia’ by Oliver Sacks (where he describes ‘amusia’) and ‘This Is Your Brain On Music’ by neuroscientist Daniel Levitin.
Sometimes the dCS employees really hold back their feelings:
I’ve had that tab open on my phone for months now. Every time I see it I giggle.
I tried a mix of network things (cables and devices), and the only things that I’ve kept around are BlueJeans Cat6 cable, a GigaFoil and a Cisco CBS110-8T-D switch. The last two are both powered by a Keces P8.
Everything else I returned or sold. It was fun to try stuff out, but even more fun to have some more spending money after the tests were over 
True, and I should have phrased this more carefully. The case for audiophile ethernet switches and cables has been thoroughly debunked, so I should have said that a tiny minority holds on to scientific nonsense. As you mention Trump – ingesting bleach to protect yourself against Covid-19 is deemed a good idea by a tiny minority, but it’s hardly controversial, it’s just a crackpot theory.
I don’t quite understand what you mean by this. What methods for dealing with complex systems do you have in mind?
Nor to me. I don’t think I’m calling for the eradication of emotions
Here’s the first definition of Occam’s razor I came across on the internet: " a scientific and philosophical rule that entities should not be multiplied unnecessarily which is interpreted as requiring that the simplest of competing theories be preferred to the more complex or that explanations of unknown phenomena be sought first in terms of known quantities." If you need to decide between two theories, which one shall it be? In this particular case: the theory re ethernet switches for which there is no scientific basis whatsoever or the theory (self-induced illusion) for which there is a lot of evidence?
I agree and disagree. Sure, let’s have all sorts of opinions and dispositions. That’s a good thing, sometimes. Not so good when claims are made that have no grounding in any objective testing procedure. The very least I would expect is to mark these claims as highly subjective, because in the end that is all they are.
If any modifications you make to your system procures greater enjoyment, that’s great (for you). But in the absence of any scientific measurements, and sometimes in contradiction to established scientific facts, we’re dealing here with psychological ‘issues’ (no negative valence). Indeed, as Oliver Sacks among others has shown so well: our brain is such a complex mechanism, and this complexity manifests itself at times in our propensity to believe what we want to believe. That’s OK when it comes to hifi propositions, but when something more important is that stake, this propensity regularly leads to disaster.
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Many interesting replies here. Clearly an expensive switch can and probably does work. For similar reasons, I trialled and then bought a GC3 Ground Control box from Computer Audio Design. I’ve found it to have a quite remarkable and beneficial effect on all my equipment. This includes not only my hifi (Linn, Audio Research, Sonus Faber, Network Bridge) but also the TV AND (and this is a big “AND”) the TV and hifi equipment I have in other rooms. Removing all the electronic noise from the maze of circuitry that exists in my house has had an astonishing effect on sound and picture quality throughout. I’ve also upgraded the cables to Audioquest and these, too, have given improvements to sound and picture quality. I don’t think I need to go further and invest in a switch as well. The CAD ground control box has probably achieved (and more) what the switch is trying to do. Hope this helps.
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it’s my impression that the vast majority of people streaming have taken steps to optimise their streaming chain wether in the form of lpsu, switches, ethernet cables, filters, etc
And anyone willing to spend a bit of time on the topic can verify for themselves
Thanks Anup, I will take a look into it.
But I wanna point that I am really not qualified to discuss the technical side of it, I really have no clue.
I’m just here to report my findings after my experiments.
The dCS community has a number of vocal members who adhere to a hard science approach to high end audio. I am deliberately choosing to speak up from a more difficult position because I like the intellectual challenge. I stay in the debate as long as we are governed by intellectual integrity. That among other things means we abstain from simply resorting to or insinuating ‘higher authority’ ̴ ‘science’ or using semantics like the proximity of words to make a point. You did the latter twice - when placing crackpot theory close to ethernet switches and placing opinions right beside dispositions. Also mutual respect is vital. We have to speak at eye level. I am not going to be talked down to or pitied as the ‘whatever the flavor of the day is’.
My general proposition is that the narrowly understood scientific or engineering driven methods often argued for here have serious limitations when building an enjoyable hifi system. In a non negligible percentage of cases it provides pseudo-objective crutches that have unpredictable effects. If for example one looks only at data transmission over the IP stack the recommendation for gear can be suboptimal. This narrow perspective would not prescribe optical isolation. This view has been argued before and then at the same time optical isolation was used. That’s contradictory.
That’s the rub and what I was getting at. If you permit emotions in choosing upgrades you dropped an integral requirement for objectivity. Emotions arise in very different ways between individuals. As can be easily observed when studying reactions in a concert or in a cinema.
I am copying what is behind the hyperlink I provided above:
This framework makes a lot more sense to me than reverting to scientifically objective details that have the tendency to tell part of the story. Or to put it another way we are building a hifi system we enjoy. That’s different from the task an engineer faces in actually building the device.
I’m a computer scientist by training and a money manager by profession. The traditional engineering frame of mind is ill suited to complex systems. Financial markets are at the upper end of complexity when looked at as a system. So I have experience in both situations and believe to know what I am proposing.
I think you get Occam’s razor and the hypotheses wrong. Occam’s razor is a heuristic used when developing theories that has its place. It is by no means a universal rule. Basically it prescribes to prefer the theory that can survive with the least amount of additional hypotheses or complexity. Simplicity is not an end in itself but helps with testability and falsifiability. So first, you would have to formulate two hypotheses that have predictive power you want to judge against each other. Here your prior reasoning is too fuzzy to qualify as competing hypotheses. Plus you are convoluting the line of thought by introducing illusion.
As I said above, placing ‘opinions’ and ‘dispositions’ in a sentence like that is not permissible if we are having a valid debate. I myself can have an opinion about running a marathon. But I certainly have no disposition for running a marathon. Dispositions are our nature and then nurture is what makes them appear or flourish. Opinions are something entirely different.
On your last paragraph - I’m picking quotes to make a point.
“highly subjective” - “we’re dealing with psychological ‘issues’ (no negative valence)” - “propensity to believe what we want to believe”
First of all, empiricism works when studying minds. So does introspection and neuroscience. All three methods produce valid conclusions. Why is jitter being optimized? Because enough people perceive it as detrimental. Why do we have a choice when it comes to DAC filters in dCS gear? Because people have different sensitivities to the admittedly smaller differences a filter makes. If there were only one right solution, dCS would not give us a choice. With ethernet cables and switches I believe we have two issues at play. First, both interact with the house systems and how they are built. That will explain part of the variation in observations. Since dCS was no part of building my house, I go with what works in my greater ‘house system’. The second issue I already brought up. We have different dispositions when it comes to listening to music. There’s no better or worse, no higher or lower, no chosen or not chosen. Only different. If a man can mistake his wife for a hat or people can display ‘amusia’ (both Oliver Sacks) it should be quite obvious how different our minds are. There is no ‘normal’ that is identical for almost everybody and then outside of that are illusions, psychological issues and make-belief. We have custom. And custom is subject to mutual agreement and change. That’s about it. It is simply that only a percentage of people hear differences here. Framing these differences in perception as illusion or make-believe I find is a narrow minded view.
I take it that you see me as a member of that group. Actually, I’m not. I’m an academic who comes from literature and philosophy. I am, though, and unlike many of my colleagues, respectful of and attentive to evidence-based theorising.
I’m not aware of having invoked a higher authority. If by science you mean the hard sciences, I want to assure you that this is not my position. Science to me encompasses more than the hard sciences – as long as our truth claims are evidence based (and that evidence can very well have a hermeneutic/ interpretive grounding, as is the case for instance for much of Continental philosophy).
I certainly don’t want to create the impression of talking down to anyone.
This seems quite pernickety to me, as it doesn’t change the basic matter of the issue.
Possibly, and by this I mean that I’m not an expert on Occam. I’m well aware of the fact that Occam is usually credited with the idea of parsimony or simplicity when it comes to deciding between different hypotheses in relation to the same prediction. As applied to the case of ethernet switches, this can be formulated as:
Prediction: improved SQ
Hypothesis 1: due to ethernet switch
Hypothesis 2: due to other factors (as for instance self-induced illusion)
My conclusion is that given that H1 is scientifically untenable whereas H2 is scientifically tenable, we should prefer H2.
I agree that this line of thinking may stretch the applicability of Occam’s Razor, and that I’ve used the principle in a metaphorical way (my literary leanings), but I’m new to this forum and didn’t expect to be held to such high semantic standards. I’m trying to learn.
I permit everything when it comes to hifi upgrades. Even the colour of your amplifier or the shape of your door knobs if it makes you enjoy music more. But don’t expect those factors to be validated in any objective way.
Who is making an authority claim here?
Yes, but the effect of filters can be independently verified, i.e. not because of different sensibilities. The latter come into play as to how much you may prefer one filter to the other, but their objective impact, the fact that they have a measurable impact, is not subjectively grounded. That’s hardly the case with ethernet switches.
Now we are talking, Marc @poseidon77.
H2 - as it is - has an unspecified number of ad hoc hypotheses as it only says ‘other factors’. But which and how many? Occam’s razor would let us choose H1 because of that.
I propose different hypotheses:
H1: Perceived sound quality improvement is caused by changing the ethernet switch. Ad hoc hypotheses: (1) Only part of the listeners perceive the change as large enough. (2) Ancillary systems have not been standardized among survey sample.
H2: Perceived sound quality improvement through changing the ethernet switch is caused by self-delusion.
Occam’s razor would have us prefer H2, as it does not rely on ad hoc hypotheses. But would H2 fit a survey sample and prove its predictive power? You will notice that I introduced perception more prominently into the mix.
With these hypotheses we could go ahead and survey a sample of audiophiles and find out empirically. For that purpose we could debate how to structure the survey, or what percentages need to be reached to make H1 or H2 tenable. Also, we could argue about methods to employ in the survey to account for the possibility of delusion being the cause. As I see it, for H1, there would need to be a percentage above 5% of respondents including a check for sanity. These checks for sanity have been provided in the forum before - like letting a significant other listen or going back to an earlier configuration or simply the expenditure of upgrades. If we assume basic sanity and a certain level of education, people part with their money for good reasons. H2 is a strong statement. We would need to demonstrate that the vast majority of people who reported a positive change in sound quality are deluded.
In my experience there is a certain magnitude of effect a purely mental event can have. When I sit down to listen, after a while the music sounds better, because I have settled my mind into listening and distractedness has subsided. For others a glass or two of wine will do the same. That’s the threshold I would accept for self-delusion, not more.
You’re not reacting to three important parts of my above post. The tactics to deal with complex systems as a superior way to approach the hifi hobby and at the end the reference to empiricism, introspection and neuroscience to achieve valid insight. And last but not least the differences between individuals’ minds.
This discussion is very interesting. My job is doing research and teaching, and I am afraid that with hi-end improvements we are in a swamp where usual scientific paradigms do not apply.
Trying to design a reproducible experiment is hopeless, the quantity of control variables is overwhelming (and for some of them we have no control), and confounders (some of them due to legitimate subjectivity) are all over the place. I would never attribute a scientific value to any experiment conducted in this way.
So I gave up on classical Hypothesis Testing and developed a Bayesian approach.
I start with a baseline neutral level of confidence in a possible improvement due to an arbitrary component X: p(X is good). Then I update this value with all the information available (what I can find). Example: if there is a sound scientific rationale, p(X is good) increases, otherwise it decreases. If my ears are happy of what they hear, p(X is good) increases, if many people on the web (no reviewers, just passionate people) agree on how good X is, with no commercial mumbo-jumbo or pseudoscience, p(X is good increases), and so on. If there is a perfectly good scientific reason why an improvement doesn’t exist, p() decreases wildly, and so on. To give an example of this last one: when the seller says that a given Ethernet switch improves the accuracy of the bits that are presented to the DAC, or their timing over an Ethernet cable, this sends p(X is good) close to 0 immediately.
At a certain point, if the evaluation (which is always a distribution) is significantly far from the confusion area (in which anything could be true), toward the “good” area, where “significantly” must be weighed with price, then I reach for my wallet.
It works. It’s how I decided for some expensive cables, for the SPEC amplifier, for everything I have now, and I am pretty happy about that.
Of course, it works if one is well balanced. When you fall in love with some speakers, during the honeymoon you only see (hear) the princess, only to wake up one month later with a witch, and nothing can help you. But it’s part of the game, isn’t it?
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Ahhh, excellent, thanks for clarifying the real world pitfalls of hypothesis testing for hifi, @Zapp. So I probably have to drop that proposal. What I want to get away from is the rationale “lack of apparent explanation plus perceived improvement equals delusion”. This is not the case as our minds and how they interact with our sense consciousnesses differ greatly.
I believe it to be good to permit complexity in research. Complex fields like the human mind don’t lend themselves well to reductionistic research. Same as nutrition. The human body is too complex. The reductionist paradigm is mechanical in nature and resorts to simple causality. To state that A causes B it has to be true that (1) A always precedes B (2) B always follows A (3) There is no C that could also cause B. Simple models of causation can lead to unexpected and unexplained findings. Reductionistic research uses prospective experiments and case control studies. In contrast a wholistic evidence source is observational research. Contemplative science or neuroscience are others.
I really like your Bayesian approach. It simplifies in an apparently valid way. We had a loosely related and less scientific thread here:
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This discussion has quickly taken an epistemological turn. Which is interesting, but also makes it impossible to settle the issue of ethernet switches in a way that would satisfy everybody. After thousands of books and tens of thousands of articles, there is still no agreement on how we can be certain to know what we are talking about.
Still, just for the sake of it, I do want to clarify my reasoning behind some of my assertions.
It’s best to drop the whole Occam Razor thing. The concept (or heuristic tool) doesn’t apply here and/ or needlessly obfuscates the matter at hand.
So let’s start from scratch and anchor our discussion in a real life situation. I change my ethernet switch and I detect an improved SQ. What’s going on? In other words, I make an observation and would like to have/ formulate an explanation. Most of the time, I won’t really bother; I’ve changed something in my system and that has produced the desired effect. Case closed. Why spend time and energy on something that seems obvious? It’s like changing a defective bulb and wondering why the new bulb works.
In this case, though, I know that changing the ethernet switch shouldn’t make an appreciable difference. Ethernet switches and cables work according to particular data transfer protocols and those don’t impact a DAC negatively, unless they are badly implemented, but then the transfer wouldn’t happen in the first place or in a clearly deficient way, such as producing plops and stutter — that’s what science is able to tell me. And yet there’s a difference. I can hear it after all. I could explain this scientifically unexpected result in a variety of ways:
- I’m on to something — ethernet switches do make a difference
- (related) There are more things in heaven and earth, Horatio, …
- I’m imagining things
- A miracle (amplifies the Horatio hypothesis)
- Besides changing the switch, I’ve also moved the rug half an inch to the right
- It’s rained a lot recently and my electricity has gotten cleaner
- I’ve developed the magic touch
- A butterfly flapped its wings in the Amazonian forest
- The parrot has finally expired
- and so on (one could generate an infinite sequence of hypotheses/ explanations, only to be cut short by following the parrot to one’s final quietus.
None of these explanations can be cursorily discounted. I grant you that some of them will strike you as pretty wild, far out there (perhaps on the astral plane). Perhaps we can agree that 6) for instance is plain bonkers. But we will only agree because we inhabit the same world, in this case a world that we take to be governed by certain universal sequences of causes and effects. That’s not yet a scientific world view, as we would also have to eliminate 4) — no miracles allowed in scientific explanation. And so on — but perhaps at one point we will disagree and our worlds will begin to diverge from each other. That is one of the hottest issues in epistemology, sadly undervalued in much of the epistemological literature — the inescapable horizon of our explanatory models, that which grounds what we consider to have explanatory force.
I will posit, though, that we are both interested in evidence based explanations. And that means that we will only consider explanations than can be empirically verified (another issue here: what are the criteria for that verification?). 9) for instance can’t be verified as a dead parrot can’t be resuscitated.
To simplify and work towards a tentative conclusion, I will consider 1) and 3). That’s my world, my horizon, as somebody who discards purely subjective impressions as carrying sufficient weight when deciding whether a statement is true or false.
I already know that ethernet switches shouldn’t make a difference. But to allow for the possibility that they might, I will have to eliminate the possibility of 3). That by the way also accords well with Hume’s dictum that extraordinary claims require extraordinary evidence.
- is a scientifically reasonable assumption. We imagine lots of things pretty much all the time. It’s called confirmation/ expectation bias, priming, … How do we test this (as we’re interested in evidence based results)? As far as I can see, the only available test, one that would take into account the possibly very special hearing of mine, would be to have someone switch the switch (horrible pun) without my knowledge. Will I detect a difference in SQ after the switch?
(I also know that when we test new gear, we listen more carefully than usual. So we often hear details that had escaped us before, and we ascribe hearing those details to the new gear, although we should also consider the fact that we are just listening more attentively. This is a case not of imagining things but of false causative ascription).
In my case — as I know that 1) has been scientifically debunked and 3) has been clearly established through numerous studies — I will privilege 3). Unless clear evidence is produced that 1) might after all be possible. Such evidence will never come from testing every person who claims that ethernet switches make a difference. How could we possibly test everybody, in such a way as to eliminate biases? And that’s why we will happily continue to assert stuff that has no basis in evidence. We can’t ever be proven wrong, at least not conclusively.
As to not addressing certain points you’ve made.
- how to deal with complex systems — your recommendations are great, especially in the way of implementing protocols of courtesy and respect. But I don’t think they will be of much assistance when it comes to deciding whether a truth claim can be validated.
- the neurosciences — not my domain (I’ve only read up on that with regards to issues such as the self as an illusion or free will). Moreover, different neuroscientists say different things.
- individual minds — sure, our minds are all different to some extent. We have for instance different responses to different frequency ranges, but I’m not sure that this matters in our present case, one I take to be based on (self)induced illusion.
We will never agree, but that’s OK.
I think you wrote a lot of interesting things, especially “extraordinary claims require extraordinary evidence”.
Which is not too far from my Bayesian method after all, is it?
To remain in context: at baseline, I am pretty much sure that a switch won’t make any difference. In order to convince me that it does, I will need A LOT of SUBSTANTIAL evidence from my own ears, with different kinds of music, at different times, in my own system.
When some website says that their switch will improve the bitstream quality, sorry but it doesn’t work that way. I can’t buy it: there is solid evidence that this is not how things work.
When they say that their switch isolates much better from noise coming from different sources, I think “hm … that’s odd, there is supposed to be a galvanic isolation in the Ethernet card, but I might give it a try”. And then I will need some very adequate SQ improvement as before.
I don’t think we may expect anything more scientific than this …
And of course, there will always be people who buy alarm clocks, or magical pebbles (and will actually hear an incredible SQ improvement) and people who, for various reasons, refuse to accept that a dCS Rossini, or a top of the line MSB, sound definitely better than some 500$ DAC.
That’s just the way we are.
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Good, Marc @poseidon77, let’s agree to disagree.
These proposed tactics are not meant to be a validation tool for truth claims at all. They are the dance that is called for in order to successfully engage with complex systems (aka the listener’s mind in relation to hifi). They are a blueprint for going about our hobby - much like the Bayesian approach @Zapp put forward.
You might enjoy reading ‘This is your Brain on Music’ by neuroscientist Daniel Levitin.
It appears that it requires a certain level of contemplative experience to appreciate how very different our individual minds are. The usual view is ‘Mind? Yeah, it thinks, so what. It’s just a function of the brain anyway…’ Both not true. The reality is more complex, less reified. Western philosophy is limited in its scope here. That’s because the interesting findings come from insight beyond cognition.
Frequency range of hearing as an example for variability between minds is orders of magnitude smaller than the actual differences. The differences matter, because the way my mind interacts with my ear consciousness can very well be so different from yours that we both can truthfully describe the opposite experience (hearing improvement, not hearing improvement). Our moment to moment perception is grounded both in mental dispositions existing since birth and listening experience acquired during our lifetime. Moreover, what I listen for in music reproduction will almost certainly be different from what you listen for. Those are the real reasons why we have these debates. No illusion involved. My firm belief is, that dead parrots, miracles, rainfall, butterfly effects, wearing tin foil hats and so on are not considered an ingredient by any participant here. In other words I believe in the basic sanity of all involved. Plus experienced audiophiles know biases, self delusion and so forth and account for them. BTW, we are not debating coffee makers or pebbles in relation to hifi, we debate a component that is a direct part of the audio chain.
Unfortunately it is only hypothetical and I am back to personal experience. If you @poseidon77 and @Zapp came over we could compare. The cumulative differences in setup would be switch + LPS + power chord and maybe ethernet cables. I would change more than the switch, because then it becomes really obvious. All of the above changes should make no difference, because it’s IP traffic. So I believe all would be permissible in a test setup. I am confident both of you hear the improvement. If not, you would each get a box with six bottles of Louis Roederer.
Actually, in terms of testing there is little to lose but time and effort. Procure an audiophile switch (Melco, English Electric, Innuos), get a good power supply (Keces, Ferrum, Paul Hynes), a decent power cord and power distributor and try. The achievable result is a more natural, analog sound. Less of what is attributed to ‘sounding digital’. It won’t make a Bartók a Rossini. But if one enjoys the sound of vinyl, it’s worth considering.
If the only alternative to debunked is illusion, testing a switch upgrade is a waste of time. I give to consider that the comfort of the armchair might be the wrong place to resolve the issue…
Galvanic isolation is not as simple as that. The two sides may very well be isolated for DC, but at higher frequencies the capacitive elements of the physical isolation device come into play and the isolation is no longer perfect, hence HF noise may get through to the analogue circuits in the DAC (not the digital ones).