Objective-Fi Optical Networking & SFPs

[cat6man]

i don't want to derail the topic, but this seems to be related (at least to me)

 

what if we back up a bit.  forgetting for the moment sfp variations and if/how they are real, what about basic galvanic isolation?  do we agree that it is real and a good thing?  if so, how can it be measured?  has anyone done so?

[cat6man]

1 hour ago, plissken said:

 

Optical by it's nature is galvonically isolated by the fiber run. The thing some people want to put their head in the sand over, especially at 10G, is that the engineering standards for it even to work require incredibly low jitter. Then you have to consider that fully realized 10G is 1250MB / Second. That is 48MB every 1/60th of a second. That is, on average, a 16/44.1 PCM track in 1/30th of a second transferred to a system that would say have 256MB of buffer. 

 

The PRAT, airieness, extended highs, better slam? It's all out of buffer while that connection just sits there IDLE. 

 

yes, i know.  i'm asking if the isolation of fiber can be measured relative to copper ethernet which is not isolated.

can the isolation aspect specifically be measured?  i'm not talking about sound or PRAT or air or buffers, but simply "can the isolation of fiber" be measured somehow?  objectively, how is that done?

[cat6man]

26 minutes ago, cjf said:

I wouldn't think there would be a need to measure the isolation of fiber as it is absolute by default. In other words, the medium used to transmit the 1's & 0's from point A to B is not conductive and the light traveling thru that medium is also not conductive so isolation would be absolute and total

 

guys, you really don't get my question (and i'm really not trying to be cryptic or difficult here)

 

i understand fiber is isolated.  replace the fiber with copper (not isolated).  what would i measure that would not be there with fiber? (i.e. the objective benefit of isolation if it exists)

 

measurement A (with copper, no isolation)

measurement B (with fiber, provides isolation)

 

A-B=benefit of isolation/fiber (assuming fiber isolation provides an objective measurable benefit)

 

so what would the 'measurement' procedure be?

[cat6man]

36 minutes ago, plissken said:

 

Far as I'm concerned would be single or multi-tone test from DAC output into a very good ADC. 

 

has anyone done this to prove or disprove that fiber isolation helps?

[cat6man]

34 minutes ago, cjf said:

Maybe the simplest  test would be to grab your favorite AM/FM clock radio or similar and tune into an AM band without a radio station, turn up the vol a bit and run the antenna near the cat based eth cable first and listen to the hash, noise...etc then do the same to the fiber cable.

 

You would have to be measuring the cables themselves and not the termination points as that is were the elc connection starts for both cable types.

 

simple but useless to evaluating if we might be getting an audible and measurable difference.

[cat6man]

5 hours ago, cjf said:

I see. So the person asking everyone else how to conduct a test and measure results because "they" dont believe there are isolation benefits to using fiber is now all of a sudden qualified to judge if a proposed test has any value. Interesting.

 

nope, you still have it wrong.

 

i, in fact, do believe it but the test you propose is too artificial and contrived to prove that it has a benefit on a reasonably well designed and configured audio system.  i have no doubt that it is not good running a copper wire past my microwave or a power saw, and that a fiber connection would have more isolation or immunity. 

 

@plissken had a reasonable suggestion for a test but unfortunately i do not have test equipment available.

has anyone done a test as suggested by @plissken?

[cat6man]

On 6/20/2020 at 9:06 PM, plissken said:

 

Far as I'm concerned would be single or multi-tone test from DAC output into a very good ADC. 

 

i personally define objective proof in audio as requiring measurements that confirm a hypothesis.

i do not include blind or double blind testing as 'objective' (your mileage may vary)

so let's continue on my version of a possibly 'objective' answer.

any engineers or scientists here?

 

i'll assume the audio precision top end stuff is sufficiently accurate (correct me if that is not right).

 

now, can the audioprecision (or other) equipment collect a histogram of DAC output as well as instantaneous peak errors or just averages?  when it plots snr vs. frequency for a single or multi-tone test, can it save peak or just average noise?

 

if so, can anyone point me to published material where the average vs. instantaneous and peak distortions are shown?

[cat6man]

11 hours ago, bluesman said:

As a tenured professor at a university medical center, I and my colleagues rely on DBT as a valid research tool.  Well designed, properly powered double blinded clinical trials have been the basis for many major scientific achievements that have saved countless lives.  If the p value on well chosen, appropriately tests of the delta between a placebo or control cohort and the active study cohort is 0.02, there was a 98% probability that the observed effect occurred because of the intervention and a 2% probability it happened purely by random chance. I don’t understand how you can dismiss this as not being objective.

 

The problem with most amateur DBT is how it’s done, not the principle behind it.

 

of course DBT is a valid and immensely useful scientific method, and

i agree that most amateur DBT are relatively useless.

 

however in most(?) cases at the medical center, i'd guess that you have some (what i'll call) objective output measure such as blood pressure, survival rate, visual acuity, heart ejection fraction........i.e. things you can measure. 

 

compare that with 'the soundstage is wider' or 'it sounds more real' or 'i hear more breath on the vocals'

 

i never meant to imply that DBT is not valid, but that with objective/measurable criteria (versus subjective opinion, even if in large controlled numbers) it is much clearer what is going on.

i assume DBT on psychological research methodology gets a bit messier?

[cat6man]

4 hours ago, bluesman said:

You’re also not that far from Frostbite Falls.  You may even have met some of our audiophile colleagues who studied statistics at Wassamatta U.

 

I'm a big fan of WU! (and still have my coffee mug)

 

This discussion reminds me of situations that happened repeatedly at work over the years.

We'd measure something in the lab and some arrogant PhD would say it was impossible because he had determined that such and such was optimum, blah blah blah.

 

I always insisted that the theoreticians in my department/lab get their hands dirty and verified that their algorithms behaved as expected when implemented.

In my personal experience, I obtained some of my most interesting insights (and patents) from the lab (i.e. real world) experiments not lining up with the oversimplified theories.........like "Why the hell is that happening?".............answer:  the experiment is trying to tell you something dummy!

 

Back to audio:

It really bugs the heck out of me that putting a better power supply on a digital music server can have such a profound impact on my musical enjoyment................I love the enjoyment part but am frustrated that I don't understand the mechanism (actually worse, I don't have a clue!) by which this happens. 

 

I have no specific theory or hypothesis to fit my experience but I think a framework is in sight.  My engineering intuition (or hubris?) suggests that it is related to behavior on the tail of distributions (a phenomenon I've seen repeatedly in my professional work).

A possible framework, though unproven, might look as follows:  (YMMV, ignore the rest if you detest speculation)

 

Whatever mechanism is at work is likely not measurable in an average sense but is likely, IMHO, to be a low probability event.  Let's hypothesize 1% of the time this "something happens".  For red book, this would be ~440 times/sec.  I can certainly imagine that this might be discernible if it affected 440 samples/sec but would yet be unmeasurable on average due to being masked by the other 43,000+ samples.  Occasional long latencies between samples?  Clock jitter spikes?  Short infrequent power supply glitches?  I've no idea but something is going on.

 

[start lecture]

Case in point/analogy:  In wireless communications, using 2 spatially separated antennas give improved immunity to fading and is called space diversity reception, the idea being that if the fading is independent on each antenna the probability that they both are bad (i.e. faded) is greatly reduced.  That's the theory.....and we saw exactly that with a fading simulator in the lab, but not so when testing around a real cell site with space diversity antennas.  WTF?  It turned out that the two antennas have almost independent fading but there was a residual 1-2% correlation in the fading statistics.  On average that would make no difference to the measurements, however the wireless receiver  behaved differently.  Now a 1% correlated signal could be simply modeled as 99% of the time uncorrelated and 1% of the time completely correlated (i.e. both fading at the same time).  The radio receiver was happy as a clam 99% of the time but very unhappy the other 1% of the time, and whenever that 1% of the time occurred the receiver would have to change its operating point and required SNR and the entire receiver loop would have to re-converge.  When we programed the fading simulator to have 1% correlation between the two receiver inputs, we obtained the exact same results as in the outside world.  The 1% correlation did not make any change to the average fading statistics but it had a huge impact on the receiver due to dynamic effects.

[end lecture]

 

So let me put down a friendly challenge.  In the interest of being 'objective' and not 'subjective' in this sub-forum, how about a sub-sub-group interested in getting to the bottom of this technically and not just acting like my old 'arrogant PhD' colleagues who already knew all the answers (but had oversimplified the situation and therefore hadn't formulated the problem accurately)?

 

This will be my last shot at trying to see if anyone else is interested in approaching this in a similar manner to my current way of thinking.  I'm not interested in debating  philosophy of testing and will not reply to such.  Anyone want to try to figure out what is going on here?

 

[cat6man]

19 hours ago, ray-dude said:

 

This is the fun stuff!!  If PhD's are allowed in, count me in!

 

(FYI, I put my hypothesis out there in part 1 of my Extreme review...reference voltage, ground plane, and reference timing are the father/son/holy ghost of digital audio, I think, and everything always seems to come back to those fundamentals)

 

Hell yes, this is the fun stuff (well, that and listening to music).

 

Open-minded folks with a inquiring/scientific bent (PhD or not) are most welcome Ray.

I wonder how much Emile&co measure versus listen when tweaking the Extreme?  If they have found a measurable quantity that is correlated with what we consider 'better' sound, it would be a lot easier to optimize the package or at least get it in the ballpark.  For example, looking at power supply/ground plane spikes and tuning to minimize frequency of events?  Measuring latency variation in delivering samples, mimimizing fragmentation?  I personally would love to experiment with a server where the latencies could be manipulated in a deterministic way (but don't have the programming chops to do so myself).

 

 

 

Too bad I don't have access to a world class lab and test equipment anymore

 

 

 

 

[cat6man]

15 hours ago, fas42 said:

 

Go for it ... 🙂.

 

The overall answer for "what is going on" is that electrical noise from a variety of sources internal and external to the rig impacts the analogue areas of the replay chain; just enough to be audible - this was true 3 decades ago, and is just as true, still, right now. Doesn't matter that the music player is "right over there, way, way from the sensitive stuff!!" ... nasty stuff gets around with the greatest of ease, and your challenge, should you choose to accept it 😝, is to track down and nail every last one of these pathways for the SQ to be degraded by interference mechanisms.

 

The precise, technical explanation for what's going on in a particular setup would be handy to know - but ultimately far less important than knocking the relevant interference pathways on the head ... 😉.

 

i accept!

 

and while the precise technical explanation may be hard to elucidate, why isn't the result measurable at the DAC output?

whatever the exact mechanism may be........

 

is it our inability to measure transient and/or peak distortions at a low enough level?