ray-dude Posted June 18, 2020 Share Posted June 18, 2020 Thank's for the pointer to this topic Ken. My hypothesis is that switching to the laser is causing a correlated pulsing on the reference voltage and/or ground planes that is having an indirect impact on the DAC. My basis for this is that in previous experiments with coax SPDIF signals to my Chord DAVE, that particular DAC seemed to have a strong susceptibility to parasitic signals in the 2-3GHz band. Copious ferrites on the dual coax connectors to the DAC had a surprising benefit to SQ. IIRC Rob Watts (designer of the DAC) attributed the impact to noise floor modulation in the DAC (I would have look up some old notes to confirm). It is easy to replicate this by having a WiFi basestation configured for 2.4Ghz and bringing it close to this DAC, or having music server on WiFi that is close to the DAC. All above is hypothesis or experiential. kennyb123 1 ATT Fiber -> EdgeRouter X SFP -> Taiko Audio Extreme -> Vinnie Rossi L2i-SE w/ Level 2 DAC -> Voxativ 9.87 speakers w/ 4D drivers Link to comment
Popular Post ray-dude Posted June 18, 2020 Popular Post Share Posted June 18, 2020 8 minutes ago, plissken said: You want to know what would really get laughs at an engineering school? You're ability to hear differences between SFP+ modules. FWIW, at the engineering schools I went to the reaction would have been "No way! Let me hear that... Huh... Wow... What the hell is going on? Cool, let's try to figure this out!" This is the exciting stuff! I hope that is the spirit of this thread. Alas, I have very limited access to measurement equipment right now, so I'm limited to offering (somewhat) informed hypotheses and experiences, and feedback on any experiments or interpretation of results that folks do. Wish I could do more, since given what I'm hearing, this is a pretty compelling topic for me. MarkS, kennyb123, The Computer Audiophile and 1 other 1 3 ATT Fiber -> EdgeRouter X SFP -> Taiko Audio Extreme -> Vinnie Rossi L2i-SE w/ Level 2 DAC -> Voxativ 9.87 speakers w/ 4D drivers Link to comment
ray-dude Posted June 18, 2020 Share Posted June 18, 2020 Paul, I have a couple different components that are SFP capable: The StarTech PEX1000SFP2 PCIe optical Network card in my Taiko Audio Extreme (2x) Ubiquiti EdgeRouter X SFP's Sonore opticalModule I recently sold my Uptone Audio EtherREGEN, but I was experimenting with the SFP port on the ER in my Taiko Audio SGM Extreme review (part 4 for those subjective findings) I currently have some TP Link multi-mode SFPs connecting my two EdgeRouter X SFPs. ERX1 is my router/gateway and connected to my ATT fiber ONT. It has a audio subnet that I connect by copper to my opticalModule. I run fiber from the opticalModule to my Extreme. I've run both the Planet Tech SFPs and Finisar SFPs on my audio net. I have the rest of my home network (including WiFi) on ERX2, galvanically isolated from ERX1. ERX2 is configured as a simple switch, but I do have a couple VLANs for my WiFI (guest network, IoT network, etc) With the Planet Tech SFPs, I preferred copper NIC on the Extreme (fiber to the opticalModule+PlanetTech to copper to the Extreme). With the Finisars, I'm back to preferring the optical NIC, esp. now that I have my audio network isolated from my home network, but it isn't a clear preference. FWIW, subjectively, reduced network traffic to the my music server NIC does have an impact. This is contributing to my hypothesis of laser switching-induced electrical noise being the mechanism in play. All of the above is with streaming TIDAL content to Roon to HQP to DAC. The network part of my system is very much in flux right now, because of what I've been hearing. There are a couple of permutations I'd like to try to see if it helps develop a hypothesis for a what a core mechanism could be. Here is my wish list for things to try if I had proper equipment in quarantine with me: * Probe power rails on the SFP modules and look at spectrum of noise generated on same by network traffic. If that spectrum is the same, my hypothesis can filed in the "oh well" cabinet. If different, then the question shifts to whether that difference is audible (and if so, how). * Build an extender and wire to SFP cage outside of NIC/FMC/Routers/etc. Rig so that I can swap between powering SFP externally or via the cage leads. If there is variability with different class power supplies, that would generally support the laser-switching-noise hypothesis. If not, back to the "oh well" cabinet we go. * Get access to OEM data sheets for SFP modules and find the lowest power consuming unit available...give it a listen, get another subjective data point @Superdad without asking you to divulge anything proprietary, did you or John look into any of these things when you were designing and prototyping the ER? (and if that is poking at things that you consider proprietary, my apologies in advance) ATT Fiber -> EdgeRouter X SFP -> Taiko Audio Extreme -> Vinnie Rossi L2i-SE w/ Level 2 DAC -> Voxativ 9.87 speakers w/ 4D drivers Link to comment
ray-dude Posted June 19, 2020 Share Posted June 19, 2020 6 minutes ago, Superdad said: P.S. By the way, @plissken's first name is Mark not Paul. (And over at ASR he is Jinjuku; various other names elsewhere...) Mark, my apologies! I have no idea how "Paul" settled into my brain, but certainly no disrespect was intended. Thank you Alex for the gentle correction (as well as the info that you shared) ATT Fiber -> EdgeRouter X SFP -> Taiko Audio Extreme -> Vinnie Rossi L2i-SE w/ Level 2 DAC -> Voxativ 9.87 speakers w/ 4D drivers Link to comment
Popular Post ray-dude Posted June 26, 2020 Popular Post Share Posted June 26, 2020 A detour, then back to OT I've done a lot of user experience testing over the years (a LOT). I've also been heavily involved in more formal scientific testing (drug clinical trials, etc). The former seems more germane to our humble hobby, but that's neither here nor there. What I found with user experience testing is that the best insights and outcomes didn't come from asking people which they preferred, but from watching them think about it, then designing for that insight. User experience testing that focused on direct measurement ("Do you prefer the menu on the left or the right?") would more often than not lead us astray because we were misinterpreting what we were measuring. For example, most of us are of an age where we remember the Pepsi challenge. People would try blinded Pepsi vs blinded Coke, and people would prefer Pepsi. Pepsi is better than Coke, right? Heck, let's make it double blind by having the person handing out the samples in white papercups not know which is which. That will make us even more scientific. If you prefer Coke, you're wrong! The problem is that that test was measure first use preference, not long term use preference. Pepsi had (has) a stronger sugar slam, but it lacks depth and subtle over time. Based on first use, Pepsi wins more often than their market share. However, purchasing preference and people trying Pepsi but going back to Coke indicates that based on long term use, Coke wins over Pepsi for most people. This paralleled my experience with user experience testing, where most testing results were interesting but irrelevant because we were measuring first use preference. You really had to observe long term behavior to infer proper preference, and even then, more often than not, the value was getting an insight that then fed into the next design iteration. Back to audio. Same pattern gives us dynamic range compression. First listen sounds better when things are "louder". Over time, it is an ick of an experience for a lot of us. Loudness wars mastering is Pepsi, high dynamic range masterings are Coke. Some people prefer Pepsi, I prefer Coke. I guarantee that if you were to do extended DBT testing of low DR masterings vs high DR masterings and ask what people prefer, a huge majority would prefer the low DR mastering based on first listen (yes you could carefully volume match, etc, but I'm offering this as an example, not as an experimental design). I bring this up on this thread, because SFPs are falling into that same pattern for me. This is a class of component where I'm finding I have to ignore my initial experience and preference, and gauge my mood after extended listening. Do I want to listen to music longer? Am I able to focus on work more or less when listening to music with a particular SFP pair? Like my user experience example above, once I identify a long term preference, I then look for what short term identifyable characteristic is a "tell" for what that long term experience will be, then look for components that have more or less of that tell. I'm starting to find that "tell", but I still have to lean into extended listening Audiophile Neuroscience, kennyb123 and motberg 3 ATT Fiber -> EdgeRouter X SFP -> Taiko Audio Extreme -> Vinnie Rossi L2i-SE w/ Level 2 DAC -> Voxativ 9.87 speakers w/ 4D drivers Link to comment
ray-dude Posted June 26, 2020 Share Posted June 26, 2020 1 hour ago, cat6man said: 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 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) ATT Fiber -> EdgeRouter X SFP -> Taiko Audio Extreme -> Vinnie Rossi L2i-SE w/ Level 2 DAC -> Voxativ 9.87 speakers w/ 4D drivers Link to comment
ray-dude Posted June 29, 2020 Share Posted June 29, 2020 I remember looking at this page when I first heard differences. On pins 15 and 16, the laser is actually turning on and off (even if fed with a differential signal). Unless the power is getting dumped into an offsetting load when laser is off, that will create a correlated pulsing load on the power lines, no? My (very) naive assumption was that the power driver circuit biases the laser to the critical voltage, and the differential signal switches it on and off. All that being said, I'm obviously not familiar with how the driver circuits in these modules are typically implemented nor the compliance requirements for noise on ground plane or power plane, so above is an honest question, not a belligerent one (I'm honestly delighted to toss wrong hypotheses on the "Oh Well" pile...life's too short to chase dead ends) Audiophile Neuroscience 1 ATT Fiber -> EdgeRouter X SFP -> Taiko Audio Extreme -> Vinnie Rossi L2i-SE w/ Level 2 DAC -> Voxativ 9.87 speakers w/ 4D drivers Link to comment
ray-dude Posted June 30, 2020 Share Posted June 30, 2020 The presumption I've been working with is that signal integrity is effectively a given with these devices, which is why I've been paying more attention to possible impact on power/ground planes (other candidate is radiated RF, but that seems a stretch as well) I most certainly was not expecting to hear differences between SFPs (pretty stunning actually, for all the reasons you cite, as is anything on the network having an impact on SQ) I should give the caveat that my only experience has been wth 1 gigabit SFPs. Do you (or others) happen to know the type of laser typically used in these devices? At a $20-30 price target, I was presuming these low cost modules wouldn't be using more advanced photonics (I'm a geezer...it's been almost 30 years since I've done work on DFB lasers, and back then, we were delighted just to get them to work). I spent a little bit of time looking for a published reference design for a 1G SFP module, but didn't (yet) find anything current. What I did find had a simple driver on the LED laser module, with the differential signal switching the laser on and off: https://www.analog.com/media/en/reference-design-documentation/reference-designs/5693022520349015544867851905SFP_RDK_pra.pdf If someone has a pointer to a more modern published reference design for a 1G SFP module (with presumably more advanced photonics than an LED laser), it would be very helpful to understanding what is going on inside of these beasts. If 10G modules have more advanced photonics switching, that could be an argument for making the investment in 10G network gear (I have not had access to this sort of kit to test, although it is definitely on the list). ATT Fiber -> EdgeRouter X SFP -> Taiko Audio Extreme -> Vinnie Rossi L2i-SE w/ Level 2 DAC -> Voxativ 9.87 speakers w/ 4D drivers Link to comment
ray-dude Posted June 30, 2020 Share Posted June 30, 2020 47 minutes ago, jabbr said: This has a list of SFP/SFP(+) and QSFP(+) modules with the type of laser in https://www.finisar.com/sites/default/files/resources/finisar_optical_transceiver_product_guide_3_2015_web.pdf As you can see the SFP multimode modules tend to be VCSEL and the single mode modules tend to be DFB ... as of 2015 Fantastic, thank you! My (currently) preferred FTLF1324P2BTL is a Fabry-Perot laser, which seems to be operated like a laser diode? (direct modulation, limited to lower bandwidth channels) Alas, I'm not finding more modern reference designs (yet), but the older ones I've found all have Vcc direct to the laser diode or driver in the block diagrams. If the 10G modules have a constant power load to go with their tighter operating tolerances, that certainly makes them even more interesting. ATT Fiber -> EdgeRouter X SFP -> Taiko Audio Extreme -> Vinnie Rossi L2i-SE w/ Level 2 DAC -> Voxativ 9.87 speakers w/ 4D drivers Link to comment
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