Popular Post OAudio Posted June 12, 2020 Popular Post Share Posted June 12, 2020 On 6/9/2020 at 6:49 AM, beerandmusic said: audio engineering cannot be that difficult... you are sending A) 5v reference voltage B) digital music (does everybody agree or NOT, that the receiving dac gets this data accurately) C) noise In the past, everyone that spoke up would say that the digital music received is so accurate that it may drop one bit every 24hrs or something along those lines. My thinking, is that if the dac does indeed recieve it's data with near perfect accuracy, and you isolate the 5v reference voltage and "reclock" the "perfect bits" with your own engineering circuit, then it should NOT make any difference how quiet ones pc is or not?? If that is not logical thinking, I just want to know the reasoning. My thinking is that, if that is not logical thinking, then the only thing that would make sense is that A) the bits are not received nearly as perfect as people suggest B) audio engineers still have not figured out a "good design" C) noise is not only not being isolated properly, but it corrupts the music data before input to the conversion circuitry. D) noise is not being isolated properly and it affects the conversion circuitry E) subjective minds inaccurately believe the two systems sound differently. Beerandmusic, this is a very interesting thread. I am relatively new to the forum so its just caught my eye. It's very interesting that asynchronous transfer errors are not resent meaning that it is possible that data can arrive at the DAC uncorrected. I also think that the vanishingly low errors rates that are quoted earlier in the thread may not truly reflect how a real music system's USB interface performs. The low error referenced by the USB standard assumes that transmission conditions meet the USB standards signal eye specifications all of the time. But, consider that successful transmission of music data relies on maintaining USB transmission eye quality on the 480mhz carrier and with differential D+ D- signal amplitude of ~1v. When you look into the logic detection thresholds they are as low as 0.4v and this at 480Mhz down say a 0.5-1.5m USB cable. The transmitting (PC) and receiving (DAC) systems are driven by entirely different power supplies (differential power noise between these two platforms impacts threshold margin, already say just 0.4v, at the receiver). I use USB between PC and DAC with D+ D- USB isolation at the DAC. I also (intentionally) have the ability to match the clock rates between the USB transmission (PC) and USB receiver (DAC). I think the set up of the USB link is pretty good, certainly sound quality is very good but I agree with your list of possible problems (above). So I have taken the step of designing this in line USB board specifically to look at some of the factors in play. If it works as intended it will allow USB signal, power at transmitter / receiver and shield continuity conditions to varied whilst looking for subjective sound quality change. I don't know if this approach is going to generate useful outcomes but faced with so many possible factors, a practical approach might narrow things down. The PCB is produced and on its way to me and I have to populate and test, but fingers crossed that the effort produces useful results. OAudio Currawong and Superdad 2 OAudio Ltd. OAudio Supreme - music server. OAudio RealStream - digital audio components. Link to comment
OAudio Posted June 12, 2020 Share Posted June 12, 2020 24 minutes ago, sandyk said: Just remember that most ultra low noise voltage regulators have a much lower output impedance at >100kHz due to the types and smaller values of filter capacitors normally used. Ideally , the PSU impedance should be as low and flat right across the whole range to 1MHZ as possible. Try also using a much higher value electro in parallel at their output ,perhaps even an Audiophile grade type such as Elna Gold . USB is also sensitive to the capacitance to mains earth in a LInear PSU with an R-Core sounding better than a Toroidal transformer, and with a split bobbin type sounding even better. Even earthing the supplied screen wire of an R-Core transformer can cause a small audible degradation. I verified this by fitting a toggle switch at the rear of a <4uV noise PSU to quickly switch between both. Hi Sandyk, Thanks for the thoughts. My rendering software can't show the second daughter pcb. The second board has a 4uv low noise regulator and option are built in for where it is powered from. I can use this / the PC supply in different combinations for transmitter and receiver bus power. Transformer ground current is a tricky one, its influance is going to show up twice if Im not mistaken from the PC supply and the DAC. Theres quite some thought behind the approach in both these areas but perhaps best to get the board built and tested then go into some more details. sandyk 1 OAudio Ltd. OAudio Supreme - music server. OAudio RealStream - digital audio components. Link to comment
OAudio Posted June 13, 2020 Share Posted June 13, 2020 21 minutes ago, sandyk said: Given that many USB devices, including USB memory, have an internal connection between 0 volts and shield, have you also made provision for switching/isolating the shield lead, as this may result in an inadvertent earth loop . We are on the same page :-) The board is set up to be able to be switched between these options and to examine some ideas to manage transmitter / reciver differential supply noise. I have used this approch in other projects but lots and lots of unknowns with USB transmission so practical testing seems the best way to go. sandyk 1 OAudio Ltd. OAudio Supreme - music server. OAudio RealStream - digital audio components. Link to comment
Popular Post OAudio Posted June 14, 2020 Popular Post Share Posted June 14, 2020 2 hours ago, mocenigo said: Come on, one bit error in 10^12 is waaaaay more than needed. USB has perfect audio transfer provided the sink buffers and reclocks it and the cable has decent shielding (also, the sink should have good galvanic isolation). There is no need for more engineering there. Mocenigo hi, Bit error of 10^12 would do the job for sure...."if" you can get to this performance in a real life implementation. Personally I think there is a lot that needs to be taken care of in PC to DAC system set-up approach this. As I mention above the USB transmission eye detection margin is quite small for the receiver (DAC) at ~ 0.4v. Differential noise between the power supplies of the USB link's transmitter (eg the PC, packed with noisy buck convectors, high transient loads and even an SMPS if your unlucky) and the receiver (the DAC probably on a low noise linear supply) really have the potential to impact eye detection margins. Although the USB cable is shielded, there is also generally a GND loop between the PC and DAC via mains safety earth connections. The PC switching supply noise and ground leakage currents can pollute the safety earth and appear at the USB receiver circuit in the DAC (even though there "should" be a good ground reference established by the USB lead's shield). Then there is EMI coupling into the D+ D- pairs as they traverse the motherboard, if motherboard is used, or from a PCIE card if used. EMI can also be coupled into the USB cable. I have much frustrating experience of "good" quality coaxial cable being insufficiently shielded for low jitter HF signalling. Interesting here is that there are so many reports in forums about improvements in sound from multi shielded USB cables, something I use here too. Final area I think is very important is transmission timing both phase noise and clock speed. The differential noise above may or may not be enough to cause data errors due to eye detection errors. Even if errors are not being caused by detection errors, the differential power noise in the transmitter's & receiver's supplies will cause threshold detection jitter in the USB data stream and this does matter to sound quality (although I would agree this is not data error). I mentioned in my earlier post above I have developed the ability to accurately set the relative frequency of the individual USB clock domains governing the transmitter and receiver. I have been working on this stuff for many years, and know that as little as an 0.000005% difference in the speed of the USB transmitter and receives clock domains can be heard. USB timing really matters if you are aiming for truly high end sound quality. The point of the diagrams below is not to highlight that using a 3 or 5m cable could be a bad move (most people just don't go that long for audio :-) ), rather my point is something as simple as the cable length alone can really degrade the eye detection margins. The issues listed above I think have far greater potential to harm eye margin performance than these example cable lengths. sample USB transmission eye 9 inch cable eye 3m cable eye 5m cable I don't have USB test equipment (way too expensive) but I have been modifying USB interfaces and audio servers at board level for > 14 years. I just can't say beyond doubt that the above issues cause actual errors but I have come across lots of evidence that the areas above really matter for quality. I happened to be working up that board I posted about above prior to seeing this thread.I though it would be fun to post about this. It is able to do much more than condition power and make or break shield links etc. I felt its worth the time to see if anything useful can be pinned down. Best regards, OAudio. Currawong, sandyk and fas42 1 2 OAudio Ltd. OAudio Supreme - music server. OAudio RealStream - digital audio components. Link to comment
OAudio Posted June 15, 2020 Share Posted June 15, 2020 1 hour ago, beerandmusic said: may be of interest:::: https://news.ycombinator.com/item?id=7065091 Thanks its a very interesting read, Timing, Signal integrity (inc transmission, detection and cable effects), PSU influence, Onward processing, and USB transfer & error handling, all hotly debated :-). I think the excellent white papers @Superdadlinked above pull these into a broad and cohesive picture. OAudio OAudio Ltd. OAudio Supreme - music server. OAudio RealStream - digital audio components. Link to comment
OAudio Posted June 15, 2020 Share Posted June 15, 2020 22 hours ago, Superdad said: With all due respect--and a warm welcome to the Audiophile Style forum--the issues you discuss above are being addressed by some. UpTone pioneered (back in 2014) USB signal integrity improvement for audio (using a hub chip, improved clocking, and attention to PS and impedance) with our original USB REGEN. And then we leap-frogged ourselves--and those who had followed us--with the more advanced ISO REGEN in 2017. Galvanic isolation, ultra-low-phase-noise clocking, and a pile of LT3042 regulators. Measurable improvements in SI: Without ISO REGEN: With ISO REGEN: We also put forth a couple of papers on the subjects: https://cdn.shopify.com/s/files/1/0660/6121/files/UpTone_REGEN_tech_summary.pdf (regarding the original USB REGEN) and https://cdn.shopify.com/s/files/1/0660/6121/files/UpTone-J.Swenson_EtherREGEN_white_paper.pdf?v=1583429386 (related primarily to our EtherREGEN switch but also applicable with regards to the effects of clock threshold jitter with USB as well). Hi Alex, Thank you for the warm welcome . I know you are already on your second iteration of a solution for USB transmission with the ISORegen, I love the concept. I read the white papers when they were published and thought they were brilliant at the time. They are a great compendium and analysis of influences on USB sound. It's refreshing to see such valuable information coming out in papers. I'v heard the ISORegen once, unfortunately at a show in a system components I had not heard before. It was very good but I'm looking forwards an opportunity for a longer listen at some point. I actually owned a Silanna + PHY hub design but not as meticulously designed and implanted as the ISORegen (actually I bought the unit because I needed to source an ICE08USB chip for some repair work !). If I explain the general approach I am pursuing for USB in my system, it might help understand the scope of the SI testing I am doing. Experience over time has lead me down the route of doing what I can to keep the USB data's journey from PC (CPU) to DAC as simple as possible. This has meant a lot of work in the audio server to ensure good USB timing and power (clocks and PSUs are to my own designs). The work has helped promote a well timed USB stream and good USB SI from the server. I should mention that at the server's USB is handled by its PCH chip as this is not that common an approach any more for very high quality sound. Indeed its a break for me after years of testing and screening different USB chipsets and working on boards etc, but my server's motherboard was carefully researched and modified and the sound its providing now is remarkably real. The one exception to this simple approach is USB isolation. Like many I also think this is nowadays a necessity. Of a few isolation solutions I tried, by far my favourite for sound quality have been the Silanna ICE08USB designs (I know this wont be a surprise). Happily the DAC I have has this on its USB input as a standard feature. The Silanna then feeds directly into the DACs internal USB interface without further processing. So just two clock domains the servers USB clock and the DACs PHY clock. There's a lot of lower level detail in and behind the but essentially the above is the set up I am working with. The point that sparked spinning up of the test board was this: Of two identical good USB cables, one 1m the other 0.5m, the shorter is clearly better to listen to (not a revelation maybe others have found this too). There are lots of possible reasons but having already played around with the ICE08USB a little and after this experience with the shorter cable (better SI ?), I want to practically see if there are any sound quality upsides available from improving signal at the ICE08USB inputs. The board I have spun follows my keep it simple approach. Its not a PHY Hub design like the ISORegen which works for me as there is no packet processing or most importantly for me added clock domain that will interact with the clocking design I have in my server. The board design is analogue and should achieve extremely low transmission latency. I am keen for it to be as transparent as possible so the server remains the main influence on the data stream. So not that similar to the ISORegen other than the SI conditioning you seem to be achieving with the PHY Hub's output. I happened to be sending some stuff off for fab and though it might be fun to spin a board to try this. Of course if your going to make the effort its sensible to build in flexibility to play with power options and shield setups which is know is well trodden but still important. 22 hours ago, Superdad said: One question for you: Are you affiliated with a company in audio? You took the member name OAudio, write knowledgeably, and are doing PCB layout, hence my wondering. I don't have affiliations but do have a [very] strong desire not to listen to digital distortions in music. I'm quite happy to get stuck in and develop and build stuff if I think its going to help achieve this. My background was research scientist then software, IT / Telecoms. I ran a global solutions business supporting System Integrators until recently. I am on sabbatical just now which means I possibly have a bit too much time to peruse audio . Cheers, Nick. Currawong 1 OAudio Ltd. OAudio Supreme - music server. OAudio RealStream - digital audio components. Link to comment
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