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USB audio transmission isn’t bit true


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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.

 

 

OAudio Ltd.

OAudio Supreme - music server.

OAudio RealStream - digital audio components.

 

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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.

 

 

OAudio Ltd.

OAudio Supreme - music server.

OAudio RealStream - digital audio components.

 

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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.

 

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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:

591f368a10ad6_LenovoUSBporteyepattern.thumb.jpg.4ecc2ae79b185340944fe829f16ac17a.jpg

 

With ISO REGEN:

591f36885ae04_ISOREGENeyepattern.thumb.jpg.8dde1242868ff79ab6067d8fa6418224.jpg

 

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.

OAudio Ltd.

OAudio Supreme - music server.

OAudio RealStream - digital audio components.

 

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