USB audio transmission isn’t bit true

[Superdad]

9 minutes ago, OAudio said:

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).

Indeed.

 

9 minutes ago, OAudio said:

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.

So nice to read people who get this!

 

9 minutes ago, OAudio said:

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. 

 

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).

 

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.

 

Cheers,

--Alex C.

[sandyk]

34 minutes ago, OAudio said:

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.  

 I am able to demonstrate that a trip through a generic 3MJ long USB memory stick causes audible degradation, and it is even more obvious with 2 trips through this cable, yet the Data is still error free

[sandyk]

4 hours ago, sandyk said:

 I am able to demonstrate that a trip through a generic 3MJ long USB memory stick causes audible degradation, and it is even more obvious with 2 trips through this cable, yet the Data is still error free

In reply to OAudio

OOPS!

 Trying to do 2 things at the same time.

 I am able to demonstrate that a trip through a generic 3M long USB cable to a USB memory stick causes audible degradation, and it is even more obvious with 2 trips through this cable, yet the Data is still error free.

 Attached is the far more simplistic test set up than yours that I am using, where it is also easy to play around in the Capacitance Multiplier section of the modified John Linsley Hood designed PSU Add On (A.K.A. " Ripple Eater") with different types of Electrolytic capacitors.

It currently has a low value resistor inserted in the 0 volts line, and a simulated capacitance of around 2 FARAD.

 It also functions with the +5V from the PC disconnected at the PC end of the cable .

[mocenigo]

8 hours ago, sandyk said:

 I am able to demonstrate that a trip through a generic 3MJ long USB memory stick causes audible degradation, and it is even more obvious with 2 trips through this cable, yet the Data is still error free

 

Ok, but then you conclude that the USB transmission is not bit perfect? I would say, it is the USB reception (I do not scientifically claim this is the only problem, but it is far more likely). In other words, there are voltage drops in the signal that cause read uncertainty. And this can be remedied. These are very old and very well known problems, for instance, in ethernet connections and in professional audio, where there are repeaters the read the signal before it get too weak, and regenerate it. Nothing new. And this is known to cause read errors if the cables are too long/have too high a resistance.

 

Then use very short cables or a good regenerator near the sink.

[sandyk]

20 minutes ago, mocenigo said:

Ok, but then you conclude that the USB transmission is not bit perfect?

 

No, I am NOT saying that. Neither are the numerous members in Rajiv's massive thread in Music Servers.

[mocenigo]

Just now, sandyk said:

 

No, I am NOT saying that. Neither are the numerous members in Rajiv's massive thread in Music Servers.

 

Perfect, then 🙂

[sandyk]

8 minutes ago, mocenigo said:

 

Perfect, then 🙂

 

Do you REALLY believe that the many different USB cables that members report as sounding different, are all due to Data errors ?

[mocenigo]

4 minutes ago, sandyk said:

 

Do you REALLY believe that the many different USB cables that many members report as sounding different, are all because of Data errors ?

 

There may be a Data error because of the reception. Since the mode is isochronous, if there is no delay the data is read correctly and also timed correctly, provided the sink's USB interface can issue the bits without jitter to the I2S interface.

 

What can happen us that the effort to read weak data can induce annoying voltage or current variations in the US interface's circuitry or its supply, which then propagates as noise. Which adds to the noise possibly captured and injected in the system via the USB connection itself. Therefore, with a bad USB interface, cables can induce (I would refrain to use "make") a difference.

 

If there is more, I am willing to know and learn it.

[mocenigo]

10 hours ago, OAudio said:

 

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.

       

 

Hi, yes I was expressing myself in a incorrect way.  Length of course has a role and that 1/10^12 is in ideal conditions (maybe 1 meter?) but I indeed mentioned repeaters and regenerators.  A problem well known in the industry even before the audio folks noticed, the error rate at the sink's interface, i.e. the eye detection. 

[sandyk]

38 minutes ago, mocenigo said:

 

There may be a Data error because of the reception. Since the mode is isochronous, if there is no delay the data is read correctly and also timed correctly, provided the sink's USB interface can issue the bits without jitter to the I2S interface.

 

What can happen us that the effort to read weak data can induce annoying voltage or current variations in the US interface's circuitry or its supply, which then propagates as noise. Which adds to the noise possibly captured and injected in the system via the USB connection itself. Therefore, with a bad USB interface, cables can induce (I would refrain to use "make") a difference.

 

If there is more, I am willing to know and learn it.

I have previously mentioned noisy or poor waveforms resulting in timing variations and Jitter.

It still doesn't explain how some attribute a particular sound quality to some cables, e.g.warmth or Analogue sounding, not just like a veil being removed or less harsh sounding.

[mocenigo]

Just now, sandyk said:

I have previously mentioned noisy or poor waveforms resulting in timing variations and Jitter.

It still doesn't explain how some attribute a particular sound quality to some cables, e.g.warmth or Analogue sounding, not just like a veil being removed or less harsh sounding.

 

Well, per se I cannot fathom how a Digital cable might be "warm".

 

But we can try to guess how this may be a consequence: a good amount of errors and jitter will have a larger effect on higher frequencies (disrupting their reproduction, potentially smearing them) and therefore will result in less highs, and therefore increased relative presence of mids and bass. So: "warmth" (but one could also hypothesise that these errors could add "sparkle"). Perhaps also more "analog sounding" (rolled off treble and thus more resembling vinyl).

 

But this would also vastly depend on the sink's interface.

 

 

[beerandmusic]

10 hours ago, Superdad said:

 

 

On 6/12/2020 at 3:19 PM, OAudio said:

 

 

may be of interest::::

 

https://news.ycombinator.com/item?id=7065091

[OAudio]

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

 

 

 

[barrows]

As an addition to this discussion, I would add what I think the Lush USB cable "does" to make it sound different.  PeterSt. has kind of hinted at this, but has never directly admitted it to my knowledge.  PeterSt does admit that the Lush USB does not conform to the USB impedance specifications, purposefully.  He seems to claim the cable is slower: ie what we would call poor signal integrity, with more slope in its rise and fall.  What he appears to be saying that this does is that the slower transition edges hit the receiver more "softly", and then he suggests (again, I am reading a bit between the lines of what he says, PeterSt is often a bit obtuse, perhaps on purpose to not give away his "secrets") that this softer hit, gives rise to less RF/noise generation in the receiver.  I am not aware if anyone has ever actually measured this, it should be measurable by an RF lab at the very least.

 

I can say that the Lush (my experience was with the original version) does exhibit a "softer" "warmer" , even a bit "fuzzy" presentation from a subjective perspective (it was not for me in my system).

I would say that how the USB "system" interacts is going to matter, as is true for most signal transmission "systems"

 

For me, given a good USB source (dedicated, not a commercial computer which is multi tasking while playing music, and no shared devices on the USB bus) and good USB receiver in the DAC, I am certain that data errors are not an issue for sound quality.

 

For me, that leaves only the various forms of noise.  Including noise generated by the receiving device.  The noise on the receiving chip may change with signal integrity, and power supply impedance/noise.

 

I have always found good isolation of the USB receiver section in a DAC to help matters, but we must understand that such isolation s not a panacea: it helps, but cannot fix all issues.  This is likely because some noise can capacitively couple across a 4 mm "moat" on a PCB.  Such isolation requires that the DAC re-clock the I2S lines before conversion, hopefully via a masterclock and flip flop located very close to the final conversion stage.  Of course an isolated USB receiver needs a dedicated power supply, this can be provided very well by the USB 5 VDC supply, if one is sure their USB source has a clean/low impedance 5 VDC supply, and that the USB cable keeps this supply clean/low impedance.  For the USB power supply in the source, as an example, Sonore opticalRendu pays specific attention to the quality of the USB 5 VDC supply, with a dedicated LT 3045 regulator a few mms from the USB output.  One can also use devices like the IsoRegen to inject a clean 5 VDC supply.  Good layout inside the DAC in terms of airborne RF interference from the USB receiver is a good idea as well and perhaps some shielding/damping as well.   There are certainly well engineered DACs available which pay attention to all of these details.

[beerandmusic]

6 hours ago, OAudio said:

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

 

I never saw your response to superdad about your profession and am curious myself?

[beerandmusic]

3 hours ago, barrows said:

  There are certainly well engineered DACs available which pay attention to all of these details.

 

What is lowest price DAC that you are aware of that does "pay attention to all of these details"?

[OAudio]

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.

[barrows]

3 hours ago, beerandmusic said:

 

What is lowest price DAC that you are aware of that does "pay attention to all of these details"?

 i have no idea, I have not examined all DACs on the market!  Typically, it is more expensive to incorporate good isolation, i have not seen such in low price DACs (like Topping, etc).

You have ask manufacturers about this yourself if your shipping for DACs if they do not specify how their USB input is implemented.

[beerandmusic]

1 hour ago, barrows said:

 i have no idea, I have not examined all DACs on the market!  Typically, it is more expensive to incorporate good isolation, i have not seen such in low price DACs (like Topping, etc).

You have ask manufacturers about this yourself if your shipping for DACs if they do not specify how their USB input is implemented.

you stated there are many dacs that do this...i wasn't asking which are inexpensive...i just asked of the dacs that you are aware of, which is the least expensive one that you are familiar with?

I believe the schiit dacs do this with their "unison" usb, but Miska said the bifrost didn't measure well, so am looking at other options, and would prefer DSD if possible, but not necessary.

Even of the "many" you suggest, none are inexpensive, I still want to know which is the least expensive one you are familiar with as a "starting point"

[beerandmusic]

1 hour ago, OAudio said:

 

 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 don't know if I understood another person correctly or not, but I thought I understood them to say that almost all DACs use their own clock in modern day dacs, so why would the pc source clocks matter regarding timing?

[barrows]

34 minutes ago, beerandmusic said:

you stated there are many dacs that do this...i wasn't asking which are inexpensive...i just asked of the dacs that you are aware of, which is the least expensive one that you are familiar with?

I believe the schiit dacs do this with their "unison" usb, but Miska said the bifrost didn't measure well, so am looking at other options, and would prefer DSD if possible, but not necessary.

Even of the "many" you suggest, none are inexpensive, I still want to know which is the least expensive one you are familiar with as a "starting point"

The current version of the Holo Audio Spring I guess counts as a relatively inexpensive DAC, with a good, isolated, USB interface.  Like i said, i am not aware or every dAC available, and the technical details of all.  So to be fair to DAC manufacturers I really do not want to make a list.

Anyway, if you are shopping for DACs, perhaps you could do some of your own research on this instead just asking for other's to do it for you.  Ultimately, to decide on any DAC purchase, a listening test at home in your system is the only way to go, as not everyone is gong to agree on which s "best' and different system contexts matter as well.

[beerandmusic]

2 hours ago, barrows said:

The current version of the Holo Audio Spring I guess counts as a relatively inexpensive DAC, with a good, isolated, USB interface.

 

Thanks for sharing..this is the type of information i am looking for.

 

In your statement:: Such isolation requires that the DAC re-clock the I2S lines before conversion, hopefully via a masterclock and flip flop located very close to the final conversion stage.  Of course an isolated USB receiver needs a dedicated power supply, this can be provided very well by the USB 5 VDC supply, if one is sure their USB source has a clean/low impedance 5 VDC supply, and that the USB cable keeps this supply clean/low impedance.  

-----------------------------------

Can you clarify. 

1.  Does the Holo re-clock in the manner which you suggest above?

2. Does the holo provide it's own 5v or does it use the usb 5v? 

 

[Superdad]

22 minutes ago, beerandmusic said:

Can you clarify. 

1.  Does the Holo re-clock in the manner which you suggest above?

2. Does the holo provide it's own 5v or does it use the usb 5v? 

 

Please see my long-ish reply here:

 

Honestly, I think the discussion of DAC clocking (and feeding back of master clock across digital isolation moat to USB board--what Barrows is taking about) is only going to confuse you and is not terribly relevant to your search for a DAC. Understanding this stuff is hard enough for those non-engineers (like myself) who are steeped in it (I consider myself lucky to be very "engineer-adjacent" via my close relation with John Swenson). I think it is going to be difficult for you to choose based on informal discussion of many technical factors. 

[beerandmusic]

3 hours ago, Superdad said:

Understanding this stuff is hard enough for those non-engineers (like myself) who are steeped in it (I consider myself lucky to be very "engineer-adjacent" via my close relation with John Swenson). I think it is going to be difficult for you to choose based on informal discussion of many technical factors. 

 

That may be true, but how is it possible for anyone to make a decision then on which ones to try?

They can't base it solely on measurements, and they can't base it on debatable technologies.

THat is the problem with the hobby.  Sure you can say base it on your own hearing...I have already tried that as well trying a multitude of them.  No one can seem to offer "logical" reasoning for the layman.  By definition of function of the dac, all dacs should sound exactly the same, and I have yet to find one usb dac that sounds as good as other interfaces.  I am very close to giving up on the endeavor again to find a usb dac that sounds any better than playing from a smart phone or streaming through a cheap avr...  Even the objectivists on the "other site" suggest that all dacs with good measurements will sound the same...so that I guess is where this will end...i guess I just had higher hopes.  I know davide256 suggest the mojo is the answer, where one person over there (that is presumably well respected there), has the mojo and suggests it sounds exactly the same as any other dac that isn't "trash".  Then when you question people (whether they believe all dacs sound the same or you have to have the best pc, the best power supply, the best isolation, and even then it won't be good enough), they belittle you and just say "just believe us", even though they are on totally different belief systems.    One side suggests spend whatever you want they will all sound the same, and the other side suggests you have to spend a fortune, and there are so many improvements....I personally believe that it has to be somewhere in between the two extremes, so I have to use something to guide me....sure i can just buy another 15 dacs and resell them again, and let my own ears decide....and i will probably still be of the same mindset after all that effort, that all these improvements haven't really amounted to anything and that streaming DSD through my marantz still sounds better....and that's not necessarily a bad thing...it actually sounds pretty damn good....i just would prefer to have it sound this good through usb....yawn.

[beerandmusic]

4 hours ago, Superdad said:

 

Anyway, i liked your first response better, that i believe, if i understand correctly, is that all dacs "regenerate" (term used loosely) to indicate it goes through some processor, and no dac literally isolates the usb 5v reference....so we are back at square one...do dacs compensate for usb noise sufficiently or not....one side will say they do and that usb noise cannot make a difference and they will all sound the same, and the other side will say you have to spend a lot of money and they still will not compensate enough.......which is why i would like a dac that does isolate as best as possible since it is "debatable" that audio engineers cannot agree on.

 

That said, i guess, I can simplify my desires in my next usb dac to just be galvanically isolated that measures well and I can skip the part about having it's own 5v reference voltage or one that reclocks....not sure there would be anything else to look for in making a decision.