USB audio cracked... finally!

[mmerrill99]

7 minutes ago, scan80269 said:

Good (or bad) implementation can easily make a larger difference than the type of transport interface.

Agreed & it appears that once certain issues are adequately addressed in USB audio, it can be one of the best sounding audio interfaces.

[pkane2001]

3 hours ago, scan80269 said:

USB as a transport for digital audio (from computer/streamer source to DAC) differs from other digital audio transports like I2S, S/PDIF coax & Toslink optical, AES, etc. in that with USB, there is no audio timing whatsoever in the data packets running over the cable.  Every DAC that has a USB input must re-clock the digital audio stream received over USB into an audio clock domain of a power-of-2 multiple of either 44.1KHz or 48KHz depending on the sampling rate of the audio stream being transported.  

 

That's right. And that's why I asked the question. If the timing of the actual audio samples is driven by an on-board clock, how does the timing error in the USB packets affect this clock? How does the error in timing due to a poor 'eye pattern' or HF rolloff of the square wave edges result in anything audible after the samples are collected in a FIFO buffer and then doled out using the onboard clock? This question is important in explaining how a USB cable might or might not affect the analog domain.

 

Of course, if timing errors and square wave distortions are not the issue, and instead leaked noise from the PC side is the problem, then perhaps a better isolation between the PC and the USB receiver would eliminate the need for fancy cables. 

 

[mmerrill99]

28 minutes ago, pkane2001 said:

That's right. And that's why I asked the question. If the timing of the actual audio samples is driven by an on-board clock, how does the timing error in the USB packets affect this clock? How does the error in timing due to a poor 'eye pattern' or HF rolloff of the square wave edges result in anything audible after the samples are collected in a FIFO buffer and then doled out using the onboard clock? This question is important in explaining how a USB cable might or might not affect the analog domain.

Your question suggests that a FIFO buffer & onboard clock are ideal, isolated functions not influenced by any noise which may be happening within the USB audio device as a result of signal integrity issues at the USB receiver stage. This is unlikely to be the case & could be a possible way that SI issues become internal noise issues within the system

28 minutes ago, pkane2001 said:

Of course, if timing errors and square wave distortions are not the issue, and instead leaked noise from the PC side is the problem, then perhaps a better isolation between the PC and the USB receiver would eliminate the need for fancy cables. 

It may also be a noise issue & cables can also be responsible for different noise profiles

[pkane2001]

9 minutes ago, mmerrill99 said:

Your question suggests that a FIFO buffer & onboard clock are ideal, isolated functions not influenced by any noise which may be happening within the USB audio device as a result of signal integrity issues at the USB receiver stage. This is unlikely to be the case & could be a possible way that SI issues become internal noise issues within the system

It may also be a noise issue & cables can also be responsible for different noise profiles

 

So, are you saying that USB cables improve SQ by reducing noise in the digital transmission?

 

Seems to me that a USB cable is not the best way deal with noise, and that there are much better ways to stop it from entering DAC. Galvanic isolation being one of the obvious ones. 

[scan80269]

29 minutes ago, pkane2001 said:

 

That's right. And that's why I asked the question. If the timing of the actual audio samples is driven by an on-board clock, how does the timing error in the USB packets affect this clock? How does the error in timing due to a poor 'eye pattern' or HF rolloff of the square wave edges result in anything audible after the samples are collected in a FIFO buffer and then doled out using the onboard clock? This question is important in explaining how a USB cable might or might not affect the analog domain.

 

Of course, if timing errors and square wave distortions are not the issue, and instead leaked noise from the PC side is the problem, then perhaps a better isolation between the PC and the USB receiver would eliminate the need for fancy cables. 

 

I'm going to take a swag at answering your questions, though I humbly profess that I'm far from being a "know-it-all"...

 

In theory, signal integrity of USB signals entering the USB front-end of a DAC should have no effect on the digital-to-analog conversion and downstream analog output circuitry.  In reality, the quality of the USB signals arriving at the DAC USB receiver will greatly affect how hard the USB interface chip (e.g. XMOS) has to work to retrieve the bitstream.  The more active a block of digital (or digital/analog hybrid) logic works, the more power hungry it becomes so it dumps more electrical noise onto the power & ground planes it sits on.  Unless very well isolated, this electrical noise can make its way to the D-to-A conversion circuitry and induce increased jitter into the conversion, which can then be heard as degraded sound at the analog outputs.  John Swenson has explained this phenomenon in great detail.

 

A good USB re-clocker should greatly reduce the audible impact of the USB cable, though as John may have also indicated, the key word is reduce, not eliminate.  With increasing evidence that the USB data signals (D+ & D-) can carry noise in addition to the intended USB signal, coupled with USB receiver PHY's ability to attenuate common-mode noise but not differential mode noise, we probably have a scenario of some amount of noise (mostly differential) getting through to the clock and data recovery logic sections, thus inducing more activity and noise.

 

Galvanic isolation can help block noise conducted over the +5V Vbus and ground wires of a USB cable, but differential noise carried on the USB D+/D- signals is hard to block.  One good technique used by many USB re-clockers is to deploy a USB hub chip to receive the noisy USB signal from the upstream PC or streamer, and use one of the downstream-facing USB ports of the hub chip to drive the DAC with a cleaner copy of the USB signal.

 

As one of many interfaces for transporting digital audio, USB has merits of ease-of-use, easy to implement galvanic isolation, easy to implement re-clocking (e.g. with a clean powered hub chip).  From the technical point of view, I'm not surprised by the variety of USB tweak devices that have sprung up in the past few years.  These devices are relatively straightforward to design and implement, at least as compared to devices of equivalent functionality for interfaces such as S/PDIF, AES, I2S.

 

Based on recent understandings of what issues the USB interface of a DAC can suffer, I believe there will be newer DAC designs with integrated galvanic isolation, re-clocking, etc. that will render most of the existing USB tweak devices redundant.  It should only be a matter of time.  A few excellent DACs today (Phasure? Berkeley?) are already so good they don't benefit from the USB tweak boxes.  BTW, my Auralic Aries Femto / Vega DAC combo has repeatedly failed to benefit sound wise from any USB re-clocker (including W4S, UpTone Amber REGEN & ISO REGEN) or isolator (Intona) inserted between them.  I'd say overall, many current brands of DACs have a bit of catching up to do...

 

[mmerrill99]

18 minutes ago, pkane2001 said:

 

So, are you saying that USB cables improve SQ by reducing noise in the digital transmission?

 

Seems to me that a USB cable is not the best way deal with noise, and that there are much better ways to stop it from entering DAC. Galvanic isolation being one of the obvious ones. 

No that's not what I said - you need to read my post again.

[pkane2001]

3 minutes ago, scan80269 said:

I'm going to take a swag at answering your questions, though I humbly profess that I'm far from being a "know-it-all"...

 

In theory, signal integrity of USB signals entering the USB front-end of a DAC should have no effect on the digital-to-analog conversion and downstream analog output circuitry.  In reality, the quality of the USB signals arriving at the DAC USB receiver will greatly affect how hard the USB interface chip (e.g. XMOS) has to work to retrieve the bitstream.  The more active a block of digital (or digital/analog hybrid) logic works, the more power hungry it becomes so it dumps more electrical noise onto the power & ground planes it sits on.  Unless very well isolated, this electrical noise can make its way to the D-to-A conversion circuitry and induce increased jitter into the conversion, which can then be heard as degraded sound at the analog outputs.  John Swenson has explained this phenomenon in great detail.

 

A good USB re-clocker should greatly reduce the audible impact of the USB cable, though as John may have also indicated, the key word is reduce, not eliminate.  With increasing evidence that the USB data signals (D+ & D-) can carry noise in addition to the intended USB signal, coupled with USB receiver PHY's ability to attenuate common-mode noise but not differential mode noise, we probably have a scenario of some amount of noise (mostly differential) getting through to the clock and data recovery logic sections, thus inducing more activity and noise.

 

Galvanic isolation can help block noise conducted over the +5V Vbus and ground wires of a USB cable, but differential noise carried on the USB D+/D- signals is hard to block.  One good technique used by many USB re-clockers is to deploy a USB hub chip to receive the noisy USB signal from the upstream PC or streamer, and use one of the downstream-facing USB ports of the hub chip to drive the DAC with a cleaner copy of the USB signal.

 

As one of many interfaces for transporting digital audio, USB has merits of ease-of-use, easy to implement galvanic isolation, easy to implement re-clocking (e.g. with a clean powered hub chip).  From the technical point of view, I'm not surprised by the variety of USB tweak devices that have sprung up in the past few years.  These devices are relatively straightforward to design and implement, at least as compared to devices of equivalent functionality for interfaces such as S/PDIF, AES, I2S.

 

Based on recent understandings of what issues the USB interface of a DAC can suffer, I believe there will be newer DAC designs with integrated galvanic isolation, re-clocking, etc. that will render most of the existing USB tweak devices redundant.  It should only be a matter of time.  A few excellent DACs today (Phasure? Berkeley?) are already so good they don't benefit from the USB tweak boxes.  BTW, my Auralic Aries Femto / Vega DAC combo has repeatedly failed to benefit sound wise from any USB re-clocker (including W4S, UpTone Amber REGEN & ISO REGEN) or isolator (Intona) inserted between them.  I'd say overall, many current brands of DACs have a bit of catching up to do...

 

Thank you, Scan! I think you and I have very similar understanding of how these things might work. With proper isolation and circuit design to separate USB receiver from I2S output, all USB cables/regenerators/isolators should begin to sound the same. 

[pkane2001]

5 minutes ago, mmerrill99 said:

No that's not what I said - you need to read my post again.

 

Sorry if I misunderstood. Please explain how "cables can also be responsible for different profiles" is different than cables improving SQ through noise reduction. Or are you saying that USB cables can only destroy SQ?

39 minutes ago, mmerrill99 said:

It may also be a noise issue & cables can also be responsible for different noise profiles

 

[mmerrill99]

3 minutes ago, pkane2001 said:

Thank you, Scan! I think you and I have very similar understanding of how these things might work. With proper isolation and circuit design to separate USB receiver from I2S output, all USB cables/regenerators/isolators should begin to sound the same. 

That's not what he said, either.

Unfortunately, what you just posted is not the reality.

[mmerrill99]

2 minutes ago, pkane2001 said:

 

Sorry if I misunderstood. Please explain how "cables can also be responsible for different profiles" is different than cables improving SQ through noise reduction. Or are you saying that USB cables can only destroy SQ?

 

That was just one bit of what I said & not the totality - it cannot be summarised into what you said in your post - that's a misleading summary.

[pkane2001]

Just now, mmerrill99 said:

That's not what he said, either.

Unfortunately, what you just posted is not the reality.

 

You appear to have a reading comprehension issue. This is what Scan said:

23 minutes ago, scan80269 said:

Based on recent understandings of what issues the USB interface of a DAC can suffer, I believe there will be newer DAC designs with integrated galvanic isolation, re-clocking, etc. that will render most of the existing USB tweak devices redundant.  It should only be a matter of time.  

 

This is what I said:

6 minutes ago, pkane2001 said:

With proper isolation and circuit design to separate USB receiver from I2S output, all USB cables/regenerators/isolators should begin to sound the same. 

 

Where do you perceive this large difference?

[Jud]

46 minutes ago, scan80269 said:

A few excellent DACs today (Phasure? Berkeley?) are already so good they don't benefit from the USB tweak boxes.

 

Phasure has recently installed its own built in “tweak box,” the Phisolator, yet the sound is still at least purportedly affected by the USB cable.  Berkeley has for a long time had its own separate USB/SPDIF converter.  So we still appear to be a little way from at least these manufacturers attaining immunity from upstream influences in a fully USB chain.

[hols]

It so happens that I just received my Lush USB cable 3 days ago and I happen to have both Phasure NOS1a and also several other DACs including Holo Spring that I have also been testing the SOtM tx-USB Ultra (powered by JS-2)and the isoREGEN(powered by LPS1) with USPCB(burned in for the past 2 weeks). After reading through this hot thread I can't resist to plug in the Lush to replace the USPCB (see photo) in my Holo Spring line and my impression is as follows.

 

First my impression of use or not use the iosREGEN with USPCB before the SOtM tx-USB Ultra stays the same as my initial impression reported 2 weeks ago in another thread. Yes it gives a more full bodied sound and is more warm and analogue on first listening but on listening a bit longer the strings are too full bodied and lacks the transparency that is present when not using the isoREGEN. The layering that was present before is weakened. The focus of instruments are a little overblown. The orchestra cannot fly as vividly as before. (I used to test with Richter playing Brahms second piano concerto). And that is perhaps the price to pay for getting a very round and appealing sound. I think as a whole there is a bit too much mid range.

 

I then changed to the Lush cable(not really burned in yet) and I must say that this is the one. It just gives you the analogue feel together with details. The violins are silky and yet you can still hear them conveying to you the feelings. No excessive full bodied sound. And listen to the gentle decay of the sound at decrescendos and sound slowly dying away. The microdynamics are all there and most important with feeling. And when the solo piano comes in the percussive notes is both authoritative and musical. Very difficult to achieve. And the musical sound and transparency and details are always there and never gives you fatigue. I must say that this is definitely my preferred sound.

 

I think the sound can only be bettered by the Phasure NOS1a upgraded G3 which I agree is the best digital sound I have ever heard. Dynamic and yet comes with detail and feelings.( It is a PCM system and yet the musicality wins  the DSD in my other system). The only digital system that can be compared to my $30k LP system.

I have no commercial association with all the gears I have mentioned. Just an enduser reporting the end result in his own system. And I must admit too I don't have the knowledge base to understand or comment on the underlying technologies behind all these products.

[mmerrill99]

1 hour ago, pkane2001 said:

 

You appear to have a reading comprehension issue. This is what Scan said:

 

This is what I said:

 

Where do you perceive this large difference?

The difference is in where the isolation is implemented - now go back & read what you quoted of his post & spot this difference with what you posted.

[Speed Racer]

Lately,  just about any thread with manisandher posting often is an infomercial for Phasure. Usually with posts sprinkled in to bash Yggdrasil.  I can't take any of this very seriously as USB cables don't subtract noise. All they can do is alter it. Of course, the only way to get rid of the noise is with a products like the ISO Regen that isolate all the noise for the source. Now that Phasure has their own design, of course we get to hear how the ISO Regen is inferior.

 

Threads like this are useless because they are completely subjective with people that have demonstrated no ability to be unbiased.

[rikhav]

Hi hols

Very good comparison

Just to confirm, you tried the lush cable without the ISO regen , right ?

[hols]

1 minute ago, rikhav said:

Hi hols

Very good comparison

Just to confirm, you tried the lush cable without the ISO regen , right ?

With the isoREGEN replacing the USPCB as shown in the photo.

[mmerrill99]

5 minutes ago, Speed Racer said:

I can't take any of this very seriously as USB cables don't subtract noise. All they can do is alter it.

If altering this noise tenders it inaudible, is it not equivalent to removing it from audibility?

 

Anyway, cables can reduce noise as I showed with the noise plots of the Lnc cable

[Speed Racer]

21 minutes ago, mmerrill99 said:

If altering this noise tenders it inaudible, is it not equivalent to removing it from audibility?

 

Anyway, cables can reduce noise as I showed with the noise plots of the Lnc cable

 

The LNC plots showed that the reduce noise caused by EMI.  What if there is not noise caused by EMI?? What if all you have is noise put on the cable by the computer itself? 

[mmerrill99]

14 minutes ago, Speed Racer said:

 

The LNC plots showed that the reduce noise caused by EMI.  What if there is not noise caused by EMI?? What if all you have is noise put on the cable by the computer itself? 

Why would emi noise not arise from the computer itself? But you said USB cables don't reduce noise, you didn't say don't reduce noise which isn't emi - what noise are you talking about then?

 

More correctly those lnc plots show noise at high frequencies are reduced - emi, RFI - it isn't specified

[rikhav]

59 minutes ago, hols said:

With the isoREGEN replacing the USPCB as shown in the photo.

 

Sorry for the confusions, so that will involve 2 usb cables right ?

If yes both are lush cables ?

 

Have you tried the lush cable directly from pc to dac ?

 

How is the sound that way?

[Speed Racer]

23 minutes ago, mmerrill99 said:

Why would emi noise not arise from the computer itself? But you said USB cables don't reduce noise, you didn't say don't reduce noise which isn't emi - what noise are you talking about then?

 

More correctly those lnc plots show noise at high frequencies are reduced - emi, RFI - it isn't specified

 

The shielding reducing the EMI noise. So it would be external sources of EMI that would otherwise pollute the signal on the cable.

[mmerrill99]

13 minutes ago, Speed Racer said:

 

The shielding reducing the EMI noise. So it would be external sources of EMI that would otherwise pollute the signal on the cable.

It's the ferrous impregnated dielectric that affords the reduction in high frequency noise, not what is typically called the shield in a USB cable.

 

It reduces both the intrusion & the emission of RFI.

 

Could this change the noise profile reaching the receiving end of the USB cable?

 

Does it matter how the noise arises on the cable?

[fas42]

1 minute ago, mmerrill99 said:

It's the ferrous impregnated dielectric that affords the reduction in high frequency noise, not what is typically called the shield in a USB cable.

 

It reduces both the intrusion & the emission of RFI.

 

Could this change the noise profile reaching the receiving end of the USB cable?

 

Does it matter how the noise arises on the cable?

 

Okay, this looks like another case of using a semiconducting layer - the ferrous impregnated dielectric - perhaps to perform some 'magic'.

 

Perfect insulators are not always the best answer - a little bit of conductivity goes a looong way ...

[Speed Racer]

9 minutes ago, mmerrill99 said:

It's the ferrous impregnated dielectric that affords the reduction in high frequency noise, not what is typically called the shield in a USB cable.

 

It reduces both the intrusion & the emission of RFI.

 

Could this change the noise profile reaching the receiving end of the USB cable?

 

Does it matter how the noise arises on the cable?

 

Intrusion from where? Outside the cable. Emission from where? The cable. That does not mean the cable reduces any noise the computer injects into the cable via the pins in the connector. It just means the cable reduces the noise RFI would otherwise add and does not emit as much RFI as (some) other cables.