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USB audio cracked... finally!


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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.

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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. 

 

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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

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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. 

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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.

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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. 

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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

 

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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.

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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.

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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?

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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.

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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

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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? 

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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

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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?

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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.

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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?

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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 ... ^_^

Frank

 

http://artofaudioconjuring.blogspot.com/

 

 

Over and out.

.

 

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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.

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