USB audio cracked... finally!

[pkane2001]

23 minutes ago, mmerrill99 said:

It may be that the USB signals withing the USB microframes (talking high speed USB 2 here) are essentially square wave electrical waveforms being communicated via the USB signal wires. These squarewaves have a risetime & falltime - anything which changes the shape of these signals from their optimal shape may well have an effect within a USB DAC - the exact mechanism of operation is still unknown 

So the problem is noise. Be careful filtering noise out using a HF filter on USB transmission -- that will also destroy the shape of the square wave by smoothing out the corners, resulting in exactly the effect you are trying to eliminate.

[mmerrill99]

19 minutes ago, pkane2001 said:

So the problem is noise. Be careful filtering noise out using a HF filter on USB transmission -- that will also destroy the shape of the square wave by smoothing out the corners, resulting in exactly the effect you are trying to eliminate.

Yes, bandwidth limiting that affects the signal shape seems to have an audible effect - this includes USB cables which are not of sufficient bandwidth.

 

If we consider USB high speed is 480Mbps or 480MHz fundamental frequency & to represent a half decent square wave requires at least 3 harmonics (some say 5 harmonics) we have a requirement for passing 480MHz X 3 = 1.44GHz bandwidth requirement for a cable or if you want to consider 5 harmonics necessary for a good squarewave then 480X5 or 2.4GHz bandwidth cable is necessary!

[mmerrill99]

23 minutes ago, scan80269 said:

I suspect there is a fair amount of unavoidable periodicity in this isochronous transfer mode.  For example, packet rate is 8KHz.  In contrast, the bulk transfer mode, by not guaranteeing transfer bandwidth or latency, may actually be less periodic in the way the data fly over the cable from sender to receiver.  Is it possibly what Peter has figured out, by making his DAC support only USB bulk transfer mode, along with a deep FIFO data buffer to smooth out the extreme irregularities of USB data arriving at the DAC?

This would require a new software driver being written so I doubt that is the approach.

The original Hiface used bulk mode USB transfer, btw

[scan80269]

27 minutes ago, mmerrill99 said:

Yes, bandwidth limiting that affects the signal shape seems to have an audible effect - this includes USB cables which are not of sufficient bandwidth.

 

If we consider USB high speed is 480Mbps or 480MHz fundamental frequency & to represent a half decent square wave requires at least 3 harmonics (some say 5 harmonics) we have a requirement for passing 480MHz X 3 = 1.44GHz bandwidth requirement for a cable or if you want to consider 5 harmonics necessary for a good squarewave then 480X5 or 2.4GHz badwidth cable is necessary!

I found this statement in the USB 2.0 Specification, for high-speed (480Mbps) transfer rate:

 

For a hub, or for a device with detachable cable, the 10% to 90% high-speed differential rise and fall times must be 500ps or longer when measured at the A or B receptacles (respectively).

 

The differential signals on the D+ & D- lines don't need to be as square as possible.  The rise/fall times need to be fast enough to pass well defined eye pattern requirements.  In modern motherboard designs with USB ports, there are often design trade-offs between USB signal integrity and EMC compliance.  Insertion of inline common mode chokes are used to mitigate EMC issues but can lead to waveform distortions that can affect transmission integrity.  These issues are observable via eye pattern measurements.

 

Alterations of USB signal rise/fall times (e.g. by a cable) can lead to timing differences at the receiver, since USB employs embedded clock technology (i.e. no separate clock wires alongside the data wires).  The USB PHY on the receiving end has to work harder to retrieve the bit stream in real time if the incoming USB signal integrity is poor.  This is now quite well understood, albeit rather recently.  There's an optimum range of rise/fall times, and anything too slow or too fast will be detrimental (in different ways).

 

So I don't doubt different USB cables can result in different sound.  Immunizing a DAC against the effects of a USB cable connected to it has not been trivial and there hasn't been a lot of success cases AFAIK.

 

[Panelhead]

15 hours ago, Speed Racer said:

 

Agreed. USB cracked is to not use it at all......

  This is a little too direct. It is good to see the progress in transmission continues to evolve. 

  Maybe the easiest approach is moving on to USB-C.

[elcorso]

Order placed !

 

Maybe the first "Lush Life in the Rainforest".  I could write a book about this 

 

Thanks Mani !

 

Roch

[pkane2001]

1 hour ago, scan80269 said:

Alterations of USB signal rise/fall times (e.g. by a cable) can lead to timing differences at the receiver, since USB employs embedded clock technology (i.e. no separate clock wires alongside the data wires).

Scan, can you please elaborate on the 'embedded clock technology'? I know how a clock is derived from an S/PDIF data stream, but how is WCLK embedded in (and derived from) the isochronous USB data packets?

[rando]

10 hours ago, manisandher said:

 

 

The Lush gives my system a 'natural' and 'analogue' sound. Instruments and voices are both full-bodied and crystal clear at the same time. The whole sound resonates beautifully, with a natural decay. How do you convey this to anyone who has only heard a typical 'digital' sound? The photos were my attempt, but obviously not as helpful as I had hoped.

 

Mani.

 

 

I gathered it was an imperfect comparison.  One that works if you don't look at the picture too closely without admitting digital still has many flaws in how it tries to be too perfect.  Thank you for addressing my question at face value, btw.    

 

It pleases me to see someone else headed in the same direction with the computer part of their system that you and acg are.  Sometimes I wonder at the lack of computer in computer audiophile.  Or more directly, acceptance of gaming parts and discrete VC's with very low build quality/high failure rate.  These two worlds are on a collision course.  Once gamers ditched sound cards for external DAC/amp boxes the jump into clean power from a quiet machine with passive heat distribution was inevitable.  A lot of them play with $13K Intel's at work all day and retired deca core chips all night.  USB 2.0 is a dead end in all but legacy applications.    

 

I'll kindly leave now and take the ability to vote with my €200 along.  Don't think I fail to appreciate every small step forward will inevitably produce large ones.  Or dispute this cable is an improvement in your system.  I just won't be buying it.

[Jud]

2 hours ago, scan80269 said:

So I don't doubt different USB cables can result in different sound.  Immunizing a DAC against the effects of a USB cable connected to it has not been trivial and there hasn't been a lot of success cases AFAIK.

 

 

In purely subjective listening, @PeterSt‘s Phasure DAC was the best I’ve ever heard at this.  I think he may have gone in a bit of an other direction since, but it shows he knows how to do it if he wants.

[manisandher]

13 minutes ago, rando said:

USB 2.0 is a dead end in all but legacy applications.    

 

It's funny, only 3 weeks ago I wrote the following on the Phasure forum: "I'm growing a real hatred for all things USB. It's like we're all being held hostage by its whims. And unfortunately, it has us by the balls..."

 

I was referring here to my DAC having only a USB 2.0 input. Being the best DAC I've ever heard, I have no choice but to use USB.

 

13 minutes ago, rando said:

I just won't be buying it.

 

Never say never. You may change your mind once others' opinions of the Lush start coming in.

 

Mani.

[Dev]

Just when I thought the end of the USB cable with USPCB, a new cable arrives! Interesting. I haven't heard the USPCB myself (since I can't seem to buy one from their website) but I am very keen in hearing how this cable sounds in other setups apart from Phasure (which OP has been a strong supporter of). I don't really care if it follows USB spec or not but if the Lush (200 euro ?) can replace my Audience AU24, nothing like it. I am following this thread closely.

 

Btw, both the pictures posted of the glamour women are mediocre at best - the left one is over-shappened and the other removes all the details and seem to apply too much gaussian blur (smooth) effect. I hope Lush doesn't sound "like" the later one as the OP seems to indicate.

[Ralf11]

"mass of the connectors"  ????

[jabbr]

1 hour ago, manisandher said:

It's funny, only 3 weeks ago I wrote the following on the Phasure forum: "I'm growing a real hatred for all things USB. It's like we're all being held hostage by its whims. And unfortunately, it has us by the balls..."

 

It is perplexing that despite purported improvements in USB isolation there are still ?dramatic? differences in the "sound" of USB cables? I'd think that the goal of USB isolation/reclocking/regeneration is to eliminate the vagarities of cable impedance etc. @PeterSt : I would really like a technical explanation if feasible.

[manisandher]

12 minutes ago, Dev said:

I hope Lush doesn't sound "like" the later one as the OP seems to indicate.

 

Uh, no:

 

On 7/14/2017 at 4:15 PM, manisandher said:

It’s difficult explaining the sound of the Lush, though the name should give a clue. Another Lush owner came up with the following image:

 

To my ears, the Lush makes my system sound totally natural and 'analogue'. Instruments and voices have a rich harmonic texture, and yet sound crystal clear. I can see that the right image doesn't quite do this justice.

 

Mani.

[Dev]

4 minutes ago, manisandher said:

 

Uh, no:

 

 

To my ears, the Lush makes my system sound totally natural and 'analogue'. Instruments and voices have a rich harmonic texture, and yet sound crystal clear. I can see that the right image doesn't quite do this justice.

 

Mani.

 

Fair enough. Has anybody yet tried on a non-Phasure system (both DAC and PC & s/w) and thinks it's an end-game as well ? I believe the other poster of Lush is also a Phasure user.

[Dev]

17 minutes ago, jabbr said:

 

It is perplexing that despite purported improvements in USB isolation there are still ?dramatic? differences in the "sound" of USB cables? I'd think that the goal of USB isolation/reclocking/regeneration is to eliminate the vagarities of cable impedance etc. @PeterSt : I would really like a technical explanation if feasible.

 

Good question but even with external isolators & reclockers, like Intona and ISO-Regen, the USB cable matters. Folks have gone as far as saying that the uspcb before and after makes dramatic differences. If it matters for external boxes, why won't it matter when these functions are implemented inside the DAC ?

[mmerrill99]

2 hours ago, pkane2001 said:

Scan, can you please elaborate on the 'embedded clock technology'? I know how a clock is derived from an S/PDIF data stream, but how is WCLK embedded in (and derived from) the isochronous USB data packets?

If I can answer for Scan - I believe what he means is not that the audio clock is embedded in the USB data packets but rather that the USB specification states USB frames are sent every 1mS & high speed microframes are meant to be sent every 125uS i.e 8 microframes per 1mS frame or the 8KHz periodic current burst sometimes reported. There is a certain +/- tolerance on these timings in the USB spec. The PC's USB clock usually times this but in asynchronous USB the USB receiver's local USB keeps it's local buffers half full by sending back signals to the PC about how much data should be in the next microframe.   

[jabbr]

57 minutes ago, Dev said:

 

Good question but even with external isolators & reclockers, like Intona and ISO-Regen, the USB cable matters. Folks have gone as far as saying that the uspcb before and after makes dramatic differences. If it matters for external boxes, why won't it matter when these functions are implemented inside the DAC ?

Again, I'd like to hear the details but I am concerned that this implies that the USB protocol stack is not optimal for audio as designed. We now are talking about a protocol that looks like USB but with a different PHY layer. 

 

My understanding of USPCB is that great care is taken to conform to the USB specification.

[mmerrill99]

1 hour ago, jabbr said:

 

It is perplexing that despite purported improvements in USB isolation there are still ?dramatic? differences in the "sound" of USB cables? I'd think that the goal of USB isolation/reclocking/regeneration is to eliminate the vagarities of cable impedance etc. @PeterSt : I would really like a technical explanation if feasible.

Yea, it's perplexing that there can be audible differences - I wouldn't call them dramatic, though.

 

One of the problems is that with a USB cable change there are a number of variables being changed at once

- impedance & it's variability along the length of the cable

- cable bandwidth

- ground noise

- shield strength

 

If only one of these variables was changing between cables, we might be able to get a handle on what's going on?

[mmerrill99]

19 minutes ago, jabbr said:

My understanding of USPCB is that great care is taken to conform to the USB specification.

Yes but is it due to other factors that cables suffer from - I don't know, I'm just asking ?

- variable impedance along the cable length

- shielding (how is the USPCB shielded)

- grounding - what is the grounding config?

- 5V supply - how is this configured on the pcb?

[Dev]

20 minutes ago, jabbr said:

Again, I'd like to hear the details but I am concerned that this implies that the USB protocol stack is not optimal for audio as designed. We now are talking about a protocol that looks like USB but with a different PHY layer. 

 

 

Yes, off coarse - usb was never designed for audio in the first place and as a result there are proliferation of usb "conditioners" in the market today. Its interesting to see the results of this cable on a non-phasure based system. I am not too sure if the change in the cable design/material would change the PHY drastically. Nevertheless, I would like to hear details as well.

 

 

20 minutes ago, jabbr said:

My understanding of USPCB is that great care is taken to conform to the USB specification.

 

So now we have two contradicting theories - one that is designed precisely to follow usb spec and the other which moves deliberately away from it. A comparison between the two is in high order

 

[acg]

6 hours ago, ClothEars said:

 

I will be very interested to hear your thoughts on the Lush and the Curious cables. In fact if you are in Brisbum I use Curious cables and would be happy to host a test.

 

That should be possible.  I am in Toowoomba though but do get down to BrisVegas from time to time.  Either PM me here or on SNA and we should set up a get together.

 

EDIT:  I should mention that my The Lush is 1.5m long and hope that it will fit into your rack.

[acg]

All this talk about technical directions that the cable may have gone in but there is also a physical direction as well.  Peter has mentioned at his website that the cable is designed to bend in specific directions at or near the connectors and that this is something specific to the functioning of the cable. 

 

Also he has paid specific attention to dielectric and other effects more commonly associated with analogue cables.

[Jud]

5 minutes ago, acg said:

 

Also he has paid specific attention to dielectric and other effects more commonly associated with analogue cables.

 

Of course it shouldn’t be forgotten that in some respects “digital” cables do transmit analog signals.

[scan80269]

1 hour ago, mmerrill99 said:

If I can answer for Scan - I believe what he means is not that the audio clock is embedded in the USB data packets but rather that the USB specification states USB frames are sent every 1mS & high speed microframes are meant to be sent every 125uS i.e 8 microframes per 1mS frame or the 8KHz periodic current burst sometimes reported. There is a certain +/- tolerance on these timings in the USB spec. The PC's USB clock usually times this but in asynchronous USB the USB receiver's local USB keeps it's local buffers half full by sending back signals to the PC about how much data should be in the next microframe.   

Thanks, mmerrill99!

 

Yes, 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.  For example, the 22.5792MHz audio clock reference is used to re-clock an audio stream carrying 44.1K/88.2K/176.4K/352.8K sampling rate (including Redbook 16/44.1K CD audio).  This re-clocking is often done with a block of digital logic implemented with an FPGA such as from Xilinx or Altera.  A data stream buffer (FIFO) is used to tolerate disruptions or underfeeding of audio data coming from USB.  Over-sampling of the audio ahead of the digital-to-analog conversion can involve the use of custom DSP hardware as well.

 

The USB receiver HW in a DAC, e.g. XMOS chip can be a significant source of electrical noise, so galvanic isolation of the USB receiver section from the rest of the DAC has become increasingly popular in newer DAC or DDC designs.  Technically it can be more challenging to design a DAC to sound as good with its USB input than with other digital audio inputs (that carry embedded or explicit audio clocks), but there's no compelling reason to summarily dismiss USB as an inferior digital audio transport.  Good (or bad) implementation can easily make a larger difference than the type of transport interface.