USB audio cracked... finally!

[semente]

Is this the time when you finally discuss cartridge loading and SI? 

[pkane2001]

22 minutes ago, manisandher said:

Well let me tell you that compared to the Lush, this cable (and the other USB2 certified cables I have) sounds totally boring. The sound is smeared and veiled. There is zero musicality. It really wouldn't matter how good the rest of your system was, if you were using one of these, the musicality would be utterly non-existent.

 

Either there's something wrong with your system, or my system is just significantly better   I've been using stock and modified $4 USB cables, and my system sounds not just musical, but the best it's sounded in over 20 years.  Zero musicality and totally boring is definitely not the way I would describe the sound I hear. Involving, enveloping, natural-sounding, wide and deep soundstage, engaging, musical. While I can imagine that Lush might make a difference (based on some of the proposed theories and mechanisms that have been discussed in this thread), I seriously cannot imagine anything but a small, incremental improvement to what I'm hearing now. Maybe I just lack imagination

[marce]

The USB two minimum rise time is 4ns.

Rise time is the official term for transition time, it is the rise time that determines whether a signal has to be treated as high speed. Generally the 10%-90% of the actual signal transition from 0V to Vcc is used, though just to confuse things IBIS (Input output buffer information specification) uses 20%-80% of the full transition.

Bandwith for digital signals is determined by Fknee=0.35/Rt 10-90%

 

Jabbr, if you terminate with just a resistor only you reduce the level the wave will ultimately reach due to the potential divider effect of the resistor... usually to reduce ringing you use a resistor down to ground. I prefer ac termination, where you use a resistor in series with a cap to ground,  this keeps the levels intact, but will reduce the ringing still. The best source of info for this is chapter 6 of this:

https://www.amazon.co.uk/d/cka/High-Speed-Digital-Design-Prentice-Modern-Semiconductor/0133957241

 

[lmitche]

7 minutes ago, marce said:

The USB two minimum rise time is 4ns.

Rise time is the official term for transition time, it is the rise time that determines whether a signal has to be treated as high speed. Generally the 10%-90% of the actual signal transition from 0V to Vcc is used, though just to confuse things IBIS (Input output buffer information specification) uses 20%-80% of the full transition.

Bandwith for digital signals is determined by Fknee=0.35/Rt 10-90%

 

Jabbr, if you terminate with just a resistor only you reduce the level the wave will ultimately reach due to the potential divider effect of the resistor... usually to reduce ringing you use a resistor down to ground. I prefer ac termination, where you use a resistor in series with a cap to ground,  this keeps the levels intact, but will reduce the ringing still. The best source of info for this is chapter 6 of this:

https://www.amazon.co.uk/d/cka/High-Speed-Digital-Design-Prentice-Modern-Semiconductor/0133957241

 

Here is a free TI paper covering various termination approaches.  Marce, have you seen this before? Seem useful?

http://www.ti.com/lit/an/snla034b/snla034b.pdf

[manisandher]

13 minutes ago, pkane2001 said:

Either there's something wrong with your system, or my system is just significantly better   

 

Neither 

 

13 minutes ago, pkane2001 said:

Involving, enveloping, natural-sounding, wide and deep soundstage, engaging, musical.

 

Yep, that's exactly how I would have described my sound too, with the USB cable I'd been using for the last couple of years. I was quite happy with my 10 year-old Pioneer plasma TV... until I saw an OLED a few months back...

 

13 minutes ago, pkane2001 said:

While I can imagine that Lush might make a difference (based on some of the proposed theories and mechanisms that have been discussed in this thread), I seriously cannot imagine anything but a small, incremental improvement to what I'm hearing now. Maybe I just lack imagination

 

Maybe.

 

We'll have opinions of other non-Phasure users soon. I hope they'll be such that you'll take the plunge too. Happy to then resume our little chat...

 

Mani.

[Jud]

17 minutes ago, pkane2001 said:

 

Either there's something wrong with your system, or my system is just significantly better   I've been using stock and modified $4 USB cables, and my system sounds not just musical, but the best it's sounded in over 20 years.  Zero musicality and totally boring is definitely not the way I would describe the sound I hear. Involving, enveloping, natural-sounding, wide and deep soundstage, engaging, musical. While I can imagine that Lush might make a difference (based on some of the proposed theories and mechanisms that have been discussed in this thread), I seriously cannot imagine anything but a small, incremental improvement to what I'm hearing now. Maybe I just lack imagination

 

I’ve never heard the Clairixa or Lush.  Best subjectively for me so far is the UpTone USPCB (small adapter, not cable), which if I understand correctly is not yet available separately, but is planned to be, at a price under $40.

[jabbr]

15 minutes ago, marce said:

Jabbr, if you terminate with just a resistor only you reduce the level the wave will ultimately reach due to the potential divider effect of the resistor... usually to reduce ringing you use a resistor down to ground. I prefer ac termination, where you use a resistor in series with a cap to ground,  this keeps the levels intact, but will reduce the ringing still. The best source of info for this is chapter 6 of this:

https://www.amazon.co.uk/d/cka/High-Speed-Digital-Design-Prentice-Modern-Semiconductor/0133957241

 

I have both books, yes. Up closer to the beginning of the thread I had suggested that using some capacitance in the USB termination would have the effect of increasing the rise time (I've used Transition time because people often replace increasing rise time with increasing rise speed and it's the opposite  

 

@PeterSt -- I think that if a designer has a choice of the interface , one could fold many transmission line effects of a cable into the receiver itself eg you might have altered the Phisolator's termination rather than introduce a cable -- obviously for the majority of situations one doesn't have the choice of altering the receiver so I can see justification for building specific transmission line characteristics into the cable.

[jabbr]

1 hour ago, marce said:

Jabbr, if you terminate with just a resistor only you reduce the level the wave will ultimately reach due to the potential divider effect of the resistor.

I was looking at Johnson's "High Speed Signal Propagation" (advanced black magic) 1.5 p27 Figure 1.7 where the use of a low-pass filter to shape the digital signal edges creating a finite rise/fall time is demonstrated. 

 

I cant afford/justify the fancy software so I'm just doing thus by reading and by hand. I find board layout very enjoyable.

 

For everyone else -- we've been hearing for years why it's not physically possible for cables to have a sound and why all of this is just snake oil -- so bear with me a bit on these technical details because I'm trying to provide a rational explanation of how there is at least a mechanism for cables and interfaces to have an effect.

[marce]

1 hour ago, lmitche said:

Here is a free TI paper covering various termination approaches.  Marce, have you seen this before? Seem useful?

http://www.ti.com/lit/an/snla034b/snla034b.pdf

Yes, its probably easier to follow than Howard Johnson's stuff, less maths...

[manisandher]

23 minutes ago, jabbr said:

... so bear with me a bit on these technical details because I'm trying to provide a rational explanation of how there is at least a mechanism for cables and interfaces to have an effect.

 

Absolutely! It's fascinating stuff.

 

Mani.

[marce]

26 minutes ago, jabbr said:

I was looking at Johnson's "High Speed Signal Propagation" (advanced black magic) 1.5 p27 Figure 1.7 where the use of a low-pass filter to shape the digital signal edges creating a finite rise/fall time is demonstrated. 

 

I cant afford/justify the fancy software so I'm just doing thus by reading and by hand. I find board layout very enjoyable.

 

For everyone else -- we've been hearing for years why it's not physically possible for cables to have a sound and why all of this is just snake oil -- so bear with me a bit on these technical details because I'm trying to provide a rational explanation of how there is at least a mechanism for cables and interfaces to have an effect.

I'll dig it out and have a look, but he is talking theoretical, impossible to get an infinate rise time with components.

The advantage of the SIV software is it does ALL the maths and 3D field solving for you and presents the data as pretty pictures so that even dummies like me can get to grips with it. I found being able to see pictures of what is happening makes reading the books a lot easier, its what is bringing SIV down to the masses, if you can call £10K cheep for the average SIV add on to the basic software package.

Look for Eric Bogatin's "No myths allowed" series, again a good read, with watered down maths....

[lmitche]

1 hour ago, jabbr said:

 

I have both books, yes. Up closer to the beginning of the thread I had suggested that using some capacitance in the USB termination would have the effect of increasing the rise time (I've used Transition time because people often replace increasing rise time with increasing rise speed and it's the opposite  

 

@PeterSt -- I think that if a designer has a choice of the interface , one could fold many transmission line effects of a cable into the receiver itself eg you might have altered the Phisolator's termination rather than introduce a cable -- obviously for the majority of situations one doesn't have the choice of altering the receiver so I can see justification for building specific transmission line characteristics into the cable.

Jabbr, I recently stuck an previously unused IFI iDefender into the DAC at end of my USB chain and have heard SQ benefits very similar to what Mani describes here. So this may be an example of the termination approach by altering the receiver,  FYI this device is intended to be used at the PC end, not the DAC end of the chain.  So much for intentions.

 

Hopefully I'll have a Lush cable here by the end of the week. It will be interesting to hear the difference, separately and combined with the iDefender.

[pkane2001]

2 hours ago, jabbr said:

I was looking at Johnson's "High Speed Signal Propagation" (advanced black magic) 1.5 p27 Figure 1.7 where the use of a low-pass filter to shape the digital signal edges creating a finite rise/fall time is demonstrated. 

 

I cant afford/justify the fancy software so I'm just doing thus by reading and by hand. I find board layout very enjoyable.

 

For everyone else -- we've been hearing for years why it's not physically possible for cables to have a sound and why all of this is just snake oil -- so bear with me a bit on these technical details because I'm trying to provide a rational explanation of how there is at least a mechanism for cables and interfaces to have an effect.

 

So, as I was saying earlier: a low-pass filter. Is there a reason not to filter out most of the higher harmonics and get closer to a pure sinewave shape for each pulse? At least this will reduce any ringing around the edges of the 'square' wave possibly reducing jitter in the USB data stream and reducing higher frequency noise. I assume the receiver circuit will still get triggered when the amplitude of the sinewave rises/falls above some threshold, no?

 

[Jud]

12 minutes ago, pkane2001 said:

a low-pass filter. Is there a reason not to filter out most of the higher harmonics and get closer to a pure sinewave shape for each pulse?

 

Does the low pass filter have its own ringing, or is that true only of digital filters?

[PeterSt]

10 minutes ago, Jud said:

Does the low pass filter have its own ringing, or is that true only of digital filters?

 

Analog just the same.

 

Weren't you the one referring to loudspeakers ringing just the same ? I could be wrong. 

Anyway it would be because of the filters (IIR).

[pkane2001]

10 minutes ago, Jud said:

 

Does the low pass filter have its own ringing, or is that true only of digital filters?

What I called 'ringing' there was the deviation from square edges around the corners of a square wave due to a band-limited transmission. 

[PeterSt]

29 minutes ago, pkane2001 said:

So, as I was saying earlier: a low-pass filter. Is there a reason not to filter out most of the higher harmonics and get closer to a pure sinewave shape for each pulse? At least this will reduce any ringing around the edges of the 'square' wave possibly reducing jitter in the USB data stream and reducing higher frequency noise.

 

Not bad thinking. But a filter set up like what's implied (resistors etc., opamps - that is, if you refer to that (I did not really look, sorry)), then I would not do that because of the variance in resistance (or capacity) because of heatup of the "filter" itself, which would be dependent on frequency etc. etc. etc. (even a kind of oscillation could be your share).

The result is that now the slope to trigger on is not consistent and that implies jitter and ...

... and maybe that is not important but ...

 

[Jud]

6 minutes ago, PeterSt said:

 

Analog just the same.

 

Weren't you the one referring to loudspeakers ringing just the same ? I could be wrong. 

Anyway it would be because of the filters (IIR).

 

Hi Peter.  No, not ringing (speakers are going to “ring” because it’s impossible for them not to, at least with current technology).  When talking about filters in crossovers I meant the effect of phase on timing and thus localization/imaging, so group delay and dispersion rather than ringing.

[PeterSt]

OK Jud.

[jabbr]

34 minutes ago, pkane2001 said:

 

So, as I was saying earlier: a low-pass filter. Is there a reason not to filter out most of the higher harmonics and get closer to a pure sinewave shape for each pulse? At least this will reduce any ringing around the edges of the 'square' wave possibly reducing jitter in the USB data stream and reducing higher frequency noise. I assume the receiver circuit will still get triggered when the amplitude of the sinewave rises/falls above some threshold, no?

 

 

Yes but to be clear, there's a whole book of math behind the diagram I posted

 

Looking at the USB sec, the rise time is min 4ns and max 20ns which is not a perfect 0ns rise time on a perfect square wave. To be very precise one would measure the signal at the output transmitter and again at the output of the cable. Every cable will have transmission line characteristics. One could then tune the bypass caps, resistors such that the receiver sees the optimal rise time.

 

My point is that although these concepts are in both publicly available literature as well as well respected books, until probably this thread, I haven't heard these concepts being discussed in the "audiophile" community.

 

So yes, having both resistors and capacitors, as well as the invariable lead inductance, as well as the invariable cable inductance and capacitance and resistance, this is indeed a "low pass filter" but the filter is not of the audio signal, rather the digital carrier of the analog signal ... 

[Jud]

1 minute ago, jabbr said:

rather the digital carrier of the analog signal ... 

 

I’m accustomed to thinking of it the other way round.

[pkane2001]

 

1 minute ago, Jud said:

 

I’m accustomed to thinking of it the other way round.

 

It's analog signal carrying digital carrier for another analog signal

 

[Jud]

3 minutes ago, pkane2001 said:

 

 

It's analog signal carrying digital carrier for another analog signal

 

 

 

[mmerrill99]

Ok, so we have 3 possible factors at play that I can tease out ATM:

- when risetime is fast it may be more difficult to ensure consistency in the timing - it's this inconsistent timing that leads to jitter & this is audible

- when risetime is slow it may be easier to ensure consistency so less jitter (as against slower risetimes leading to more uncertainty in transition point)

- when risetime is slow there may be less ringing & this may over-ride the jitter issue?

[Jud]

13 minutes ago, PeterSt said:

OK Jud.

 

That sounds like a raised eyebrow. 

 

I think that I like minimum phase filtering less in my system, because it sounds to me like the imaging and localization aren't quite as good.  I could of course be imagining this, or if I'm not, the cause could certainly be something other than phase effects.