USB Cables....

I think we all know by now what this section is for.
David
User
Posts: 123
Joined: Wed Jan 05, 2011 3:12 pm

#16

Post by David »

Hi Neal, All,
Sure, I'm not saying the improvement is necessarily due to the silver, although I can easily make of two of the Clive leads one with silver, one with copper to see if I can detect any difference.

The lead I replaced was one supplied by Wavelength with a DAC, and you would expect them to have done some research and included a lead which did their DAC justice. Indeed, the instructions even state that the USB lead is not critical and advise against spending much money here, telling you how the included one is very adequate.

As Clive says the JK DAC does not use the V+ and it has no sleep function. Using my new lead on the laptop last night the data did drop out a few times, so it seems I just have a good old bad connection on one of the plugs. That same bad connection obviously affects the Arcam less (not at all in fact).

Going back to silver, I have had god results using silver leads for data transmission. But of course, the geometry was radically different, so it will be interesting to do a like for like with the Clive cable!
David
David
User
Posts: 123
Joined: Wed Jan 05, 2011 3:12 pm

#17

Post by David »

And PS, Clive, were you suggesting there is an improvement in removing the v+ even when this isn't used a la JK Dac?
Clive
Old Hand
Posts: 374
Joined: Tue May 22, 2007 9:17 am
Location: Cheshire, England

#18

Post by Clive »

David wrote:And PS, Clive, were you suggesting there is an improvement in removing the v+ even when this isn't used a la JK Dac?
Yes, getting polluted power, even with no current draw, worked in my case but every USB port has a different noise profile so I expect it's impossible to generalise.
gazjam
User
Posts: 103
Joined: Sat May 05, 2012 1:21 pm

#19

Post by gazjam »

subjectively,
I'd always put any difference with digital kit down to it NOT just being 1's and 0's....

I believe there's an analogue component to USB that perhaps we don't fully understand yet.
I was at Ali's when we heard USB cables making a difference, question is why?
In my own dabbling I've isolated the 5v power line from both cheap and not so cheap USB cables and they still sound different...so its not clean power/galvanic issues.
JamesD
Old Hand
Posts: 997
Joined: Tue Oct 09, 2007 4:26 pm
Location: North Yorkshire

#20

Post by JamesD »

Well there is certainly an analogue part to any digital signals transmission from one point to another and its pretty well understood and definitely measurable.

The "eye's" have in in this case... In digital signal transmission the one's and zeros can be overlapped around their ideal position (in time) on a scope and a thing called the eye display results. It shows the bit edges both up edges and down edges and any noise, jitter, attenuation and distortion of the digital signal - it also graphically shows the difficulty the receiver is going to have in locking onto the signal and how hard the following circuitry will have to work to reconstitute the digital signal - it is this that causes the following DAC or other digital processing circuits to change the sound of the resulting audio signal that our ears are exposed too..

Nothing magic - in the digital domain its all good solid analogue engineering :lol:

J
User avatar
Nick
Site Admin
Posts: 15709
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#21

Post by Nick »

However unlike spdiff, the incoming USB frames and the output data (application layer) is far more decoupled from the cable (network layer). The USB endpoint is sent data in blocks, and so its not in real time, its bursty, so the data rate out is governed by a local clock (asynchronous) or a recovered clock (isochronous).
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
JamesD
Old Hand
Posts: 997
Joined: Tue Oct 09, 2007 4:26 pm
Location: North Yorkshire

#22

Post by JamesD »

data rate out is indeed re-clocked - and that means that any read-in errors of the bitstream into the data frame have a tendency to become imprinted in the signal as if part of the original digitisation... although it can deal nicely with transmission errors.

I like USB connections for audio - up to a point - but generally the usb bus is a noisy place so steps have to be taken both to get the signal into the USB frames without damage and to get the frame transmitted cleanly...

Multiple levels of abstraction of digital signal from analogue environment can help preserve the original signal but they can also hinder getting back to the original if it has been damaged before the abstraction is applied...

J.
User avatar
Nick
Site Admin
Posts: 15709
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#23

Post by Nick »

Yep, but there is a frame CRC, so minor errors will lead to gross dropout. Just saying.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Neal
Shed dweller
Posts: 2299
Joined: Fri Aug 03, 2007 10:57 am
Location: From the land of the Bodgers

#24

Post by Neal »

I think we maybe barking up the wrong tree looking for causes in the data stream itself. I have a feeling any effects are more secondary in nature and related to improper termination, non ideal impedance of the cable or circuit layout with possible effects around common mode noise rejection of the differential signaling pair....oh and non isolation of the signal pair and ground plane in the DAC.

Given the isolation you have built into your DAC Nick have you noticed any differences in sound with different cables?
User avatar
Nick
Site Admin
Posts: 15709
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#25

Post by Nick »

No, but to be honest Neal I have not had a chance to do the comparison.

But yes, I would tend to suspect you are right, the USB cable offers a nice aerial extending the 0v from the dac out into the wide (and noisy) world.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
gazjam
User
Posts: 103
Joined: Sat May 05, 2012 1:21 pm

#26

Post by gazjam »

I think theres something going on with the "signal" feed as well, probably in the analogue domain?

I've always attributed any differences in USB to the clean/dirty 5V power feed..but even isolating the 5V feed, cables sound different through the same Dac.

Odd!
User avatar
Nick
Site Admin
Posts: 15709
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#27

Post by Nick »

Yep, but most implementations take the 0v line into the DAC circuit, so link the source supply and DAC supply via their grounds. Doesn't matter if 5v is decoupled.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Neal
Shed dweller
Posts: 2299
Joined: Fri Aug 03, 2007 10:57 am
Location: From the land of the Bodgers

#28

Post by Neal »

Yes, as PC/Laptop supplies tend to be floating with no ground as such the noise is common to both the 5v rail and the 0v one.
User avatar
Paul Barker
Social Sevices have been notified
Posts: 8874
Joined: Mon May 21, 2007 9:42 pm

#29

Post by Paul Barker »

Probably not related but my laptop ground is lifted in it's smps, yet, peculiarly, the amp sounds better when the laptop is charging than when it is on battery, go figure? but this is through the minijack.
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
Post Reply