[chinesekiwi]

Quote:

I'm pretty sure it's a given that different cables can have different levels of jitter.  After all, isn't the USB spec designed to reduce jitter as much as possible?  The real question is whether or not the miniscule differences in jitter from one cable to another is audible or even measurable in the audio signal.

 
Measureable? probably. Within the limits of human hearing? laughable.
Jitter and stereo crosstalk are non issues in audio these days.

 

[Prog Rock Man]

Quote:

 
You're still at it after 36 pages ? And not a single one of you living in the English speaking world was able to locate the January issue Hi-Fi news (in which Paul Miller apparently demonstrates through measurements that different usb cables cause different levels of jitter in the DAC they feed) ?
 
You really don't value your time... you could be debating what level of jitter is audible, imagine how much funnier it would be 

 
 
PS: there are buffers in modern SPDIF receivers. 

   Those are actually working in a very similar way to the buffers in the most common USB receivers (but not in the same way as the buffers inside asynchronous usb receivers... ooh the joy of multiple protocols on the same interface); that allowed TI to share the SPACT technology in between their spdif receivers (dir1703) and usb receivers (early pcm270*). The buffers inside the computer are pretty much irrelevant to a discussion about usb cables on the other hand.

That Paul Miller finds a difference is only part of the issue. Cable makers do that all of the time, it is part of their marketing, our cable is different so it is better. The latter part being suggestion. I take it Paul Miller has no evidence of audibility.

 

[00940]

  you guys are so predictable.
 
Obviously, the differences are measurable at the analog output of the DAC; that's by analyzing the audio signal at the analog output that jitter is most commonly measured today (as it doesn't require to open and hack the DAC unit under test).
 
Paul Miller's tests indeed don't establish audibility by themselves (did anyone say that, certainly not I ?). They deal with whether or not USB cables have various levels of performances and up to what point. It's however enough to prove wrong all the guys who seem happy to just repeat ad nauseum "it's all digital, cables can't possibly make any difference, blah blah".
 
However, by establishing the actual differences in between cables, those tests either allow to dismiss the audibility of those variations in technical performance or not, in relation with jitter audibility baselines established best through DBT.
 
Which brings me back to my original statement: usb cables do make differences, but those differences are likely too small to be audible. I'm just waiting to get the figures from the article to be confirmed in my opinion.

 

[Willakan]

This article isn't hosted anywhere on the internet, only seems to exist in print

 

[svyr]

This article isn't hosted anywhere on the internet, only seems to exist in print

you can get the december issue (arrrg, matey... ) but it errr kinda says (p94) interconnects/etc in the jan issue and no one has 'arrr, mateyed' that yet .
Maybe we can all chip in $2 to get the Jan issue for the lolz. (provided they accept paypal, since there is no way in hell anyone reasonable should give them their CC details since chances are they're not securely processed or stored . At the very least the subscription site is broken and displays 'Text goes here' lol and the subscription issue preview site section says 'you don't have access to the subscription material' without showing anything (eeeh,ok, what's the point of a preview then))
On a sidenote, there are at least 5 ads for cables in the issue, and at least 1 usb. (ADC) (there's an ad on every second page lol, it's like the hi-fi equivalent of a fashion magazine )

 

[drez]

hmm yeah looked at the site, $31 AU isn't much but I'm not interested in most of the crap in hifi magazines.

 

[Prog Rock Man]

Quote:

  you guys are so predictable.
 
Obviously, the differences are measurable at the analog output of the DAC; that's by analyzing the audio signal at the analog output that jitter is most commonly measured today (as it doesn't require to open and hack the DAC unit under test).
 
Paul Miller's tests indeed don't establish audibility by themselves (did anyone say that, certainly not I ?). They deal with whether or not USB cables have various levels of performances and up to what point. It's however enough to prove wrong all the guys who seem happy to just repeat ad nauseum "it's all digital, cables can't possibly make any difference, blah blah".
 
However, by establishing the actual differences in between cables, those tests either allow to dismiss the audibility of those variations in technical performance or not, in relation with jitter audibility baselines established best through DBT.
 
Which brings me back to my original statement: usb cables do make differences, but those differences are likely too small to be audible. I'm just waiting to get the figures from the article to be confirmed in my opinion.

I totally agree with your points 0094, I just wanted to confirm whether or not there was any comment on audibility.

 

[dvw]

I am having a little problem understanding the jitter in the streaming vs jitter in the playback. Can someone explain this to me.
Let's assume for ease of understanding a recording is recorded at 44KHz and this recording should be played back at 44KHz and not 44.1KHz. If not this will cause a buffer under run.
The USB2.0 is streamed at 480Mbps. How is this frequency related to the playback clock? How is the exact playback clock recovered?
If the playback clock is not recovered from the streaming/USB clock, how is jitter in the USB clock affect playback clock?
If it does, will playing at a lower speed (USB1.1) or higher speed (USB3.0) make any difference?

 

[labrat]

Delete

 

[00940]

Quote:

I am having a little problem understanding the jitter in the streaming vs jitter in the playback. Can someone explain this to me.
Let's assume for ease of understanding a recording is recorded at 44KHz and this recording should be played back at 44KHz and not 44.1KHz. If not this will cause a buffer under run.
The USB2.0 is streamed at 480Mbps. How is this frequency related to the playback clock? How is the exact playback clock recovered?
If the playback clock is not recovered from the streaming/USB clock, how is jitter in the USB clock affect playback clock?
If it does, will playing at a lower speed (USB1.1) or higher speed (USB3.0) make any difference?

 
The answer is "it depends". The problem is indeed to match two clocks : the sending or streaming clock and the playback clock. To make things easy:
 
In some USB audio protocols, the playback clock is based upon the streaming clock. The playback clock will vary over time to adapt (which means keeping a relatively constant relationship) to the incoming clock in order to avoid the small fifo buffer running empty or overflowing (it's no big deal for audio playback if we play 44.1khz material a bit slower or a bit faster, as long as it doesn't change quickly). If it is properly done, the recovery process will smooth out most of the jitter of the streaming clock. The final jitter of the playback clock (the one that could possibly matter) will depend on the quality of the clock recovery process and on the quality of the streaming clock (as we can't expect the recovery process to be perfect), as well as on the quality of the hardware implementation.
 
In another USB audio protocol (the famous asynchronous one), the playback clock is in charge and the usb receiver will signal the source computer to adapt its streaming of data if the buffer is nearing emptiness -  overflowing. The jitter of the playback clock can only be attributed to the quality of the local clock (which can vary quite a lot depending on hardware implementations), the jitter of the streaming clock becoming irrelevant.
 
 
Did you read those articles ? They might clear up some of your questions:
 
http://www.eetimes.com/design/audio-design/4009467/The-D-A-diaries-A-personal-memoir-of-engineering-heartache-and-triumph
http://www.eetimes.com/design/audio-design/4009466/Do-we-use-an-existing-USB-core-How-large-should-the-FIFO-be-The-D-A-Diaries-Part-2
http://www.eetimes.com/design/audio-design/4009528/Meeting-the-Distortion-Goals-The-D-A-Diaries-Part-3-of-3
 
This one is interesting too, a bit too complicated maybe: http://www.audiomisc.co.uk/Linux/Sound3/TimeForChange.html

 

[dvw]

Thanks. I think I understand now. I was under the impression there is only one class of USB audio device that behaves somewhat like RTP/RTCP with embedded clock in the packet instead of the bit stream. In reality, the clock performance is really dependent on the implementation of the clock recovery circuit rather than a standard based solution.
 
The playback clock depends on the implementation will have a varied degree of jitter and that should dominate over any jitter generated by the cable. And this jitter cannot (or unlikely) be reduced because it's caused by the differential of the receiver and transmitter. Well, at least that's my conclusion.

 

[High_Q]

Guys, I don't really see much point to this discussion if you do not have much grasp of the technology. I think designing a usb circuitry will give you good enough insight, and all others claiming cable issues without real understanding is really bothering me.  It just seams like a waste of time.  Anybody comp E?  Comp Es should have sufficient knowledge to explain all this.  As a EE(with limited knowledge of CE), if you cannot explain how the tech works, you do not have the credibility to make assumptions on the causes, and no, what you read on google or forums doesn't count.

  My 2 cents.

 

[leeperry]

hehe, the thread that will never die

 
I really wish that all the USB cables sounded the same, this would have saved me a lot of headaches...but luckily after trying zillion cables ranging from $1 to $150, my fav sounding cable costs $5, hallelujah! And yes, it sounds noticeably clearer and better than the others. YMMV, I guess

 
I've personally come to the conclusion that the ppl who sell $150 USB cables are crooks, that the $1 cables are junk...and that $5 will get you high purity copper, proper shielding and a good twisted pair yadayada..

 

[travisg]

Just found out that my Locus cables do make a difference. Stoked.

 

[IPodPJ]

Quote:

I've personally come to the conclusion that the ppl who sell $150 USB cables are crooks

Regardless of your opinion of how any cables sound, cables take time to build by hand.  People charge for their labor.