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USB cable and Sound Quality - Page 24  

post #346 of 783
Quote:
Originally Posted by Currawong View Post

 

What is lacking here in these discussions are specifics. I've seen this posted, in effect, numerous times, but no discussion or specifics about individual DACs and their capabilities. I also posted those links so that people who are interested in genuinely learning, not just arguing, might do some research. Beyond that, I'm not making any specific argument, just trying to direct the discussion to something beyond the regular arguments which don't benefit anyone.smile.gif

 

As I asked, is anyone interested in some actual measurements and experiments or only interested in arguing what they believe is correct

What measurement are we talking about here? Jitter of the cable or jitter of the USB port. I do not disagree jitter has a effect on sound quality (in measurement). I do disagree that an exotic silver USB cable will fix it. And I am not sure how much people can actually precieve jitter. I am an engineer. The engineering approach to this is first to identify the problem.

 

1. What does jitter sound like? I have seen any description of what jitter sounds like other than the cable sounds better, has more bass, has more detail. And we know it can not be true as cable can not modify 1 and 0 in a non-random manner.

2. If indeed, we found jitter is observable through normal listening. The jitter can be from the transmitter, cable or receiver. We can now try to identify the source of jitter. The jitter in the cable could be in fs and not even ps. From my experience, the jitter are sourced mostly from the transmit driver and not the cable.

post #347 of 783
Jitter in the levels it occurs in even the least expensive audio gear does not affect sound quality. Not audible.
post #348 of 783

dvw: Did you read Dan Lavry's posts? He wrote about the effects specifically.  I don't think "jitter has a sound", I think his point was that jitter can degrade the sound, but how much or how noticeably doesn't have simple figure of X picoseconds or X nanoseconds but is complex and depends on many factors.

 

Specifically regarding USB cables, manufacturers I have spoken to suggested that they need to have the correct characteristic impedance (just as any digital cable should). My feeling at the moment is, having played around with a bunch of combinations of cables, components and other things, is that they should be as short as possible as well, but that could be because the longer cables I've used all passed by other equipment and may have been picking up noise.

 

I really do wish I could test all of this, as I think it would be good to try and get some useful information that can be helpful to people, so I'll see if that can't be done. Just don't hold your breath, as I've got a bunch of other things I want to do as well. smile.gif

post #349 of 783
Quote:
Originally Posted by bigshot View Post

Jitter in the levels it occurs in even the least expensive audio gear does not affect sound quality. Not audible.

 

Strongly disagree, but I can see how this could quickly degenerate so I'll leave it there,  

post #350 of 783
Quote:
Originally Posted by bigshot View Post

Jitter in the levels it occurs in even the least expensive audio gear does not affect sound quality. Not audible.

 

I don't have any sources to cite or evidence, but I wouldn't be so sure of that, particularly if you phrase it as "audio gear."  Maybe we're thinking of different things?  Are you thinking on the level of cheap CD players, iDevices, etc.?  Or anything like a computer, phone, whatever would be used for music playback?  How about really junky integrated audio systems for those cards that play recorded messages, a GPS device, whatever?

 

But anyhow, I think the point is that nobody yet seems to have proved jitter audibility at levels close to that of modern low-end dedicated consumer playback gear.  That said, isn't it hard to adjust the amount of jitter at very low levels for testing?  It's not like you can compare device A with device B, since they will differ in a lot of other ways other than jitter.  Anyway, I won't discount a possibility, but it's not something I think is probably a big deal, given the levels we're talking about.  Then again, most audiophiles don't tend to care about things in the correct order of importance, so latching onto jitter doesn't seem like a surprise, regardless of the actual importance...

 

 

Quote:
Originally Posted by Currawong View Post

dvw: Did you read Dan Lavry's posts? He wrote about the effects specifically.  I don't think "jitter has a sound", I think his point was that jitter can degrade the sound, but how much or how noticeably doesn't have simple figure of X picoseconds or X nanoseconds but is complex and depends on many factors.

 

Specifically regarding USB cables, manufacturers I have spoken to suggested that they need to have the correct characteristic impedance (just as any digital cable should). My feeling at the moment is, having played around with a bunch of combinations of cables, components and other things, is that they should be as short as possible as well, but that could be because the longer cables I've used all passed by other equipment and may have been picking up noise.

 

I really do wish I could test all of this, as I think it would be good to try and get some useful information that can be helpful to people, so I'll see if that can't be done. Just don't hold your breath, as I've got a bunch of other things I want to do as well. smile.gif

 

 

The most important message from Dan Lavry and Michael Goodman (and what many people have been saying all along) is that jitter matters at the D/A conversion.  It doesn't matter what happens elsewhere as long as the jitter at the conversion is low enough.  This point seems to be ignored by many.

 

It's up to the D/A device designer to deal with whatever input signal comes in.  For all but the cheapest USB DAC implementations, I really don't see any substantive relationship between the jitter on the USB data transmission that the USB receiver chip sees and any jitter at the output of the DAC chip.

 

Or is everybody buying expensive USB cables for their $20 USB DAC that uses one of those low-end all-in-one USB receiver/DAC chips (one that actually uses its integrated DAC) that makes no attempt at cleaning anything up, getting better sound quality?  And even then, is it an audible concern?  Even if it's an audible concern, don't you have bigger issues to worry about with a $20 DAC?

 

That's even supposing it really matters, that for some reason you're focusing on the cable rather than the USB host and of course the device on the receiving end, that the differences between cheap and expensive cables (which ones?) really amount to something much.

 

I mean, hopefully people buy expensive DACs before expensive USB cables, and the expensive DACs already took care of the issue.  Oh wait, we're trusting audiophile gear to take care of anything properly, aren't we?  redface.gif


Edited by mikeaj - 8/29/12 at 8:37pm
post #351 of 783
We're talking about cd players and things to listen to music on. Why would I be talking about anything else?

I think we owe it to newbies to speak clearly and not go into supefluous detail. A lot of times people are so busy outlining the exceptions to the rule they give the impression that the baby has been thrown out with the bathwater. I can't think of a reason why we need to spend any more time discussing jitter except to say it's a non issue. That's the fact that we need to get across to newbies.
Edited by bigshot - 8/29/12 at 8:43pm
post #352 of 783
Quote:
Originally Posted by bigshot View Post

We're talking about cd players and things to listen to music on. Why would I be talking about anything else?

 

Dunno, just throwing stuff out.  I'm sure there are some extremely suspect audio devices used to listen to music that nobody's bothered to measure, but I think that's besides the main point since nobody worrying about these things is using their laptop (and I mean one of the worst laptops for audio, not something with relatively good integrated audio.  or what's worse than that?  some old phones?) directly as the source.

post #353 of 783
Quote:
Originally Posted by Currawong View Post

 

Specifically regarding USB cables, manufacturers I have spoken to suggested that they need to have the correct characteristic impedance (just as any digital cable should). My feeling at the moment is, having played around with a bunch of combinations of cables, components and other things, is that they should be as short as possible as well, but that could be because the longer cables I've used all passed by other equipment and may have been picking up noise.

 

Definitely +1 on the impedance issue. I have a usb to spdif converter with an aes/ebu output, and I tried to listen to it using a slightly better than average 3-pin XLR audio cable to connect that to my DAC's input. It was nothing you would want to listen to for too long. Then I got a digital cable with the correct impedance and everything was hunky-dory.

 

It does get mentioned from time to time that too short of a coax or usb cable can degenerate the signal as well. I have a 6" Belkin on the way to connect to a simple usb to spdif converter, we'll see if it's detrimental.

post #354 of 783

I think the possible issue with short cables is signal reflections, I think the idea with longer cables or ferrites is to attenuate the reflections/noise within the cable.  Like anything though this all depends on specifics so one would need to use an oscilloscope to study the cable to determine how much of a problem signal reflections are.  Signal reflections to my knowledge are caused by stray impedances, so this will probably vary with cable termination, connector type, in there is a hookup used inside the divice etc.

post #355 of 783

I can't wait to hear NAD's C390DD (the M2 is well above my budget) - taking the analog conversion completely out of the equation is an interesting prospect. Ironically, anyone needing to hook an analog source up to one of these amps now has to buy an optional MDC module. Ditch the DAC for an ADC and look forward to DSP updates further down the pike.Outstanding. biggrin.gif

post #356 of 783
Quote:
Originally Posted by Currawong View Post

dvw: Did you read Dan Lavry's posts? He wrote about the effects specifically.  I don't think "jitter has a sound", I think his point was that jitter can degrade the sound, but how much or how noticeably doesn't have simple figure of X picoseconds or X nanoseconds but is complex and depends on many factors.

 

Specifically regarding USB cables, manufacturers I have spoken to suggested that they need to have the correct characteristic impedance (just as any digital cable should). My feeling at the moment is, having played around with a bunch of combinations of cables, components and other things, is that they should be as short as possible as well, but that could be because the longer cables I've used all passed by other equipment and may have been picking up noise.

 

I really do wish I could test all of this, as I think it would be good to try and get some useful information that can be helpful to people, so I'll see if that can't be done. Just don't hold your breath, as I've got a bunch of other things I want to do as well. smile.gif

To be honest, I did not read Dan's paper in great depth because I did not find any new and insightful information. Not that I disrespect Dan, but I have been in the communication business for 20 years and jitter is a major issue for us to deal with. I am not a jitter expert but I know quite a few that are. The major difference between our work are in communication we're dealing with Kms of cables that often do not have great continuity. Meaning cables might be 24AWG for 500 meters and then 28AWG for the next 1.5 Km. So how much magic jitter can there be in 1 meter of USB cable. IMO, the majority of jitter is contributed by the PLL and not the cable. Here's an example paper. http://www.kenkundert.com/docs/aacd97.pdf This is a little too much for this forum.

 

My issue with the explanation that jitter in the cable are:

1. Description of the sound of jitter. I am not dealing with people's ability to hear jitter yet. No one has given a qualitative description of jitter. Degradation of audio is not a description. More bass/more treble is not a description. Jitter actually modulated the signal. For example, if you play an off center LP, part of the playing will be at a higher speed than the other part, this change the frequency of the signal. This is not an  accurate analogy of jitter but it is simple to use without getting into Fourier Transform.

2. Second issue I have is nobody has explained to me how is the play clock derived from the USB clock (source of jitter right?). If a recording is done with a 44.1KHz +/- 1 KHz clock, How does the USB know it is 43KHz and not 45KHz? What if there are two tracks streaming and one with 43KHz and one with 45KHz?

3. Let's ignore the difference in USB2.0 and 3.0 with regards to synchronizing them to the play clock. The jitter will be smaller in relation to the clock period of a slow USB than a fast USB. Does this mean you have better performance in USB1.1 than USB2.0? Why hasn't any DAC been touting that fact?

 

I think there are just so much disinformation out there to justify the extraordinary price of these cables. We just need to drill down on it. I'm surprised nobody is selling an ionizer to make the air more conductive so we get more detail when we're streaming music over WiFi.


Edited by dvw - 8/30/12 at 3:28pm
post #357 of 783
Quote:
Originally Posted by drez View Post

I think the possible issue with short cables is signal reflections, I think the idea with longer cables or ferrites is to attenuate the reflections/noise within the cable.  Like anything though this all depends on specifics so one would need to use an oscilloscope to study the cable to determine how much of a problem signal reflections are.  Signal reflections to my knowledge are caused by stray impedances, so this will probably vary with cable termination, connector type, in there is a hookup used inside the divice etc.

It's easier to damp the reflection with a small serial resistor. The drawback is you will be attenuating the signal. Too long a cable might have round trip delay issue.


Edited by dvw - 8/30/12 at 3:27pm
post #358 of 783
Quote:
Originally Posted by dvw View Post

 Jitter actually modulated the signal. For example, if you play an off center LP, part of the playing will be at a higher speed than the other part, this change the frequency of the signal. This is not an  accurate analogy of jitter but it is simple to use without getting into Fourier Transform.

 

And that begins to make sense for analogue audio signals. But not for digital. That would only cause a skew in the timing between the bits, but not their values (which would determine the frequencies) and the timing would - presumbably, be fixed in any re-clocking the transfer does.

post #359 of 783
Quote:
Originally Posted by liamstrain View Post

 

And that begins to make sense for analogue audio signals. But not for digital. That would only cause a skew in the timing between the bits, but not their values (which would determine the frequencies) and the timing would - presumbably, be fixed in any re-clocking the transfer does.

You are correct and that's why I stated it is not accurate Someone else has called me out on it before. Jitter does skew the timing and it does it by a certain frequency as well. The drift in timing goes back and forth. This is known as the jitter frequency. Without the back and forth action it will be just a drift in frequency (replay is simply slowed/speeded down). This jitter has a frequency and this frequency modulated the signal and generate two other frequencies. So in a way, instead of harmonic distortion it is a frequency distortion. I am not very good in explaining this. Someone else could give this a better shot, please do.

 

I used the off center LP as an analogy because as the turntable turns, the distant side (relative to the hole) will have a higher velocity and produce a higher pitch. The less distant side will have a lower pitch. As you point out this is not the same as digital timing skew, but I think it's good enough for simple understanding. Sorry for dumbing it down. But this is the best I can come up with.

 

What exactly does jitter sound like? I am not sure because I really never heard an identified jitter induced sound. But this is what I think it could sound like. If jitter is severe, it will miss bits and this will sound like a lot of pop. If the jitter frequency is high, it might be beyond human hearing. If it is low then, it could sound like a change in pitch. Of course, this is assuming, the jitter is large and uncorrected.

post #360 of 783
Jitter would affect higher frequencies first, I would imagine.
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