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post #5356 of 7925
Quote:
Originally Posted by wisemanja View Post

When you are talking about USB synchronous transfer, the problems are really all the same as the problems you get with S/PDIF protocols such as TOSlink, AES/EBU, or the digital coax interfaces. Asynchronous USB transport does get around some of these problems *If* your equipment has that capability. But consider the following:

 

The transfer of "ones and zeros" is an oversimplification of what physically must occur to convey data and typically is not understood by many. All information transfer is analog. Digital data is transferred in an analog format and therefore is still subject to some (although fewer) analog problems.

 

For example, on a wire that is sending a voltage between 0 and 5 volts, what voltage would constitute a "0"? 0 volts for sure but what about 0.1 volts or 0.2 volts? Noise does occur on digital lines. And what would be a "1"? Well 5.0 volts for sure but the further down the line you get, that signal degrades. If you saw a value of 0.5 volts, would you consider it a "0" or a "1"? Noise on the line can knock a signal up or down. And when do you look at the line to "read" the bit value? In the middle, the end, or the begining? How do you even know where any of these are when the waveform of the bit is distorted due to noise, cable length, and loss of required harmonics?

 

If a bit is knocked out or a block of bits is hit, most digital protocols have error correction and parity detection to deal with it. If a receiver gets a section of data that is marked as containing bad information, it can request the transmitter to re-send it. This allows computer data to be transferred with exact precision.

 

That is "computer data". Audio data is quite a different story. Audio data is all "real time". In general bits coming in must be EXACTLY in the time slot they are expected. Let's go back to the voltage on a wire discussion above.

 

In our example, when a bit stream is sent out on the wire, it is basically a stream of squared off waveforms (i.e., step functions) with a value of either 0 or 5 volts. A Fourier analysis of a step function shows that you have to have all of the odd harmonic frequencies of the base in order to keep the step function "sharp" (i.e., for the square wave to look like a square wave). If you start losing those harmonics, the square wave begins to distort into a rounded off waveform. Once that is gone it is hard to know where the "beginning" of the bit is. So here's a little math:

 

If you are transferring a 24/196kHz audio file over a digital cable, that is a total bit frequency of 24 * 196kHz = 4.7 megabits per second. In order to maintain a decent signal waveform lets limit the number of odd harmonics to support to about 5. This takes you to the 11th harmonic of 4.7 mHz which is around 52mHz. Your cable has to pass 52mHz just to maintain the bulk of the waveform. If you are trying to transfer computer data, this is not necessary. Even if the waveform is totally rounded off by losses in the cable, the computer just looks for the middle of the bit's signal to determine if it is a "0" or "1" and if it reads wrong, it uses error correction techniques to fix it. A normal 12mHz USB cable would be sufficient for that computer data.

 

However, since audio data is real time, you can't be requesting re-transmission of data (no time to do it) when hits occur so the cable needs to be uber-shielded and the DAC has to have some other scheme to eliminate bit erros. Also using the 12mHz USB cable you barely get the first odd harmonic (4.7mHz * 3 = 14.1mHz) of the 5 that you need for prober bit positioning. Since the re-clocking of data is based on when the bits are detected, and since each bit is significantly rounded off and distorted without those odd harmonics, the clock has to continually re-adjust when the bits are fed into the DAC for conversion. This constant jumping around of the clock positioning of bits is called jitter and the effects of jitter in the data conversion can be heard, especially on highly resolving amps and transducers.

 

So in summary, even though the USB standard can be used for errorless data transfer of computer data (assuming that proper error checking and correction is used), under many circumstances USB cables with a much higher bandwidth and noise rejection than that required by the USB standard will improve audio data transfer (less jitter) and reduce data hits (less noise). How much of those benefits that you see on your system is dependent on many other issues, of course.

where do you get this info from? this stuff is golden and not the kind of thing that comes with user manuals. do you work in the industry?

post #5357 of 7925
Quote:
Originally Posted by vlach View Post


+1, i fully agree. This can also be proven on a spectrum analyzer. Take ANY two USB cables and compare the output signal fed from the same signal on a spectrum analyzer and you will not be able to discern any difference. Snake oil. Oh...and WWF wrestling is also fake btw.

Not sure what exactly you were measuring when you tried this, but frequency response doesn't show much. The phase coherency of all step functions must be maintained across the cable (i.e., the high frequency stuff gotta get to the end at exactly the same time as the low so that square waves in come out as square waves.

 

What you need to do is to produce some eye-charts from the measurements that will show the jitter parameters on audiophile sample rates. I suspect that you will then be able to discern some differences.

 

Oh...and WWF couldn't possibly be fake! Can't you see how much pain those guys are in when they've been slammed? eek.gif

post #5358 of 7925
Quote:
Originally Posted by magiccabbage View Post

where do you get this info from? this stuff is golden and not the kind of thing that comes with user manuals. do you work in the industry?

+1
post #5359 of 7925
Quote:
Originally Posted by magiccabbage View Post

where do you get this info from? this stuff is golden and not the kind of thing that comes with user manuals. do you work in the industry?

I have been an engineer since I was 9 and built my first crystal radio smile.gif Technology has always been a great interest of mine. I have a diploma of technology in Telecommunication and Navigational electronics from BC Institute of Technology, and a degree in Mathematics/computer science and I worked in Telecommunication systems engineering specifically (including high bandwidth digital over optics) for well over 26 years.

 

I also spent 6 or 7 years really involved in Audio. Since like most folks, I didn't have much "extra" money (4 kids in school, mortgage, you know the story) I had to do a lot of exploring in order to put together a system that I really liked. I did a lot of experimenting with my own design of cables and subsequent long listening sessions to tell the differences.

 

In fact it's always been fun when I've found some strange behavior (usually with cables) and I go tell one of my engineering friends about it and he's like, "that ain't possible because.....". Then I get him over and set him down to listen for a while and then I say, "why is that happening since it ain't possible?" and he goes, "well, gee..., let's hear that again". Heh!

 

Yea, I've been interested in why what the engineers (and my own training) would say,"that shouldn't be happening" and so my curiousity has driven me a bit further and I've discovered that there is usually extra information that has not been considered. The mis-direction bit is pretty common too. You're looking a a part that you've changed out when the real item causing a particular behavior is down the chain somewhere. Also, it's important to know that Audio "snake oil" is kinda like myths. There is usually some fact that existed that the "myth" was based on. I have found that pursuing those items has frequently been enlightening.

 

In 2001 when the Telecom industry shut down, I wasn't gainfully employed for nearly 4 years. Had to sell nearly all of my audio equipment to pay bills. Since a lot of the stuff we had left (e.g., car radio, simple stereo receiver, cheap speakers) were so poor to listen to, I basically stopped listening. About 4 months ago I bought my T1 and HDVD800 and have been loving my music again.

 

Because I've always loved hearing others experiences with their music and equipment, I have ASSUMED that others on this forum might enjoy these thoughts, so I tend to share a lot smile.gif It's really just another aspect of my hobby -- Technical interest, music enjoyment, and talking about it with others.

post #5360 of 7925
Quote:
Originally Posted by wisemanja View Post

I have been an engineer since I was 9 and built my first crystal radio smile.gif Technology has always been a great interest of mine. I have a diploma of technology in Telecommunication and Navigational electronics from BC Institute of Technology, and a degree in Mathematics/computer science and I worked in Telecommunication systems engineering specifically (including high bandwidth digital over optics) for well over 26 years.

 

I also spent 6 or 7 years really involved in Audio. Since like most folks, I didn't have much "extra" money (4 kids in school, mortgage, you know the story) I had to do a lot of exploring in order to put together a system that I really liked. I did a lot of experimenting with my own design of cables and subsequent long listening sessions to tell the differences.

 

In fact it's always been fun when I've found some strange behavior (usually with cables) and I go tell one of my engineering friends about it and he's like, "that ain't possible because.....". Then I get him over and set him down to listen for a while and then I say, "why is that happening since it ain't possible?" and he goes, "well, gee..., let's hear that again". Heh!

 

Yea, I've been interested in why what the engineers (and my own training) would say,"that shouldn't be happening" and so my curiousity has driven me a bit further and I've discovered that there is usually extra information that has not been considered. The mis-direction bit is pretty common too. You're looking a a part that you've changed out when the real item causing a particular behavior is down the chain somewhere. Also, it's important to know that Audio "snake oil" is kinda like myths. There is usually some fact that existed that the "myth" was based on. I have found that pursuing those items has frequently been enlightening.

 

In 2001 when the Telecom industry shut down, I wasn't gainfully employed for nearly 4 years. Had to sell nearly all of my audio equipment to pay bills. Since a lot of the stuff we had left (e.g., car radio, simple stereo receiver, cheap speakers) were so poor to listen to, I basically stopped listening. About 4 months ago I bought my T1 and HDVD800 and have been loving my music again.

 

Because I've always loved hearing others experiences with their music and equipment, I have ASSUMED that others on this forum might enjoy these thoughts, so I tend to share a lot smile.gif It's really just another aspect of my hobby -- Technical interest, music enjoyment, and talking about it with others.

This post explains a lot. Thanks for sharing. You seem to have more insight than most of the people who post here so it is always really interesting to read your posts. I heard the HD800 today for the first time . I had my WA2 and T1 there as well for comparisons. I have decided that I cant live without owning both headphones so I will get the HD800 also. 

 

You mentioned hat you studied mathematics, I finished a book about Piere De Fermat not too long ago. It was the best non-fiction I have ever read. A very inspiring book indeed. Some of the ideas in the book were hard to comprehend but in the end it was very rewarding. 

post #5361 of 7925
Quote:
Originally Posted by magiccabbage View Post
 

This post explains a lot. Thanks for sharing. You seem to have more insight than most of the people who post here so it is always really interesting to read your posts. I heard the HD800 today for the first time . I had my WA2 and T1 there as well for comparisons. I have decided that I cant live without owning both headphones so I will get the HD800 also. 

Thanks, 

 

As long as folks find my ramblings of interest, I will likely continue. I've been unemployed for a while and so it has allowed be time to embellish on a lot of this :smile: I also remember days in my youth when I had all sorts of questions about radio stuff and audio but no-one in my part of the country had any answers for me (and of course we didn't have the internet yet) so it was always great to find folks who at least had some experience they could relate.

 

Your experience with the HD800 worries me. I've been thinking that I'd like to listen to some on the HDVD800 that I have, but I have no real money at the moment so I'm thinking I better stay away...:rolleyes:

post #5362 of 7925
Quote:
Originally Posted by wisemanja View Post
 

Thanks, 

 

As long as folks find my ramblings of interest, I will likely continue. I've been unemployed for a while and so it has allowed be time to embellish on a lot of this :smile: I also remember days in my youth when I had all sorts of questions about radio stuff and audio but no-one in my part of the country had any answers for me (and of course we didn't have the internet yet) so it was always great to find folks who at least had some experience they could relate.

 

Your experience with the HD800 worries me. I've been thinking that I'd like to listen to some on the HDVD800 that I have, but I have no real money at the moment so I'm thinking I better stay away...:rolleyes:

I for one greatly enjoy your "ramblings".....in spite of myself I might have learned something....

post #5363 of 7925
Quote:
Originally Posted by philo50 View Post
 

I for one greatly enjoy your "ramblings".....in spite of myself I might have learned something....

Well Thanks!

 

I think that you were someone who not too long ago made a reference to the effect that "you guys have probably forgotten more than I know."

 

Well you may have no idea of how much I've forgotten. Now days if I want to be credible, I usually have to go look up stuff that I used to be able to quote off the cuff. My brain is going but at least my ears are still holding out :beyersmile:

post #5364 of 7925
Quote:
Originally Posted by wisemanja View Post
 

Thanks, 

 

As long as folks find my ramblings of interest, I will likely continue. I've been unemployed for a while and so it has allowed be time to embellish on a lot of this :smile: I also remember days in my youth when I had all sorts of questions about radio stuff and audio but no-one in my part of the country had any answers for me (and of course we didn't have the internet yet) so it was always great to find folks who at least had some experience they could relate.

 

Your experience with the HD800 worries me. I've been thinking that I'd like to listen to some on the HDVD800 that I have, but I have no real money at the moment so I'm thinking I better stay away...:rolleyes:

To be honest I didn't think I would like the HD800 that much, I was kind of expecting to be let down. It blew me away. I was shocked by how good it sounded. Also it was brand new, the guy in the store said it had less than 5 hours on it. 

 

I'm gonna get to hear the HVD800 soon as well, also will be going to the Sennheiser factory here in Ireland, I'm looking forward to that. 

post #5365 of 7925
Quote:
Originally Posted by philo50 View Post
 

I for one greatly enjoy your "ramblings".....in spite of myself I might have learned something....

+1.  Great to read stuff like that.

post #5366 of 7925
Quote:
Originally Posted by wisemanja View Post
 

When you are talking about USB synchronous transfer, the problems are really all the same as the problems you get with S/PDIF protocols such as TOSlink, AES/EBU, or the digital coax interfaces. Asynchronous USB transport does get around some of these problems *If* your equipment has that capability. But consider the following:

 

The transfer of "ones and zeros" is an oversimplification of what physically must occur to convey data and typically is not understood by many. All information transfer is analog. Digital data is transferred in an analog format and therefore is still subject to some (although fewer) analog problems.

 

.............

If a bit is knocked out or a block of bits is hit, most digital protocols have error correction and parity detection to deal with it. If a receiver gets a section of data that is marked as containing bad information, it can request the transmitter to re-send it. This allows computer data to be transferred with exact precision.

 

That is "computer data". Audio data is quite a different story. Audio data is all "real time". In general bits coming in must be EXACTLY in the time slot they are expected. Let's go back to the voltage on a wire discussion above.

 

...............................

 

Bolded section ..... not really.  These blocks of data are error corrected and buffered and reclocked at the receiving end.  This is why I am skeptical about USB cable claims.  The only possible explanation I could possibly entertain is that a better shielded cable might leak less EFI into the receiving electronics, messing with the output of the DAC.

 

I haven't heard any difference in SQ between the included USB out from my Conductor and the optical cable, which leaves me skeptical.  A lot of folks swear "they have heard the difference", so far be it for me to doubt them... I only ask what is the explanation of the phenomenon?

post #5367 of 7925
Quote:
Originally Posted by BobJS View Post
 

 

Bolded section ..... not really.  These blocks of data are error corrected and buffered and reclocked at the receiving end.  This is why I am skeptical about USB cable claims.  The only possible explanation I could possibly entertain is that a better shielded cable might leak less EFI into the receiving electronics, messing with the output of the DAC.

 

I haven't heard any difference in SQ between the included USB out from my Conductor and the optical cable, which leaves me skeptical.  A lot of folks swear "they have heard the difference", so far be it for me to doubt them... I only ask what is the explanation of the phenomenon?

 

Dost thou DARE dispute the WiseManga!!!!

post #5368 of 7925

Hi WiseManja,

 

I like to read your explanation, I'm learning a lot, but on the XLR (Balanced part) there is one thing that I don't understand, how there could be an impact even if there is some noise going into the cable since basically the way I understand it, there is 2 opposed polarity, so the transformer at the end and subtract what was added during the transport. Wikipedia explain it better then me:

 

Quote:

A typical balanced cable contains two identical wires, which are twisted together and then wrapped with a third conductor (foil or braid) that acts as a shield. The two wires form a circuit carrying the audio signal; one wire is in phase with respect to the source signal, the other wire is reversed in polarity, which is also referred to as being 180° out of phase at all frequencies. The in-phase wire is called non-inverting, positive or "hot" while the out-of-phase wire is called inverting, phase-inverted, anti-phase, negative or "cold". The hot and cold connections are often shown as In+ and In− ("in plus" and "in minus") on circuit diagrams.[1]

 
 

The term "balanced" comes from the method of connecting each wire to identical impedances at source and load. This means that much of the electromagnetic interference will induce an equal noise voltage in each wire. Since the amplifier at the far end measures the difference in voltage between the two signal lines, noise that is identical on both wires is rejected. The noise received in the second, inverted line is applied against the first, upright signal, and cancels it out when the two signals are subtracted.

 

My DAC and my amp are connected with 2 x 3 pin XLR cable (one for left and one for right) I'm currently using short 3ft Digiflex professional with neutrik connector.

 

My T1 really sing on my setup, I can't stop listening to music, I have discovered the "lossless" and "HD" track, I enjoy it big time.

 

As for the USB cable, I use a cheap 10ft $3 Startech cable with little to no shielding to connect my DAC and it works well. My usb cable go behind my desk and follow I don't know how many other 120volts wires and I don't hear any noise if a track if perfectly silent even if I set my auditor to the maximum (which would blow my headphone if any sound were played).

post #5369 of 7925
Quote:
Originally Posted by BobJS View Post
 

 

Bolded section ..... not really.  These blocks of data are error corrected and buffered and reclocked at the receiving end.  This is why I am skeptical about USB cable claims.  The only possible explanation I could possibly entertain is that a better shielded cable might leak less EFI into the receiving electronics, messing with the output of the DAC.

 

I haven't heard any difference in SQ between the included USB out from my Conductor and the optical cable, which leaves me skeptical.  A lot of folks swear "they have heard the difference", so far be it for me to doubt them... I only ask what is the explanation of the phenomenon?

Hi there. Thanks for the feedback.

 

Are you familiar with the framing for the synchronous USB protocol at all? I am not and so I can only surmise at the moment what error correction is done. I do know though, for standard S/PDIF transfers, the transmission has to basically be close to the audio sample rate so that it is easy to reconstruct the clock. For bit specific error recovery algorithm, you normally need a whole lot of redundant data, sorta like in the case of Cyclic redundancy checks (CRC) or Bose - Chaudhuri - Hocquenghem (BCH) type code. The extra data can add as much as 20% to 30% or more to the data overhead. I thought that this is the reason those codes are only used for computer data transfers. I do not believe that you can synchronously generate a bitstream and then receive and convert it using the transmit clock as the intended data conversion clock if you've added a pile of error correcting overhead on top. I know that the received data is buffered during the receive process and then reclocked, usually from a phase locked loop, but that loop ultimately is phase locked to some extent to the incoming data bit frequency. If you are sending all kinds of redundancy bits, how is the recovered clock going to remain in sync with the true data rate? My understanding is that Audio data is transferred in a fairly simple format for this reason and the idea is to just have the data transfer and clock recovery sooooo good that bits aren't being dropped.

 

The phase lock loops (PLLs) that are used for the reclocking are constantly trying to find where the "middle" of the bits are located and in general does help eliminate some jitter but not all. Since the PLLs are free running, they can wander over time. Any clarification that you could throw on this picture would be nice as I've never gotten down to the bit allocation level in my readings over the years. 

 

By the way, in recent years there have been some pretty clever ways to reduce jitter, but the best for USB is to just not use data with jitter in it. This is what the asynchronous mode transfer for USB is apparently about. You say that you are using the Conductor? Well from my reading, that beastie has a great DAC in it, and furthermore, it runs asynchronous on USB. My experience is that you wouldn't normally find that component digital cable sensitive. So far in my own experience, I have not seen cable related jitter problems with async USB. However, I have seen it on synchronous protocols such as the S/PDIF protocols. Frequently it was when using coax connection where ground loop noise rides on the sheild and screws up the symmetry of the data going to the DAC. I have not specifically seen it relative to synchronous mode transfer on USB, but since USB is more complicated to synchronously operate (i.e., its normal cable rate is not a clean multiple/submultiple of normal audio sample rates), I would think that it could be as cable sensitive as S/PDIF or AES/EBU and maybe even more so.

 

Your final question of "what is the explanation of the phenomenon?" relative to your Conductor and USB cables, I can't answer for asynch transfer because I've never seen it and I'm not sure I believe it. Are you saying that folks claim to have heard differences on the Conductor using different USB cables? That sounds a little odd to me. I wonder if they have their sources configured to use async. If not, that might contribute to an issue. Not sure what to say about that one.

post #5370 of 7925
Quote:
Originally Posted by Focker View Post
 

 

Dost thou DARE dispute the WiseManga!!!!

 Oh, PLEASE DO!

 

If I continue to ramble on and make mistakes in the process that are not challenged, then I get over confident and do dumb things. When I do dumb things, my wife corrects me and I'm embarrassed. I love my wife! But I would rather folks correct me so that I can learn instead of being embarrassed. :p

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