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Author Topic: a £400 digital interconnect  (Read 22999 times)

iain

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a £400 digital interconnect
« on: July 23, 2006, 07:58:52 PM »

This is a quick question for Dan lavry or anyone else with an opinion, I know you've all been asked this type of question if not this question every day for 10 years, so ill write every thing I think I know, and hope fully give you a yes no answer to make.

I study acoustics (results based on science tests and figures), and work in a hifi shop (results based on listening and opinion), and so always find myself stuck between a rock and a hard place when discussing the merit of audio equipment.

I am currently debating with a work college whether a
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Barry Hufker

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Re: a £400 digital interconnect
« Reply #1 on: July 23, 2006, 11:29:21 PM »

Iain,

You'll get better postings from people other than myself but I do want to jump in.

24 bits only equals a dynamic range of 144dB in theory and not in practice -- at least not at this stage of digital reality.  I am confident the DAC itself and the analog components have much more of an effect on sound quality than an expensive wire.

From a testing standpoint you're at a stalemate.  He says the wire makes the sound better.  You question that.  There has to be at least a third party to join one side or the other.  But more importantly, could your friend tell the difference if he didn't know whether the wire is in the circuit or not.

As long as the digital information travels the length of the wire intact, there is no way to improve the digital information no matter what wire is used.

If I paid 400 GBP for a wire I'd sure as hell tell you I heard a big difference whether I did or not.  No one wants to appear a fool.

Barry
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Scrith

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Re: a £400 digital interconnect
« Reply #2 on: July 24, 2006, 12:03:40 AM »

Can a blind test be arranged?  Many transports include at least two outputs (coax and toslink, for example), and most DACs have at least two inputs with a switch in front to pick which one is in use, making comparisons really convenient.

I've done this a number of times to compare coax vs. toslink in my setup.  At one point I think I had a really bad toslink cable (one of the eBay glass toslink cables that many people claim is a bargain) and I could actually tell the difference between them (with my wife switching the input randomly on my DAC).  But after purchasing a reasonably priced replacement (Van den Hul Optocoupler) I can't tell the difference between them anymore.  I have some suspicions that something can happen to that glass fiber (micro-fractures or something?) that leads me to distrust toslink, but I'm fairly certain it would be difficult to hear the difference between coax cables.

By the way, I'm generally a skeptic of blind tests, based on my own experience.  I've done some careful tests on my own to try to tell the difference between two cables, only to have them end up sounding the same.  So then I start using a new cable...and a few days later I hear something different in some random piece of music.  I then pick up the blind-testing again using that music, and can sometimes hear the difference, at last.  Is a slight difference I can only hear every few days worth an expensive cable?  I'm not sure...  I also wonder if there is some sort of subliminal audio information in there that isn't so obvious (and can't be detected reliably in a blind test), but actually makes you feel differently about music over a long listening period.  I'm sure somebody has something a lot more detailed to say about this type of thing.  I'm also sure there are cable skeptics out there who confidently dismiss such ideas.  I maintain an agnostic position on cables for now.
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Gunnar Hellquist

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Re: a £400 digital interconnect
« Reply #3 on: July 24, 2006, 05:53:01 AM »

Iain,
    I think you either has to believe in the difference or change job.

Personally, I am firmly convinced that good enough is what it takes for digital signals. Any more than good enough is not adding anything from an engineering standpoint. Less than good enough and you most often get very recognizable errors. There can be quite a number of different criteria for this -- on an optical interconnect signal damping is of course important. Mechanical stability, resiliance to fire or oils might be other factors, mostly not relevant to a typical home setup. Personally I use the
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iain

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Re: a £400 digital interconnect
« Reply #4 on: July 24, 2006, 09:12:59 PM »

Hi Barry, he as yet hasn’t paid for it, thats the liberty we have as hifi shop employees we test stuff to death before we buy it, but after testing to death he’s still considering buying it (although at trade not quite as bad).      

With regards to Scrith’s comment when I blind test it, and test able to see the cable I can’t hear what I would describe as a marginal difference, and I’ve tested my ears in anechoic conditions I was able to blind test identify a level change of  1.5 db + my hearing still goes up to 16.5 kHz.  I shall continue to listen with more DAC’s, more amps, & more CD players and see if I can hear anything ill let you know if I do.

With regards to Gunnar im defiantly in the believer camp I believe that music reproduction is still a long way from being truly realistic even on 10k systems, But I don’t think throwing money randomly at parts of the system is going to help. I think we need more standardization as I say, is there not enough members of the AES on the web board alone to forward some kind of motion.

i.e.

Measurements are in two categories – AES test and Manufacturer test

For test can we not concoct a particular test and set of  measurements that would adequately demonstrate the performance of a DAC for example, we certainly have measurement mics at my uni that, shock horror are more sensitive than the human ear. I’m no expert in electronics but I imagine it is possible to measure changes of 0.0000001volts the voltage equivalent of the quietest thing we can hear. People may then say well a sine tone and pink noise are not music, they have no transients, no dynamic range, so create a peace of music that has the maximum possible dynamic range, frequency content ect and test and analyse that.  There’s, signal in, and signal out, any changes are a result of the DAC, im sure the modern FFT & distortion analysis is up to the task. From this derive say 4 AES measurements i.e.
Averaged A-weighted THD
Averaged A-weighted Signal to Noise
Averaged A-weighted Channel separation
Averaged frequency response variation

(or what ever else the AES members feel is necessary)

(I say A weighted as the A weighting curve is a reasonable middle ground and has been shown in the acoustics field to best represent peoples average perception of loudness and hence optimising to this should yield the best apparent audio reproduction I think .)

So every ones test spec pages look something like this
AES measurements

Averaged A-weighted THD
Averaged A-weighted Signal to Noise
Averaged A-weighted Channel separation
Averaged frequency response variation


Then the AES provides clear guide lines on the test procedure, and these figures should be able to be replicated by testing the relevant peace off kit by any company or lab that has the facilities, If your competitor is making suspect clams about his kit, test it and make sure every one knows there false. 20 companies come forward and say those figures are wrong, im sure the public will know who to believe.      

+ specify AES Cable resistances lengths ect (which hopefully everyone’s agreed on optimum)
If your kit needs special cable specify it, or provide it, don’t let the consumer be coned by other companies, who frankly haven’t earned his money.

Then 'Manufacturer test' can contain whatever condition the manufacturer likes i.e.  

ZHR weighted THD + signal reduction factor@1db gain of 63 = 0.000000000000001dB

With test standardization would we not drive manufacturers to produce better equipment not better marketing.

As to my job I would like kit that I can say and know will give the customer a good and functional product, yes someone may be happy with the idea his 10k system has improved but he’d feel a lot better and so would I if it actually did.

Thanks for all the feed back everyone, I think ill rephrase my question to Dan

What would be the Approx manufacturing cost of a 2 meter digital cable that you feel would allow the DA 924 to operate at its optimum capacity.

p.s i took this picture in scotland at the weekend


index.php/fa/3173/0/
Cheers
Iain
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Barry Hufker

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Re: a £400 digital interconnect
« Reply #5 on: July 25, 2006, 01:38:38 AM »

Toslink is a different question.  That's pretty much junk.  The telephone company does that technology correctly -- very high grade optical glass and high quality transmitter/receivers.  Toslink "optical fiber" tends to be extremely cheap plastic with a lot of "loss" -- poor light transmission down the fiber.  I would expect real problems there before any system with a good quality wire.

http://www.gotham.ch


GAC-1 S/PDIF-Pro (10070) Silvercable -- 1.85 Euros per meter or 146.5 Euros per 100 meter spool.

Barry
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blue2blue

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Re: a £400 digital interconnect
« Reply #6 on: July 25, 2006, 02:49:07 AM »

There are some folks  who seem to think that digital audio systems are always scudding along the brink of audio disaster, beset by torrents of uncorrected transmission errors that continually degrade the signal  resulting in all kinds of psychoascoustic nastiness.

I just don't think that's the case.

The job we ask of the digital part of the digital audio equation (in between AD and DA, as it were) is pretty straightforward and is not exactly a novel technical art.

It's easy to test transmission accuracy and that's how we've determined our standards for various interconnects. Those standards are not based around outside performance limits or best-of performances but rather are developed extremely conservatively to assure maximum accuracy.

There are so many places where we have to accept ambiguity and even mystery in audio (at least in the short term) but I just don't think the performance characteristics of digital cabling is one of those places.
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Gunnar Hellquist

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Re: a £400 digital interconnect
« Reply #7 on: July 25, 2006, 06:22:27 PM »

Hi again Iain.

Seems like you are willing to talk to the sceptictal people. Sorry if I destroy some beliefs. My suggestion though is to not use this kind of talk with your collegue, it will all only end up as a mess.

Your original question was something like this:
> How can a
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trevord

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Re: a £400 digital interconnect
« Reply #8 on: July 26, 2006, 02:58:20 PM »

Just to chime in..
I go with - no damn difference!! (to be subtle)
Gunnar says it best.
A point on jitter.
Jitter is important in ADC and low latency DAC.
Low latency DAC is used mainly by professionals where you turn a knob and want to hear a difference immediately.
Most consumer digital applications have enough buffering before/after cable transfer so that digital cable induced jitter (unless its so bad it destroys the data) does not have much of an effect.
Of course there is a lower limit to the type of consumer app I am talking about.
Who knows what the really cheap crap is doing Smile

Once a cable meets specs, you can't get better.

There may be a justification for cost tho.
A typical cheap digital cable is built from spec'ed components which have variation in quality.
A low cost manufacturer will assemble and assume since it was built from spec'ed parts - then it is in spec. Of course cheap materials for cheap cables will mean they have a variance (lets say 20% for each component) which means the final product will have a lot of quality variation.
Maybe no testing is done after the cable is built.

A reasonably priced cable will be built from materials with 10%  variance in parameters.
A sample of cables is taken from every batch to test to make sure they are in spec.

The most expensive cables (justifiably) will be built from materials with 5% or less (number are relative only - don't quote)
BUT
if the manufacturer tests each and every cable - the cost would be astronomical (relative to the cheapo).

The same may apply to the same brand - that is a manufacturer may  build with cheap materials and test 50% of them. Those which meet spec are the high priced versions , the others are put back in the "bin" with the rest.

So there is some variation in price. But not because a cable is "better" - a price increase may only mean - every cable of a particular brand meets spec. A lower cost may mean 40% or more of a particular cable is out of spec and you take your chances.

I am not saying this is a bad thing. You get what you pay for.
But you can't get better than the specification.
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Barry Hufker

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Re: a £400 digital interconnect
« Reply #9 on: July 27, 2006, 10:44:10 AM »

Let me just qualify one of the last statements -- you may get what you pay for.

Barry
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ssltech

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Re: a £400 digital interconnect
« Reply #10 on: July 31, 2006, 02:12:41 PM »

A wise man once answered a similar question in the following way; repeated here with the (paraphrased) question first:

Q] -Surely it's not possible to hear the difference between a $400 digital interconnect at my local hi-fi store and a $10 digital interconnect at the same hi-fi store?
A] -You CAN hear a difference, but only if you stand the side of the counter where the cash drawer opens towards you.

Depends what you're comparing it to. I personally reckon I can detect the difference between an expensive interconnect and a short length of twisted wet string, but as soon as the wet string is replaced by something which passes the data in a manner which allows the words to be reconstructed reliably (which costs all of about $5...) then I cease to be able to hear the difference.

Keith
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MDM (maxdimario) wrote on Fri, 16 November 2007 21:36

I have the feeling that I have more experience in my little finger than you do in your whole body about audio electronics..

maikol

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Re: a £400 digital interconnect
« Reply #11 on: July 31, 2006, 05:47:59 PM »

I think trevor has a point here in the "why can it be so expensive?"


I once read all i could on "Transparent cable" 's (could be the maker of that 400GBP digital cable BTW?) website, and on Shunyata's too, just trying to see if their was some real technical info.

I have not found any, of course, but i saw that their most expensive cables each need several hours to be done (at least it's what they say!).

If that is true, then here is a big part of the answer considering the price.

I would compare that to buying a watch. You can buy a cheap quartz chinese watch for a few bucks, or you can buy a Patek Philippe, Breguet or whatever for several thousands. Both will give you what a watch is made for. The several thousands one will never be more precise than the cheap one (if not less because it might be mechanical!), but if you buy it, you are probably looking for more than just accurate time info...

And if you have such a beauty at your arm, you'll certainly have to have an expensive car too, and an expensive hifi system, and... you name it... Smile

This is just a part of the luxury business!

And oh! BTW i'm one of those who believe there are differences
Very Happy

well maybe not between digital cables!

Michael
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iain

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Re: a £400 digital interconnect
« Reply #12 on: July 31, 2006, 08:22:53 PM »

Again Thank you all for the feed back

An update on the cables my fellow staff member asked the area manager (next in line to him is the managing director owner of the company) today why digital cables made a difference and then made me explain what I was saying to him (the area manager), that was kind of awkward, but anyway what I eventually got him to admit (although I probably get a wage cut now) was that a modern well designed dac should not be improved by expensive digital cable, we then had a test with a (im going to mention names but only in positive light this in my opinion is all very good equipment and worth every penny)  2k musical fidelity dac, + a 3k denson transport + a 3k musical fidelity pre and power + 2k dynaudio speakers, 10k all in we’ve got more expensive stuff but we like the sound of  this lot. We tried digital coax from
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Barry Hufker

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Re: a £400 digital interconnect
« Reply #13 on: August 01, 2006, 12:29:03 AM »

If I answer correctly to any of the above do I get a 400 GBP interconnect?

Barry
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Gunnar Hellquist

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Re: a £400 digital interconnect
« Reply #14 on: August 01, 2006, 06:34:49 AM »

Hi Iain,
sorry about the wage cut. But I did try to warn you.

Gunnar
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Ronny

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Re: a £400 digital interconnect
« Reply #15 on: August 01, 2006, 08:50:31 AM »

blue2blue wrote on Tue, 25 July 2006 02:49

There are some folks  who seem to think that digital audio systems are always scudding along the brink of audio disaster, beset by torrents of uncorrected transmission errors that continually degrade the signal  resulting in all kinds of psychoascoustic nastiness.

I just don't think that's the case.

The job we ask of the digital part of the digital audio equation (in between AD and DA, as it were) is pretty straightforward and is not exactly a novel technical art.

It's easy to test transmission accuracy and that's how we've determined our standards for various interconnects. Those standards are not based around outside performance limits or best-of performances but rather are developed extremely conservatively to assure maximum accuracy.

There are so many places where we have to accept ambiguity and even mystery in audio (at least in the short term) but I just don't think the performance characteristics of digital cabling is one of those places.


This post is spot on. The biggest problem that I see with the "reported" cable differences is that people aren't confirming what they think their ears are telling them, with the scientific testing. Sighted testing is the first mistake in an audible test. The ear is a great device, the auditory cortex' ability to consistently relay that information to the brain and the brains ability to recall information from memory, 100% exact everytime, is not so hot and that's the real problem and why there are so many different opinions regarding the sonic qualities of cable brands. In the US you have ANSI specifications and electronic codes. These are always overkill, so when you meet the requirement, for example the proper AWG for length of cable run to a speaker, if you go over that, there is no sonic improvement, the specs are already designed for overkill.  
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------Ronny Morris - Digitak Mastering------
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----------Powered By Experience-------------
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Bubblepuppy

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Re: a £400 digital interconnect
« Reply #16 on: August 26, 2006, 03:55:27 PM »

"the specs are already designed for overkill"
That's just not correct, let me take a constantly used standard and reveal its dirty little secret.
Cat5/Cat5E/Cat6/ And now 6A (10gig)
The specs are all referenced in the LAB at 20C (68-72F).

The effect of ambient temperature on cable attenuation was not addressed until several years later by whats known as characterization, suggested margin above the standard.
The standard does not force the obviously needed margin, so meeting the standard is minimum compliance, far from overkill.
The standard bodies are not, I repeat, not run by engineers, they are driven by economical feasibility.
A note on fiber, the "water peak" issue has only recently seen improvement.
Glass is not just glass, If your using a led x-mitter the best data rate you can achieve is @ 800mbps.
Led technology will not fire fast enough to provide 1000BaseT or beyond, enter the VCSEL technology which uses DWDM/CWDM/WDM

The Pro audio industry digital standards are still in the dark ages.
Unless there is a OC192 communication AES standard i missed.
Also the new cat6A utp standard supports 10gig Ethernet,but all cable is not made equal.
Physicals=electricals

Good day



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danlavry

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Re: a ?400 digital interconnect
« Reply #17 on: August 30, 2006, 03:27:22 PM »

Bubblepuppy wrote on Sat, 26 August 2006 20:55

"the specs are already designed for overkill"
That's just not correct, let me take a constantly used standard and reveal its dirty little secret.
Cat5/Cat5E/Cat6/ And now 6A (10gig)
The specs are all referenced in the LAB at 20C (68-72F).

The effect of ambient temperature on cable attenuation was not addressed until several years later by whats known as characterization, suggested margin above the standard.
The standard does not force the obviously needed margin, so meeting the standard is minimum compliance, far from overkill.
The standard bodies are not, I repeat, not run by engineers, they are driven by economical feasibility.
A note on fiber, the "water peak" issue has only recently seen improvement.
Glass is not just glass, If your using a led x-mitter the best data rate you can achieve is @ 800mbps.
Led technology will not fire fast enough to provide 1000BaseT or beyond, enter the VCSEL technology which uses DWDM/CWDM/WDM

The Pro audio industry digital standards are still in the dark ages.
Unless there is a OC192 communication AES standard i missed.
Also the new cat6A utp standard supports 10gig Ethernet,but all cable is not made equal.
Physicals=electricals

Good day



Cable attenuation at audio frequencies and I would include digital audio up to say 20MHz at length of say up to 50-100 feet, is not much of a problem to start with. The attenuation depends on BOTH cable and load. Even a 10 OHM cable resistance (very high) has tiny impact -.086dB attenuation, when the load is say 1KOhms.

So what will it take to have more attenuation? The conductor itself will have higher resistance as you raise temperature, by by how much? For copper it is 0.0039 per degree C, so if your wire is say 1 Ohm at room temperature, then it will be 1.097 Ohms at 50 degree C (122 degree F), so the attenuation for 10Ohm resistive cable (very high resistance) into 1K Ohm load will change from -.086dB at room temp at 25C to -.095dB at 50C.

So physics is great and talking about concepts is great, but for real world issue, engineering lets you QUANTIFY things.  
One can talk about loosing money, but you lose interest in the concept just as soon as you realize that the conversation is about losing .001 cent.

Regards
Dan Lavry
http://www.lavryengineering.com
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Bubblepuppy

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Re: a ?400 digital interconnect
« Reply #18 on: September 01, 2006, 02:04:08 AM »

Dan,
I would ask that you look into the eia/tia standards and the effect temperature has on cable, its more substantial than you seem to understand.
Engineering does not always represent reality, a humming bird should not be able to fly but it does.

You make the mistake of bringing the religon of engineering to the alter reality.

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Bubblepuppy

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Re: a ?400 digital interconnect
« Reply #19 on: September 01, 2006, 02:21:39 AM »

Here is another point of view on your conclusion

Attenuation causes

Okay, if the cable's varying length didn't cause the attenuation to change, what did?

To understand this, we have to understand what causes attenuation in the first place (for more on this, see pages 386-389 in Modern Cable Television Technology, by Ciciora, Farmer and Large). There are four fundamental reasons why cable has attenuation: signal leakage out of the cable because of less-than-ideal shielding; resistive losses in the cable's metallic conductors; signal absorption in the dielectric; and signal reflections caused by impedance mismatches.

Without getting too deep, the majority of attenuation comes from resistive losses in the cable's metallic conductors. What's of interest here is the conductors' resistivity, which is temperature-dependent. Resistivity is a "bulk property of material describing how well that material inhibits current flow. This is slightly different from resistance, which is not a physical property. If one considers current flowing through a unit cube of material (say, a solid metal cube that measures 1 meter on each side), resistivity is defined as the voltage measured across the unit cube length (V/m) divided by the current flowing through the unit cube's cross sectional area (I/m2). This results in units of Ohm m2/m or Ohm-m." [University of British Columbia Geophysical Inversion Facility]

In case you were wondering, the resistivity of copper is 1.673-8 Ohm-m, and aluminum is 2.650-8 Ohm-m, both at 68 degrees F. Each of these metals has a temperature coefficient of resistivity of about 0.22 percent/ degrees F. Conductor resistance varies as the square root of resistivity, so the resistance of the center conductor and shield (and the attenuation) changes about 0.11 percent / degrees F.

Yeah, but why?

Colliding electrons

Well, it's because the electrical resistance of a conductor such as copper or aluminum is dependent upon collisional processes within the metallic conductor. A closer look at conductivity shows it to be proportional to the mean free path between collisions (d). For temperatures above about 15K (that's kelvin...), d is limited by thermal vibration of atoms.

Huh?

Let's look at electrical conductivity (s = 1/r, where s is conductivity and r is resistivity--see, all this stuff is related!). Many metals make good conductors because they have lots of free charges--usually electrons--in them. When a voltage difference exists between two points in a metal, it creates an electric field that causes electrons to move--in other words, current!

The electrons bump into some of the metal's atoms, and this "frictional resistance" slows the electrons down. The greater the distance the electrons can travel without bumping into the metal's atoms, the lower the resistance and the greater the conductivity. The average distance an electron can travel without bumping into an atom is known as "mean free path."And how does temperature play a role in all of this? The higher the temperature, the more the metal's atoms jiggle around and get in the way of the electrons, causing the resistance to increase. At lower temperatures, the metal's atoms jiggle around less, so they don't get in the way of the electrons quite as much. The resistance decreases.

That's kind of a simplistic explanation of R = R0[1 + a(T - T0)]--(where R is the new resistance, R0 is the initial resistance, T0 is the initial temperature, T is the new temperature, and a is the temperature coefficient, but jiggling atoms are much more intuitive than mathematical formulas!
Ron Hranac is a consulting systems engineer for Cisco Systems, and senior technology editor for Communications Technology. You may reach him at rhranac@aol.com.



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Jon Hodgson

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Re: a ?400 digital interconnect
« Reply #20 on: September 01, 2006, 05:10:41 AM »

If you read what Dan wrote, you'll see that he's allowed for the 0.22% per degree F change in resistivity in the calculations he made, the ones where he concluded a .009 dB change in attenuation was insignificant.

I tend to agree.

That book you refer to is about cables for television, I don't have it but I would say that the environment it is concerned about dealing with
1) Uses higher frequencies than anything an audio cable has to deal with, even a digital audio one
2) Traverses over MUCH greater distances than you get in a studio, or even a live show
3) Is far more cost constrained, you go laying thousands of miles of cable and putting in hundreds of thousands of receivers and transmitters, cost per unit becomes very important, so you tend to design to the minimum that will work reliably.

But as it happens, Dan already considered the maths involved in his evaluation. He just showed that the results approximate to zero when applied to the environment he is concerned with
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danlavry

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Re: a ?400 digital interconnect
« Reply #21 on: September 01, 2006, 02:49:20 PM »

Bubblepuppy wrote on Fri, 01 September 2006 07:21

Here is another point of view on your conclusion

Attenuation causes

Okay, if the cable's varying length didn't cause the attenuation to change, what did?

To understand this, we have to understand what causes attenuation in the first place (for more on this, see pages 386-389 in Modern Cable Television Technology, by Ciciora, Farmer and Large). There are four fundamental reasons why cable has attenuation: signal leakage out of the cable because of less-than-ideal shielding; resistive losses in the cable's metallic conductors; signal absorption in the dielectric; and signal reflections caused by impedance mismatches.

Without getting too deep, the majority of attenuation comes from resistive losses in the cable's metallic conductors. What's of interest here is the conductors' resistivity, which is temperature-dependent. Resistivity is a "bulk property of material describing how well that material inhibits current flow. This is slightly different from resistance, which is not a physical property. If one considers current flowing through a unit cube of material (say, a solid metal cube that measures 1 meter on each side), resistivity is defined as the voltage measured across the unit cube length (V/m) divided by the current flowing through the unit cube's cross sectional area (I/m2). This results in units of Ohm m2/m or Ohm-m." [University of British Columbia Geophysical Inversion Facility]

In case you were wondering, the resistivity of copper is 1.673-8 Ohm-m, and aluminum is 2.650-8 Ohm-m, both at 68 degrees F. Each of these metals has a temperature coefficient of resistivity of about 0.22 percent/ degrees F. Conductor resistance varies as the square root of resistivity, so the resistance of the center conductor and shield (and the attenuation) changes about 0.11 percent / degrees F.

Yeah, but why?

Colliding electrons

Well, it's because the electrical resistance of a conductor such as copper or aluminum is dependent upon collisional processes within the metallic conductor. A closer look at conductivity shows it to be proportional to the mean free path between collisions (d). For temperatures above about 15K (that's kelvin...), d is limited by thermal vibration of atoms.

Huh?

Let's look at electrical conductivity (s = 1/r, where s is conductivity and r is resistivity--see, all this stuff is related!). Many metals make good conductors because they have lots of free charges--usually electrons--in them. When a voltage difference exists between two points in a metal, it creates an electric field that causes electrons to move--in other words, current!

The electrons bump into some of the metal's atoms, and this "frictional resistance" slows the electrons down. The greater the distance the electrons can travel without bumping into the metal's atoms, the lower the resistance and the greater the conductivity. The average distance an electron can travel without bumping into an atom is known as "mean free path."And how does temperature play a role in all of this? The higher the temperature, the more the metal's atoms jiggle around and get in the way of the electrons, causing the resistance to increase. At lower temperatures, the metal's atoms jiggle around less, so they don't get in the way of the electrons quite as much. The resistance decreases.

That's kind of a simplistic explanation of R = R0[1 + a(T - T0)]--(where R is the new resistance, R0 is the initial resistance, T0 is the initial temperature, T is the new temperature, and a is the temperature coefficient, but jiggling atoms are much more intuitive than mathematical formulas!
Ron Hranac is a consulting systems engineer for Cisco Systems, and senior technology editor for Communications Technology. You may reach him at rhranac@aol.com.





First, again: the copper resistivity of a cable by itself is not enough to tell you about attenuation! You need to know the LOAD! As I mentioned elsewhere on this forum, a 1 Ohm resistance is a cause to a lot of attenuation when you are dealing with say an 8 Ohm speaker. You can not discount math. The attenuation is A=RL/(Rload+Rcable) in this case A=8/9 or in dB it is -1dB. So at 8Ohms it is a lot of loss. But raise the load to say 600 Ohms then A=-.014dB.

You can not talk about the sound of one hand clapping.  
Similarly, you can not talk attenuation looking at one hand (the cable) and not the other (the load).

You mentioned 4 reasons for loss, with the conductor resistance being the main one, and you "elaborated some". But besides the fact that you did not mentioned load, you did not touch on the fact that the signal frequency content is also a major KEY.
I keep qualifying my statements over and over, saying "for audio signals" and for "digital audio up to say 25MHz and 100 feet"...

The conductor resistance is important at very high frequencies, when only the thin outer diameter carries current (skin effect). I wrote a paper on skin effect (see it at my forum at www.lavryengineering.com). But we are not talking about GHz signals. We are talking about up to 25MHz. Also, skin effect increases with cable length and here we are not talking about miles of cable runs...

I am pretty sure that your referenced person from cisco would not have any issues with what I am saying. He will have issues with what you are saying! You are talking out of context! We are talking and dealing with very low frequencies, when referenced to what cisco is doing. On top of it, one should examine the load as well as the cable length.

A thirsty person can be highly impacted by one cup of water. But the same cup will make insignificant difference in the Atlantic ocean. You seem to reach general conclusions about the importance of that cup of water, but in fact it does matter a lot in one case, and it does not in the other.

Similarly, the impact of skin effect in the applications we are talking about is NEGLIGIBLE. The temperature effects are also NEGLIGIBLE. Thank you for "friction" explanation (a very simplistic one) of how the copper resistivity goes up with temperature, but that does NOT alter the fact that the coefficient describing the rise of resistance over temperature is 0.0039 per degree C, nor does it alter that at low frequencies, attenuation is a voltage divider action between series resistance and load.

The audio industry is full of "mention" of things that are there, but are mentioned out of context. The fact is, skin effect does occur even when at 1Hz frequency and 1 inch length. A single drop of water will increase the volume of the ocean. But the effect of 1 billionth of a billionth of a dB can be ignored in the real world. What is missing in such arguments is a real world perspective, and engineering IS of value here. Engineering is not just a bunch of formulas! It is hands on experience and measurement based.

Also, many of those that are less familiar with math, engineering and science, often make a judgment error, by assuming that "things are proportional". For example, if I tell someone that a cable of a certain length causes say 1dB loss at 1GHz, it is WRONG to assume that you will have 0.5dB loss ate 0.5GHz (500Mhz), and .1dB at 100MHz. Not only does the math for dB is not linear. Not only does the math for attenuation is not linear. The physics itself is highly non linear. Again, look at the skin effect paper on my site.

You said:
"That's kind of a simplistic explanation of R = R0[1 + a(T - T0)]".

I say: It is very easy to dismiss a statement. It is simplistic in some cases, and rather accurate in other cases. It is rather accurate at the frequencies and cable length for audio. Just calling something simplistic is of no value. You have to point out why, how and or at least QUANTIFY what you say, which you did not.

I can go on, but it is getting too long.

Regards
Dan Lavry
http://www.lavryengineering.com
   
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Bubblepuppy

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Re: a £400 digital interconnect
« Reply #22 on: September 02, 2006, 03:22:41 PM »

Category 6
100 meters maximum length
100 ohms
4 pair UTP
ANSI/TIA/EIA-568-b.2-1 -June 2002 ISO/IEC 11801-2002

These are the building blocks of future digital audio.
In this world of real Bandwidth (200Mhz PSACR)
And now with the acceptance of 6A (500Mhz PSACR)10 gigabit over 4 pair utp copper IMHO will be the language your hardware will be required to speak.

My initial point was engineering standards are not written for overkill, because that gives the impression it considers all possible hazards.
Most standards ( expecialially in the audio world) limit the scope of applications to attain financial feasibility.
And this is where most standards eventually fall by the wayside.
Toslink(Crap)
AdatLightPipe(Crap)
And maybe even MADI


Pro audio will be forced to look beyond its current view and move toward broader applications.
You will be required in the very near future to talk to Cisco/HP/Extreme-Networks etc..

MADI Basics (excerpt from the HDSP MADI manual)

MADI, the serial Multichannel Audio Digital Interface, has been defined already in 1989 as an extension of the existing AES3 standard following several manufacturer's wish. The format also known as AES/EBU, a balanced bi-phase signal, is limited to two channels. Simply put, MADI contains 28 of those AES/EBU signals in serial, i. e. after one another, and the sample rate can still even vary by +/-12.5%. The limit which cannot be exceeded is a data rate of 100Mbit/s. Because an exact sampling frequency is used in most cases, the 64 channel mode was introduced officially in 2001. It allows for a maximum sample rate of 48 kHz + ca. 1%, corresponding to 32 channels at 96 kHz, without exceeding the maximum data rate of 100 Mbit/s. The effective data rate of the port is 125 Mbit/s due to additional coding. Older devices understand and generate only the 56 channel format. Newer devices often work in the 64 channel format, but offer still no more than 56 audio channels. The rest is being eaten up by control commands for mixer settings etc.. The ADI-648 and the HDSP MADI show that this can be done in a much better way, with an invisible transmission of 16 MIDI channels and the MADI signal still being 100% compatible. For the transmission of the MADI signal, proved methods known from network technology were applied. Most people know unbalanced (coaxial) cables with 75 Ohms BNC plugs, they are not expensive and easy to get.

The optical interface is much more interesting due to its complete galvanic separation, but for many users it is a mystery, because very few have ever dealt with huge cabinets full of professional network technology. Therefore here are some explanations regarding 'MADI optical'. The cables used are standard in computer network technology. They are thus not at all expensive, but unfortunately not available in every computer store. The cables have an internal fibre of only 50 or 62.5
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Jon Hodgson

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Re: a £400 digital interconnect
« Reply #23 on: September 02, 2006, 05:21:02 PM »

Bubblepuppy wrote on Sat, 02 September 2006 20:22

Point 1
without exceeding the maximum data rate of 100 Mbit/s. The effective data rate of the port is 125 Mbit/s due to additional coding.
100Mbits is a insult to the word ProAudio ( 1000baseT has been available since January 2000).



MADI is a lot older than 6 years.

In addition 100MBits is 64 channels at 48KHz and 32 at 96kHz, all through a single coax, not an insult to the term pro audio at all. There aren't that many places where you need to transfer a large number of channels together anyway, recorder to mixer, mixer to dac. Most outboard is stereo.

You're looking at the spec of MADI cables and complaining that they're not adequate for passing 1GBits??? The question that needs to be asked is, does the spec for MADI cables allow for the reliable bit true transmission of MADI spec signals? The answer is yes.

If we want to transmit 1000 Base T signals, we'll use 1000 Base T spec cables.
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Bubblepuppy

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Re: a £400 digital interconnect
« Reply #24 on: September 02, 2006, 06:54:59 PM »

In addition 100MBits is 64 channels at 48KHz and 32 at 96kHz, all through a single coax, not an insult to the term pro audio at all. There aren't that many places where you need to transfer a large number of channels together anyway, recorder to mixer, mixer to dac. Most outboard is stereo.

Excuse me, Pro-tools is one example, we have a latency problem in digital audio.
You also ignore my point on physical issues with Coaxial cable and high bandwidth.

And I must disagree but 100Mbits is pathetic.
How about real time control and Hi def video supported on the same format.
Or the latency issues when running 96 digital inputs @ 192Khz through one console as well as automation and native HD video.
And you completly ignored the (Plastic) Fiber point and connector issue.

And most outboard is stereo, why not have outboard equipt that works in native 7.1 surround with selectable sample rates.

Once again the response seems "myopic"

I would hope forward thinking like supporting HI-DEF video and hi-def selectable audio 44.1/48/96/88.2/192 24bits/32/bits/64bits on one datastream is where we need to look rather than trying to defend the 100Mbit (buggy-whip) standard.

IMHO


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Jon Hodgson

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Re: a £400 digital interconnect
« Reply #25 on: September 02, 2006, 07:29:17 PM »

Bubblepuppy wrote on Sat, 02 September 2006 23:54


Excuse me, Pro-tools is one example, we have a latency problem in digital audio.


And a higher datarate transmission will help this latency how? It won't, the latency remains the same, you just have more channels.
Bubblepuppy wrote on Sat, 02 September 2006 23:54

You also ignore my point on physical issues with Coaxial cable and high bandwidth.


No I didn't, I said that the question is whether or not the cable specification is adequate to ensure correct transmission of the data.
Quote:

And I must disagree but 100Mbits is pathetic.
How about real time control and Hi def video supported on the same format.

That's a DIFFERENT INTERFACE so what is the point of looking at cable specs for the MADI Interface in that context??

Quote:

Or the latency issues when running 96 digital inputs @ 192Khz through one console as well as automation and native HD video.

Again, latency is not going to be affected, whether you use multiple MADI interfaces in parallel or one super high speed interface.

Quote:

And you completly ignored the (Plastic) Fiber point and connector issue.

Again, DOES IT DO THE JOB BEING ASKED OF IT??

Quote:

And most outboard is stereo, why not have outboard equipt that works in native 7.1 surround with selectable sample rates.

Once again the response seems "myopic"

I would hope forward thinking like supporting HI-DEF video and hi-def selectable audio 44.1/48/96/88.2/192 24bits/32/bits/64bits on one datastream is where we need to look rather than trying to defend the 100Mbit (buggy-whip) standard.


You are confusing two seperate issues in your argument, you try to use what you consider to be inadequacies in the interface standard to say that the connections specified are inadequate for that interface.

As for bringing in new interface standards, well it is happening, but its a very slow process, that has more to do with the nature of the business than any lack of vision by the engineers involved. Gear in the music industry tends to have lifespans much greater than in the computer industry, when the whole industry is running quite happily using AES and MADI interfaces, there has to be a compelling reason for them to introduce a new standard into their setups.




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Bubblepuppy

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Re: a £400 digital interconnect
« Reply #26 on: September 03, 2006, 01:22:47 AM »

And a higher datarate transmission will help this latency how? It won't, the latency remains the same, you just have more channels.
Baudrate/ datarate /clockspeed /bussspeeds effect latency, nothing can remove it you can minimize its impact on realtime performance.
Increase the datarate/clockspeed through-put which gets everyone in to the buffer quicker, faster 32/64 bit bus speeds increase clock cycle efficiency and delivery.
12-level coded PAM signalling (3.2 information bits/Symbol) Tomlinson-Harashima precoder at TX.
Full duplex echo-cancelled transmission, 800 MBaud, - 500Mhz used bandwidth.
And wallah! 10gig over 4pair copper 328' max length.
This will definitely improve latency when processors are not waiting for more packets to arrive to be reassembled and provides plenty of data band width to deal with bit errors which slow down the overall system performance.

Since bit errors exist in all digital devices, processors need time and extra data processing power to deal with this problem before delayed delivery of information increases delays into the 10ms range.
Very high (data) bandwidth delivery is whats needed to deal with 24/48 channels of 16/24/32/64bit packets of real time audio.
As for plastic glass its not doing the job, plastic fiber was a response during the dot.com craze where fiber lead times were 18 to 24 months.
If you had to throw something into the ground because you only had a 6 month window, avoid the law suit and install it.
Its junk, was junk and is still junk period.
I would recommend you do some research on fiber before you assume it is doing what you are being told it will do!
I deal with networks and fiber applications every day,
plastic was used mainly in slow speed systems.
LED Over fill launch application for MM fiber.
Vcsel lasers now replace that to improve cycle time, lasers can fire much faster than LEDs, hence faster delivery and increased data OC192 ( 10 GIG )
Smile


 
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Jon Hodgson

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Re: a £400 digital interconnect
« Reply #27 on: September 03, 2006, 04:46:46 AM »

Bubblepuppy wrote on Sun, 03 September 2006 06:22

And a higher datarate transmission will help this latency how? It won't, the latency remains the same, you just have more channels.
Baudrate/ datarate /clockspeed /bussspeeds effect latency, nothing can remove it you can minimize its impact on realtime performance.
Increase the datarate/clockspeed through-put which gets everyone in to the buffer quicker, faster 32/64 bit bus speeds increase clock cycle efficiency and delivery.
12-level coded PAM signalling (3.2 information bits/Symbol) Tomlinson-Harashima precoder at TX.
Full duplex echo-cancelled transmission, 800 MBaud, - 500Mhz used bandwidth.
And wallah! 10gig over 4pair copper 328' max length.
This will definitely improve latency when processors are not waiting for more packets to arrive to be reassembled and provides plenty of data band width to deal with bit errors which slow down the overall system performance.

Since bit errors exist in all digital devices, processors need time and extra data processing power to deal with this problem before delayed delivery of information increases delays into the 10ms range.
Very high (data) bandwidth delivery is whats needed to deal with 24/48 channels of 16/24/32/64bit packets of real time audio.
As for plastic glass its not doing the job, plastic fiber was a response during the dot.com craze where fiber lead times were 18 to 24 months.
If you had to throw something into the ground because you only had a 6 month window, avoid the law suit and install it.
Its junk, was junk and is still junk period.
I would recommend you do some research on fiber before you assume it is doing what you are being told it will do!
I deal with networks and fiber applications every day,
plastic was used mainly in slow speed systems.
LED Over fill launch application for MM fiber.
Vcsel lasers now replace that to improve cycle time, lasers can fire much faster than LEDs, hence faster delivery and increased data OC192 ( 10 GIG )
Smile


 


Firstly as far as latency is concerned, we're talking about a constant stream of n channels ryunning at x kHz. The receiver cannot do anything with the audio until it has received all n xhannels, so basically it needs to get one frame of audio before it can pas it on. Increasoing the bit rate of the channel doesn't really help, we'll still have to wait one sample period before the next frame arrives. But since we're talking about a period of 22 or 11 microseconds (44 or 88kHz( this is not an audible latency anyway. If there is an audible latency problem, it is not with the audio channel.

As for bit errors existing in all digital devices, you're showing your lack of engineering knowledge, it is not true. It is true that many communications system are designed to tolerate a number of errors in the transmision, and then the chanels are specified such that errors should be kept below what can be dealt with (but will usually be above zero), but this is not the case with AES and MADI, they have been designed such that what you put in is what you get out, with no further error correction, in fact there is no provision for error correction in them, only detection.

As for plastic glass, once again you start ranting about its use in a cimpletely different context. It doesn't matter what they put in the ground because it was cheap, optical connections for madi are not run over long distances.

Plastic was used mostly in low speed systems? Not a problems really since in modern comms terms MADI is, as you keep pointing out, a slow system, and on top of that the distances involved are a fraction of what you experience in the comms industry,

You may deal with networks and fibre applications every day, but it seems to me you are not an engineer, and you don't actually understand all the actual practical implications of numbers and terms you quote so impressively when applied to a specific situation.
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Yannick Willox

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Re: a £400 digital interconnect
« Reply #28 on: September 03, 2006, 07:02:02 AM »

As an end user, I did not invest in MADI (although I really need a multichannel digital carrier that is robust enough for live use), just because of these reservations.

The cables that are sold are not OK. I was on the point of buying two MADI/AES converters, but was not able to source non-plastic cable from audio dealers. Contacting the constructor did not help. I had to contact a network company (eg Black Box) to have the glass cables constructed and test myself (!). This was for distances above 50m.

I would say either it is under engineered, or the real world performance is neglected.

Of course 50m with plastic would work, but then you start using 32 ch at 96K, what happens ? On a bad day - in a live situation ? I do not want to be bothered by this, and I have the impression manufacturers do not like to be bothered by this either. They think safe/studio/fixed/short installations.

Also, does MADI not carry the clock ? If I understand correctly, the interface gets near its theoretical maximum when using all channels - so what happens to the CLOCK in this case ?
Did anybody do some tests on a MADI interface with all channels sending/receiving data ?

Yes you can still use wordclock, but doesn't Bubblepuppy have a point, if it had been overengineered instead of just enough bandwith engineered, there would be no potential problem.
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Bubblepuppy

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Re: a £400 digital interconnect
« Reply #29 on: September 03, 2006, 07:22:55 AM »

As for bit errors existing in all digital devices, you're showing your lack of engineering knowledge, it is not true. It is true that many communications system are designed to tolerate a number of errors in the transmission, and then the channels are specified such that errors should be kept below what can be dealt with (but will usually be above zero), but this is not the case with AES and MADI, they have been designed such that what you put in is what you get out, with no further error correction, in fact there is no provision for error correction in them, only detection.

Every digital device has errors, Period.


Read this,
The use of Reed-solomon code.

"In analog audio, there is no chance for error correction. If you record the signal damaged, it is damaged until the end. But with digital audio, the nature of binary, lends itself to fix the damage.

When audio data is transmitted or stored, it is coded and accompanied by redundancy. This enables the reproduced data to be checked for errors. Discovered errors can then be corrected or be concealed by creating new data.

An error correction system comprises three operations:

Error detection uses redundancy to permit data to be checked for validity

Error correction uses redundancy to replace erroneous data with newly calculated valid data.

In the event of large errors or insufficient data for correction, error concealment techniques substitute approximately correct data for invalid data.
Two Kinds of Errors -

Random Bit
Errors, occurring singly, that have no relation to each other and are easily corrected. Where individual bits are corrupted.
Burst Errors
A large sustained error where a sequence of bits are corrupted (e.g. CD scratch). Results in data and redundant data loss and is difficult to correct."

Like I said all digital devices make and send errors, period.

"The first and most effective error correction is recorded onto the tape in the form of Reed-Solomon error-correction codes. These codes take up more than 25 percent of the data on a DAT tape or CD, and they allow most errors (this means transmitted) to be completely corrected, yielding data that is byte-for-byte perfect."

your statement
"AES and MADI, they have been designed such that what you put in is what you get out, with no further error correction, in fact there is no provision for error correction in them, only detection.

Is simply not true, what you put in uses redundancy and error-correction to rebuild what was originally sent in spite of the errors. They are always there.

No I am not an EE, just deal with them on a daily basis.
Cheers!

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Jon Hodgson

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Re: a £400 digital interconnect
« Reply #30 on: September 03, 2006, 07:49:37 AM »

Bubblepuppy wrote on Sun, 03 September 2006 12:22


"AES and MADI, they have been designed such that what you put in is what you get out, with no further error correction, in fact there is no provision for error correction in them, only detection.

Is simply not true, what you put in uses redundancy and error-correction to rebuild what was originally sent in spite of the errors. They are always there.

No I am not an EE, just deal with them on a daily basis.
Cheers!




Firstly I am an EE, and a Software Engineer also, and I've known about Reed Solomon for nearly 20 years, before I even went to university for my degree, incidentally I've known about the reason that resistance of a conductor increases with temperature for a similar amount of time, just because it's new to you doesn't mean that engineers haven't known about it and designing with it for a long time.

Secondly, do you have the MADI spec to hand? The AES spec?

I do, and I can understand what they say.

Neither of those systems transmits redundant bits for error correction at the receiver.

Actually many transmission channels don't, the connections on a chip, connections between chips, rs232, midi, none of them has any kind of error correction.


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Bubblepuppy

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Re: a £400 digital interconnect
« Reply #31 on: September 03, 2006, 08:57:55 AM »

Firstly I am an EE, and a Software Engineer

I wont hold that against you I promise.

just because it's new to you doesn't mean that engineers haven't known about it and designing with it for a long time.

Its not new to me, its just enginners think the lab is the real world.

Finally, your position is MADI & AES digital communications never have errors?

I give up, if its written in the spec then it must be true....
I think I will sell my new MAC dual core intel go find a 386 and live with the blazing speed of 100Mbits that never has any errors and more than eneough speed to meet all my audio needs.

PLEASE.

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Jon Hodgson

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Re: a £400 digital interconnect
« Reply #32 on: September 03, 2006, 09:15:30 AM »

Bubblepuppy wrote on Sun, 03 September 2006 13:57

Firstly I am an EE, and a Software Engineer

I wont hold that against you I promise.

just because it's new to you doesn't mean that engineers haven't known about it and designing with it for a long time.

Its not new to me, its just enginners think the lab is the real world.

Finally, your position is MADI & AES digital communications never have errors?

I give up, if its written in the spec then it must be true....
I think I will sell my new MAC dual core intel go find a 386 and live with the blazing speed of 100Mbits that never has any errors and more than eneough speed to meet all my audio needs.

PLEASE.


No I didn't say they never have errors

I said that if everything is in spec, including the environnent, then there are no errors. I am also saying that the format does not have any contingency for error correction, only detection. If it gets corrupted, it's lost, end of story.

You claimed that all communication channels use error correction systems involving the transmission of redundant data, you were wrong, PERIOD.

And what does the speed of the processor have to do with the speed of the link? Nothing. Just because I maintain that MADI is perfectly adequate to do what it is supposed to do, transmit 32 channels of 96kHz digital audio over distances up to 50m, does not mean that I don't think that there are situations where more channels, video, or some other feature is desirable. In that case I will look at an interface that handles that, and the cabling required.

You try to argue your position by quoting numbers and specifications you don't acually understand, then when you're called on them you accuse engineers of being the ones tied to specs?


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Bubblepuppy

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Re: a £400 digital interconnect
« Reply #33 on: September 03, 2006, 09:42:29 AM »

Isnt detection a contengcy for dealing with errors?

Smile
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Bubblepuppy

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Re: a £400 digital interconnect
« Reply #34 on: September 03, 2006, 09:47:37 AM »

Have you ever tried to send 100mbits with a 286?
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Jon Hodgson

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Re: a £400 digital interconnect
« Reply #35 on: September 03, 2006, 09:54:17 AM »

Bubblepuppy wrote on Sun, 03 September 2006 14:42

Isnt detection a contengcy for dealing with errors?

Smile


Contingent yes, sufficient NO

Try learning about Reed Solomon and similar codes before quoting them at people
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Bubblepuppy

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Re: a £400 digital interconnect
« Reply #36 on: September 03, 2006, 10:00:28 AM »

"I am also saying that the format does not have any contingency for error correction, only detection"

"Contingent yes, sufficient NO"

I think we need error correction here.
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Jon Hodgson

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Re: a £400 digital interconnect
« Reply #37 on: September 03, 2006, 10:17:47 AM »

Bubblepuppy wrote on Sun, 03 September 2006 15:00

"I am also saying that the format does not have any contingency for error correction, only detection"

"Contingent yes, sufficient NO"

I think we need error correction here.



You're playing semantics despite having been wrong.

AES allows for detection of some errors, it does not allow for correction of those errors. Is that clear enough for you?
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Bubblepuppy

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Re: a £400 digital interconnect
« Reply #38 on: September 03, 2006, 03:48:56 PM »

You claimed that all communication channels use error correction systems involving the transmission of redundant data, you were wrong, PERIOD.

Question,
Then explain to me
Cycle Redundancy check sum (Byte 23)
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Jon Hodgson

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Re: a £400 digital interconnect
« Reply #39 on: September 03, 2006, 04:06:45 PM »

Bubblepuppy wrote on Sun, 03 September 2006 20:48

You claimed that all communication channels use error correction systems involving the transmission of redundant data, you were wrong, PERIOD.

Question,
Then explain to me
Cycle Redundancy check sum (Byte 23)



Quoting from John Watkinson's "The Art of Digital Audio"

"The final byte in the message is a CRCC which converts the entire channel-status block into a codeword. The channel-status message takes 4ms at 48kHz and in this time the router could have switched to another signal source. This would damage the transmission and also result in a CRCC failure, so the corrupt block is not used. Error correction is not necessary, as the channel-status data are either stationary, i.e. they stay the same, or change at a predictable rate, e.g. timecode. Stationary data will only change at the receiver if a good CRCC is obtained".

Note 2 things
1) Error DETECTION, not correction
2) The CRCC applies only to the status block, not the audio data.

There is one other error detection mechanism in the transmission, that is a parity bit on each word transmitted. This is only capable of detecting a single bit error, which indicates that errors are only expected under very extreme circumstances.
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Jon Hodgson

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Re: a £400 digital interconnect
« Reply #40 on: September 03, 2006, 04:58:09 PM »

Yannick Willox wrote on Sun, 03 September 2006 12:02

As an end user, I did not invest in MADI (although I really need a multichannel digital carrier that is robust enough for live use), just because of these reservations.

The cables that are sold are not OK. I was on the point of buying two MADI/AES converters, but was not able to source non-plastic cable from audio dealers. Contacting the constructor did not help. I had to contact a network company (eg Black Box) to have the glass cables constructed and test myself (!). This was for distances above 50m.

I would say either it is under engineered, or the real world performance is neglected.

Of course 50m with plastic would work, but then you start using 32 ch at 96K, what happens ? On a bad day - in a live situation ? I do not want to be bothered by this, and I have the impression manufacturers do not like to be bothered by this either. They think safe/studio/fixed/short installations.

Also, does MADI not carry the clock ? If I understand correctly, the interface gets near its theoretical maximum when using all channels - so what happens to the CLOCK in this case ?
Did anybody do some tests on a MADI interface with all channels sending/receiving data ?

Yes you can still use wordclock, but doesn't Bubblepuppy have a point, if it had been overengineered instead of just enough bandwith engineered, there would be no potential problem.


In today's world where gigabit ethernet comes built in to a Max at no extra cost it is very easy to look at AES/EBU and MADI and say they were underengineered. You have to look at the situation when they were devised.


AES was devised over 20 years ago, to replace a number of similar but incompatible standards, it also had to work along cables that people had already laid in their studios, and be affordable.

MADI is almost as old, when it was brought in even 10 MBit networks were rare, a 100MBit connection ove one cable really was cutting edge. Sure they could have devised something that could transmit 1 gig, do 300 channels of audio or include video etc, but it would have been way too expensive for anyone to implement, and been stillborn.

The fact is that 20 years after they were devised both these stamdards still do such a good job, in so many situations (want to transfer 32 channels of 96kHz audio from your recorder to your mixer along one cable? No problem, MADI does that fine. Want to connect your converters to your recorder? it can do that.), to me that's a pretty well designed interface.

Could we do a better job if we were starting today? Sure, but these guys were working 20 years ago.
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Andy Peters

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Re: a £400 digital interconnect
« Reply #41 on: September 04, 2006, 08:35:21 PM »

Bubblepuppy wrote on Sun, 03 September 2006 06:47

Have you ever tried to send 100mbits with a 286?


So you're blaming lack of processing horsepower as the reason why you can't keep a 100 mbps pipe full?

If you compared apples with another fruit, your arguments would hold more water.  As it is, you compare apples to Buicks.

-a
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Andy Peters

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Re: a £400 digital interconnect
« Reply #42 on: September 04, 2006, 08:54:44 PM »

Bubblepuppy wrote on Sun, 03 September 2006 04:22

Every digital device has errors, Period.


Actually, that's not true.  Error-free digital electronics is in use every day, all the time.

Quote:

The use of Reed-solomon code.

(snip)

When audio data is (sic) transmitted or stored, it is coded and accompanied by redundancy.


See, now you really miss the important point here: "when audio are transmitted or stored" is too simplistic.  CDs, as an example, use RS coding because it is expected that the discs can suffer physical damage simply because they are mechanical items and are handled by users who won't take care of them.  Hard disk data are similarly encoded because as a mechanical medium it is susceptible to physical wear and tear (although no amount of RS coding will help when the bearings die).

If you transmit data over a medium that's subject to change (wireless transmission, transmission over long distances, transmission over a medium that a user can disconnect/change) then error detection and correction makes sense.

On the other hand, if you're interested in getting data from processor A to memory B over a well-defined electrical backplane where operation is in accordance with all relevent specs and design parameters, then you can dispense with the overhead of ECC.  For example, it's always been possible to buy a computer that uses ECC memory.  In practice, most users don't bother, and it's not a problem.  Why?  Because as long as you use the memory specified by your motherboard manufacturer and you don't do something stupid like overclock, then you're operating correctly and you won't have problems.

People who DO have memory problems either use the wrong memory, or they've installed it incorrectly.  In some rare instances, some memory locations may go bad because of a static zap.  When this happens, the whole system tends to lock up; ECC doesn't do much good when the results of a memory read are all 0xFF for all bytes and parity bits.

Quote:

No I am not an EE, just deal with them on a daily basis.


You seem to hold them (errr, us, as both Jon and I, and Dan, and others, are EEs) in contempt.

What's your background?

-a
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danlavry

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Re: a £400 digital interconnect
« Reply #43 on: September 05, 2006, 01:38:38 PM »

Bubblepuppy wrote on Sun, 03 September 2006 13:57

Firstly I am an EE, and a Software Engineer

I wont hold that against you I promise.

just because it's new to you doesn't mean that engineers haven't known about it and designing with it for a long time.

Its not new to me, its just enginners think the lab is the real world.

Finally, your position is MADI & AES digital communications never have errors?

I give up, if its written in the spec then it must be true....
I think I will sell my new MAC dual core intel go find a 386 and live with the blazing speed of 100Mbits that never has any errors and more than eneough speed to meet all my audio needs.

PLEASE.




I am back from a long weekend, and I see that the subject has changed completely. Instead of dealing with the comment about the effect or lack of effect of temperature on attenuation, instead of acknowledgment that the load DOES matter, instead of agreement that for audio frequency applications (under say 50KHz) the load resistance is higher then 600 Ohms (often 10KOhms) and that for 25MHz signals, which is most of digital audio interconnect, you chose to make a sharp turn, and talk about future formats that raise the frequencies to 1GHz.

Well, most readers that are not technical, would need to have a CLEAR DISTINCTION that will enable them to know that as long as they are dealing with analog audio or AES or SPDIF the temperature DOES NOT MATTER to cable attenuation. I am doing my part - I keep stating the parameters (less then 100 feet and under 25MHz) and that is a lot of margin!

Instead of conceding in a clear way that what I said is correct under the conditions (or that as a non EE you are in no position to know it), you keep arguing a different point, so in some indirect sense, you are "dragging" the argument to a different area where you may be correct. In GHz applications the skin effect is important, and so are other factors.

There have been some systems designed to distribute a lot of audio over high speed links, from Cat5 to optical... Some have been better then others. The engineering challenges of high speed communications will not be solved by the audio industry, and any audio engineer that want to send audio or anything else over the Internet will most likely use cables that meet the standards of Internet communications.

But coming here to an audio forum with a general claim that temperature rise will effect cable attenuation, INITIALLY WITHOUT A STATEMENT ABOUT THE VERY HIGH FREQUENCIES is way off. It is only AFTER I wrote my post that the issue does not exists at lower frequencies, that you started talking about GHz frequencies.

Again, in the cases that are of Daly interest to the audio people, such as cables for analog line levels and frequencies, or mic cables, or AES cables or SPDIF cables, the cable;e temperature is NOT a factor effecting attenuation!!!

When an audio person will need to send GHZ of data accross a network, they will resort to cables that are appropriate for a network. You can argue about skin effect, temperature and more for such applications. But a general statement on an audio forum that a cable temperature will cause attenuation creates the false impression that audio people should worry or consider the temperature of their cables. There are some important cable characteristics that are important factors for audio, for the sound itself. Temperature is NOT one of them.

Dan Lavry
http://www.lavryengineering.com

   

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Jon Hodgson

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Re: a £400 digital interconnect
« Reply #44 on: September 05, 2006, 01:57:59 PM »

Yannick Willox wrote on Sun, 03 September 2006 12:02

As an end user, I did not invest in MADI (although I really need a multichannel digital carrier that is robust enough for live use), just because of these reservations.

The cables that are sold are not OK. I was on the point of buying two MADI/AES converters, but was not able to source non-plastic cable from audio dealers. Contacting the constructor did not help. I had to contact a network company (eg Black Box) to have the glass cables constructed and test myself (!). This was for distances above 50m.

I would say either it is under engineered, or the real world performance is neglected.
.

What is your reasoning for this? Do you have any figures that show that when used with cables of the required spec, be they plastic or glass, that it doesn't do what it's supposed to?

Quote:

Of course 50m with plastic would work, but then you start using 32 ch at 96K, what happens ? On a bad day - in a live situation ?

Whether you are transmitting one channel at 32kHz or 32 at 96kHz the situation is the same. MADI is a fixed data rate transmission, what changes is how much of that data is filled in the transmitter and used at the receiver.

Quote:

I do not want to be bothered by this, and I have the impression manufacturers do not like to be bothered by this either. They think safe/studio/fixed/short installations.


Actually they think of a balance between different performance objectives and cost, with presently available technology (MADI was specced around 89). For the same cost they could possibly have guaranteed transmission over longer distances... but with fewer channels, or they could possibly have given it more channels, but with shorter distances. They might possibly have been able to improve either without reducing the other, but then the cost would have gone up, and bear in mind that when MADI was introduced it was already really expensive, it took many years before it became viable as a project studio format.

Quote:

Also, does MADI not carry the clock ? If I understand correctly, the interface gets near its theoretical maximum when using all channels - so what happens to the CLOCK in this case ?

MADI doesn't carry the clock, you need a seperate wordclock or AES connection for that.

Quote:

Did anybody do some tests on a MADI interface with all channels sending/receiving data ?


Yes, everyone who's ever used it. As I said MADI always transmits the same amount of data at the same rate, what changes is the content of that data.

Quote:

Yes you can still use wordclock, but doesn't Bubblepuppy have a point, if it had been overengineered instead of just enough bandwith engineered, there would be no potential problem.


If it was overengineered it would never have been viable at the time it was introduced, they needed a solution that could be implemented then, not one that they would have to wait years before it became financially and technically viable.
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Yannick Willox

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Re: a £400 digital interconnect
« Reply #45 on: September 06, 2006, 04:59:34 AM »

Thanks, that clears up a lot. No clock, constant amount of data.

I don't have numbers on cables, but was told and found info in several places that using plastic (standard ?) cable in live conditions over 50m could become problematic.
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Yannick Willox
Acoustic Recording Service
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