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Author Topic: a £400 digital interconnect  (Read 22992 times)

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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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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Yannick Willox
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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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