Splitters and Digital Audio Snakes

[James_uclan]

Good afternoon everyone. I'm having a slight dilemma at the moment in that I've been researching digital audio snakes for quite some time and am boggled about how they work. I'm currently doing a dissertation on Outside Broadcast and the last part involves writing about linking audio via splitters and audio snakes to the OB van, the FOH desk and onstage PA. I'm currently in a bit of a pickly in that I have never had the oppurtunity to work with any of this equipment before with my experience being in a television studio, and without having had hands on experience I've found reading about the equipment to be quite confusing, and mind boggling, however I'm sure using the equipment cannot be quite as tricky! I was wondering whether anybody could explain how a digital audio snake works, and if possible, how the fibre connection running to the OB vehicle is then converted back from digital to analogue. Does the snake connect straight to a digital desk or is the a D/A converter which converts audio back to XLR cables and Line feeds? Do Digital snakes split the audio themselves into seperate fiber optic cables? As you can probably guess I'm quite lost on the whole subject and hoping theres someone out there who can ease my confused state of mind. Thanks a trillion to anyone whos taken the time to read this, and I look forward to any advice which could be offered on the subject. I'm also sure that if anybody could offer an explanation on how these systems work then many other people would benefit from the knowledge. All the best, James

[-Noodles-]

A quick google search;

"Category 5 cable includes four twisted pairs in a single cable jacket. This use of balanced lines helps preserve a high signal-to-noise ratio despite interference from both external sources and other pairs (this latter form of interference is called crosstalk). It is most commonly used for 100 Mbit/s networks, such as 100BASE-TX Ethernet, although IEEE 802.3ab defines standards for 1000BASE-T - Gigabit Ethernet over category 5 cable. Cat 5 cable typically has three twists per inch of each twisted pair of 24 gauge copper wires within the cables."

from Wiki, about Cat5 cable.

And also;

Cat 5E Cables and Armoured Cat 5E GSWB Cables

[James_uclan]

Thanks noodles, you've managed to explain what a Cat 5 cable is. That bears no relevance to my question, which was about how a digital snake converts digital signals back to analogue, preferably to connect to the wall box of an outside broadcast unit. If the answer was as simple as performing a 5 second Wiki search I would not be posting on this forum.

[klaukholm]

Welcome to the forum!

Originally Posted by James_uclan

I'm currently doing a dissertation on Outside Broadcast and the last part involves writing about linking audio via splitters and audio snakes to the OB van, the FOH desk and onstage PA.

Is this really for a dissertation? It seems an unusual topic for a doctoral dissertation.

I think internet forums are inappropriate sources for academic papers in general as your sources are unreliable, and proper citations become difficult.
For academic use, you will have to confirm the identity of the answering posters and get their consent for quotations. It is also good form to state the school, program, degree and name of your advisor.

I am sure you will get pointers to the appropriate litterature here from our fellow forum members

[klaukholm]

While it surely varies from country to country, there is no standard in play.
Both optical and coaxial MADI is common for the audio, and there are some proprietary solutions out there.
Some solutions are emerging, but have not caught on as of yet. These include Hypermac and Supermac. There are also optical fibre solutions in play for video.

[James_uclan]

Hi Klaukholm, yes I'm currently doing a dissertation on Outside Broadcast setting up an event such as Glastonbury for my 3rd year FYP. Although I've found alot of sources providing information about digital snakes, including receiving some useful information from an engineer working for SIS (who cover glasotnbury and recently bought BBC's OB fleet in 2008), I am completely baffled as to how a digital audio snake actually works. I have alot of useful articles explaining the advantage they present in cutting out RF interference which can occur in carbon based multiplex cables such as Star Quad, and have been pointed to a few manufacturers websites, including telecast fiber etc. However, although I have been able to read about Fibre snakes and look at diagrams, without actually having had the oppurtunity to use one before I do not understand the mechanics behind how they work, I am hoping if somebody could explain the how an audio snake is put together then I will be able to read over the manuals again and make sense of the system, which I'm sure would be quite simple to understand if I were able to gain hands on experience, which unfortunately I cannot do. There is a diagram showing the standard set up of a Light Viper digital audio snake, in which the XLR cables on stage are plugged into an A/D converter which then sends a feed via fiber optic cable to both Front of house and another fibre connection runs to a split, in which I am assuming seperate fibre cable can be connected to transport audio to an outside broadcast vehicle, mixing desk for recording etc. However, what I don't understand is how this would be connected to the outside broadcast vehicle. I would have assumed the signal would have been converted from digital back to analogue, with seperate XLRs able to connect to the wallbox of the OB vehicle, however I have not seen any D/A converter and am therefore quite confused.... to give you a better idea, the diagram I have explained can be found here: http://www.lightviper.com/documents/...l%20System.pdf Once again, if anyone can help to explain i would be most grateful as I seem to have hit a brick wall. Thanks again for taking the time to read, James

[matthewd]

Hi there

Your missing link may be the MADI stream that travels down the fibre or bnc. The A-D is at the stage box end of things and the MADI signal containing 56 or 64 channels of digital audio at 48K usually goes straight into a digital desk, hence no D to A at the control room end. RME is a useful source of info on MADI. There are other formats and protocols but this is a common one at the moment.

Matt

[TC Custom Audio]

Dude, most of these systems are proprietary. You've got SuperMac (AES50) and HyperMac used in the Midas digital systems. Then there's CobraNet and whatever the Aviom system is based on, etc.,etc. Most of these protocols impliment CAT5/CAT6 or fiber. But, the protocols are not interchangeable. Digital splits are basically closed systems (probably, more accurately described as networks). If you buy the AVIOM system, then you're using AVIOM. You need that gear on all ends of the system, delivering audio to FOH, Monitor, Broadcast truck, etc.

Given that you're talking about technology that is not really standardized (not like TCP/IP or something), I would suggest you go directly to the manufacturers. They all have websites that describe their products.

[TC Custom Audio]

No D/A? Are you serious? Between all of the products out there, you can get a digital snake that will deliver audio in whatever format you desire, whether that be analog, AES3, MADI, etc. I don't think you quite understand what these products are for. This is basic.

[James_uclan]

I think this may be making sense. Just to be sure I understand correctly -- all analogue feeds are connected to a A/D converter, the signals are sent via fibre wire to each area where they are then connected to a digital mixing desk. If I'm correct please let me know. I'm used to connecting all audio feeds to a mixing desk through a control panel in an engineering room, taking the patch used in the studio and linking it to the correctly numbered patch for where I want the audio to be sent on the mixing desk. If all audio is sent digitally then I guess the fibre link is connected to the OB unit via a single fibre port which links to a digital patching device inside (removing the need for analogue links) - and then sent to a digital audio desk? If somebody could confirm my thoughts it would be much appreciated, as if i know this is the correct theory this means I can go on to research into all the relevant equipment. After researching all the links I could even leave a post on this forum explaining setting up a digital snake system, as if anybody has been as stuck as I have become with them I know it could come in quite useful. Let me know what you think. All the best, James.

[klaukholm]

A very basic snake is what we have here.
It is a Euphonix analogue to MADI converter (just a plain AD with madi output)
In the other end i can hook up the MADI to analogue converter.
In this case I have 26 analogue xlr channels going in on one end and 26ch xlr analogue coming out of the other.
I can place a MADI to AES converter at the end and get AES output instead of analogue.

One can place a madi router in between these units and you can the route to additional madi optical or coaxial, AES, etc.


note: I would still not use the word dissertation above, as that is reserved for PhD, DMA or similar doctoral degrees and is not used in reference to Graduate degrees or lower. By FYP, do you mean final year paper?

[James_uclan]

I think using the analogue conversion would make more sense to me. I'm going to look into in a bit more depth on the telecast fiber system as this seems to be what SIS are using. And as far as I'm aware we've always called it a dissertation at my university, I wasn't aware that definition was reserved for Phd's etc. Cheers for the help, James

[MikeV]

Originally Posted by James_uclan

Thanks noodles, you've managed to explain what a Cat 5 cable is. That bears no relevance to my question, which was about how a digital snake converts digital signals back to analogue, preferably to connect to the wall box of an outside broadcast unit. If the answer was as simple as performing a 5 second Wiki search I would not be posting on this forum.

It was just a bit of information and should still be appreciated; he took the time to do it.

[BenFranske]

Originally Posted by James_uclan

Does the snake connect straight to a digital desk or is the a D/A converter which converts audio back to XLR cables and Line feeds?

Could be either way. The thing about digital snakes is every manufacturer does it differently. Well, I guess there are a few competing standards plus a lot of proprietary stuff. You could run it straight into a digital board (assuming compatible interface), you could run it into a D/D converter which outputs AES and then into a digital board, you could run it into a D/A converter and then into anything you wanted.

Originally Posted by James_uclan

Do Digital snakes split the audio themselves into seperate fiber optic cables?

Not all digital snakes use fiber optic cables. Many use CAT5 or BNC sometimes running an entireley proprietary signaling system, sometimes over Ethernet or TCP/IP and sometimes a combintaiton of any of the above. In the case of fiber optic digital snakes the manufacturer might make a separate splitter box, they might be daisy chained or the stage box might have multiple outputs.

The only sure thing about digital snakes is there are no sure things every one is different.

[James_uclan]

Cheers for explaining the different options available Ben, its much appreciated. All this information has been extremely helpful, as I'm now able to visit the manufacturers websites and peruse through their equipment without wondering how the whole system connects and have also been able to research into the different types of audio conversion methods mentioned such as MADI etc. I apologise for my reply to noodles, at first I took his reply as sarcasm however I realise he was only trying to help. I'm sure if I'd had the oppurtunity to use a digital snake before then the whole system would make sense alot faster than it has reading about it, however with everyones help everything is finally clicking and I've found myself able to continue writing the end of my Final Year Project.