[linux-audio-user] IP audio transport

[Dan Mills]

On Friday 16 September 2005 15:32, Matt Rockwell wrote:
> Greetings,
> I am new to the list and linux audio as I have taken over engineering a
> radio station.  We will be building a brand new studio on campus in
> 2008, and I have already started to meet with the architectural
> committee.  The more I consider our mission and where broadcast audio
> has the potential to go in the future, the more I find I would like to
> implement an open architecture infrastructure for the facility.

Ahh broadcast, something I know about.

> At this point, one of the largest questions I am facing is the transport
> of the audio around the plant, and potentially around campus.  The UW
> has invested a tremendous amount of effort in building a multicast
> capable infrastructure to handle communications needs of the campus into
> the future, so we will certainly have pipeline available if we wanted to
> get data from point a to b.  The question is what type of transport
> would be capable of interfacing with what type of in-house switching and
> routing?

I would be looking at pulling a **LOT** of ethernet cable, and leave the final 
decision as to what the protocol will be until nearer the time. 

There are really two reasons for this:

1: Your requirements **WILL** change over that period, for example, it might 
be that you end up needing more remote inputs from an on campus venue, and 
need lower latency which would at the moment favour ethersound over cobranet 
IMHO. 

2: There are several competing technologies at present and it is not at all 
clear to me which will become most common in each market for example, apart 
from the obvious Cobranet and Ethersound there is the Axia audio stuff which 
is aimed squarely at broadcast as is the Arakis product (amongst others), 
maybe SAS will bring out something useful....

One tip, if you are specifying network infrastructure, have them wire it with 
foil screened cable, that way, if you need to run a quick and dirty feed to 
somewhere, you can just use the network wiring to carry line level audio.  

Ohh and put some coax runs from your rack room to each studio as well (word 
clock and possibly video feeds).

As new as all this stuff is, I would wait a year before getting too detailed 
about what to hang on the end of the cables, the technology will be much more 
mature in a year and it will be far easier to find product that is a good 
fit.

> The in-house needs would be a system capable of replicating something
> along the lines of what Z-sys:http://www.z-sys.com/pp_routing.html
> equipment is capable of providing.  My first choice would be to
> replicate this type of routing in software as well [JACK on a large
> scale].  The question then leads into what will be the transport
> method?  Cobranet http://www.peakaudio.com/CobraNet/Background.html is
> certainly promising with actual market availability, but it is still
> proprietary.

Ethersound has the same problem, but also does distributed routing and uses 
standard ethernet layer 2 hardware. Give it a year, then attend NAB and 
possibly IBC.

> I ultimately envision a system where an artist (DJ) sits at a terminal
> and has the capability to patch their own inputs with ALSA and JACK,
> bring everything up on a control surface for tactile use, and route to
> air, stream, or file.

The Rivendell mob are working on it (Disclaimer, I am one of them)! 

The patching is probably best not handled at the DJ level at all, why not just 
have everything hooked up to a router all the time and just select what the 
control surface channel -> router mapping is. That way all the heavy lifting 
can be done in the rack room, and you get the vast majority of the heat load 
out of the studios. 

On that subject, don't forget to slap the mechanical design team around about 
noise transmission from ductwork, they never understand why this matters! 
Also make sure your rack room has ample cooling for everything you might ever 
possibly want in there...

A Raised floor in the rack room is **GOOD**.

The rack room cooling needs to be on the protected power supply, if the aircon 
goes down with the mains supply, you are off the air in short order even if 
the racks are on a UPS/Generator combo.

Talk to IT about experience in server room design, it is pretty similar for 
the main rack room (Buy them scotch, it usually works).

Ohh, run some (lots more then you need) ,N type terminated cables from the 
rack room to the roof, these are useful for whatever random RF needs you 
have. say you need a new sat. downlink, or need to monitor for a emergency 
broadcast system feed, these will be useful. Use good cable for this, I like 
Westflex 103 if the run is not too long, of one of the smaller andrews cables 
if it is.  

Just my random thoughts on broadcast... Your milage may differ.

HTH.

Regards, Dan.