Gotham Labs: Building a PoE Production Audio Recording Rig

Peter Schneider and Joe Orr Mulica take you through a sample cart rig using Power over Ethernet  and the Dante protocol to send audio, power, and telemetry from the sound cart to set and back via a single Cat5 cable. 

PoE Demo Schematic (pdf)

Equipment used:

Other relevant links:


Joe Orr Mulica: Welcome to Gotham Sound TV. I'm Joe Orr Mulica with Peter Schneider.

This week we kind of want to dig into something a little deeper.

A lot of times we show a product and it allows you to kind of see what that product does, how it works, and then how it can be useful to you.

This is kind of our first iteration of something we want to call Gotham Labs, where we dig a little deeper into some of the problem solving that our customers come to us with.

Peter is our head nerd for that and takes a lot of phone calls from people saying, "Hey, I'm on set and we need to do this. How do I do that?" and we go, "Hmm, interesting." We integrate a lot of different products to solve those problems.

So, with that, what's our first problem we're digging into?

Peter Schneider: So the first problem is - and thanks for that introduction by the way - but the first problem we're digging into is something that I came across.

I was part of a job- communications for a TV show called Lost in Space, constantly running coax out for their communication signals between the receiver and the transmitter. It was 150 feet for each leg times three.

JOM: This was a show with eight actors that could be on set at the same time. They all had transmitters on, but also receivers to hear.

PS: Yeah, giving them all mix minuses.

They were big sets with lots of heavy machinery running over the coax. Every time you run over coax with something, you deform it a little bit. It was a problem, and we constantly had to chase chase stuff around.

It really sort of inspired me. I started thinking that the transmitters were Dante transmitters - they were Lectrosonics M2Ts. Could I power the transmitters over the same Dante signal over that same Cat5? Could I have receivers and power those receivers and get the audio over the same Cat5?

So that was the problem that I started to think about, and that's what we're going to talk about. We don't have an actual application for this, but I think the goal is to inspire anybody crazy enough to watch this video. Not just end-users, but also manufacturers, hopefully, because I think what is on this table has a lot of potential.

JOM: So one of the things that we were just talking about was eliminating some of the coax, some of these 150 foot runs.

PS: It's obviously desirable; 150 feet of coax times three runs of low loss coax - that's very expensive. It's very heavy. It's very fragile. Replacing it with a single 150 foot run of Cat 5 is desirable because it's cheap and light.

JOM: You can get it anywhere if something breaks.

PS: Exactly. So what I've put together on our left side would be a kind of sound cart and I'll talk about why I think of that as a sound cart. Think of this in terms of functional, not literal.

Then we have the Cat5 in the middle. This could be any legal length of Cat5, so up to 100 meters.

Then on the right side of the table over here would be something ideally put in a single rack mount case, pigeon/pancake, light stand - remote it out to set.

JOM: Right, so this is your on-set and this is your run to keep the receivers close to the talent. But then here's all the audio telemetry back there.

PS: Right. So here's our Cat5 between that we do that with. So a couple of things:

The way we're gonna do this is we're gonna have a laptop simulate an audio recorder. If we switch to the laptop screen for a second, let me just pull up Dante controller, so people can see what's in our Dante network.

I think it's it's worth stating that this is doing it via Dante; this is not like getting analog audio through a balun and keeping it analog audio over Cat5; this is "can we have something remoted on-set that generates a Dante signal," and then have it be Dante over Cat5.

So this is our Dante controller. What we've chosen, if we look at our Dante transmitters here, I'm just going to double click there - that's an A10-Rack. And if we just switch to the wide shot, this is the A10-Rack from Audio Limited.

We'll do an insert of the front so we don't have to flip everything around. But the A10 rack - for those who are not familiar with it, tune into our video we did a couple of weeks ago - but it is basically 4 slot receivers and a Dante converter and RF distribution over 12 volt DC.

Immediately, I was drawn to that device because it has the ability to do 8 channels of audio and it's got the analog to Dante converter built into it and it natively runs over 12 volts.

JOM: Perfect for a sound cart, very robust in terms of being in the field, and sets it apart.

PS: Right, so just functionally, and we'll have a diagram for you guys to see. But functionally right now what I've accomplished is I've taken my Audio Limited rack and I filled it with - in our case - it's two Audio Limited receivers and then a Wisycom and Lectros, whatever we had lying in the rental bins.

But some very special advantages when you use it natively with Audio Limited, which I'll get into in a few minutes. And I've remoted it up to 300 feet, a hundred meters away from the sound cart. And now I have to figure out a way to power it. Right? Because right now it's just dead- just on near dead.

So that's where we get into this technology called power over Ethernet. You'll see it abbreviated as PoE, and some people call it Poe. I don't quite think that's right.

Now, anyways, I come from tinkering from computers, so I don't know all of the specifics of the tech terms. power over Ethernet in my mind is like an umbrella term that can refer to any method of combining power and data over an Ethernet cable.

There's lots of ways to do it; I went with the way that stuck to industry standards. There's actually codified standards for power over Ethernet.

I think the latest standard, if anybody is really going deep, is 802.11.AT. So I wanted to stick with those standards, and when you stick with those standards, you can't just - like, some implementations are dumb. There's 8 conductors in the Cat5 cable; they reserved some of them for data and some for power, and they just blast the voltage down the line.

I didn't want to do that because sets are volatile places; somebody runs over your cable, causes a dead short- that's not good. I want there to be sort of known off-the-shelf standards that take care of safety. So part of this power over Ethernet to standard is that it doesn't just turn on the voltage.

JOM: Right.

PS: There's a device on the far end that has to negotiate how much power it needs and there's a device on what I'll call the sound cart end. And that has to understand that negotiation and then supply the appropriate amount of current and voltage.

Let's talk about voltage. Things in our world run on 12 volts. Ohm's law comes into serious play when you're dealing with 300 feet of cable, so Cat5 is typically 22 gauge, something like that. Running 300 feet, you're talking about a serious voltage drop if you start with 12 volts.

So part of the standard is that it ends up at 48 volts and I think it actually starts at 54 volts on the source side in order to accommodate-

JOM: For that loss.

PS: Right. So let's start to get into some of the specifics of how we did this.

Power over Ethernet is typically supplied by switches. It's not always supplied by switches, but typically supplied by switches. Now one of the challenges that I came across was switches that supply power over Ethernet. If you're an electronics designer, the simplest way to implement it would just be to have a 54 volt input on it.

And that's sort of what you work with to send it down the Cat5 with some electronics in-between. That's not so film-set friendly. I wanted to find a switch that's 12 volts natively, and then kicks it up to the standard. And so that's where the CamSwitch 4 Mobile comes in.

And so this device: it's a little gnarly; that's not typically what you'd see on a location product, but that's the 12 volt power input. It's actually pretty cool. I think it takes 10 to 30 volts in and it will kick out - I think it even says - the standard 802.3AT power over Ethernet switch.

So it'll take 10 to 30 volts in DC and then is part of this standard. You can see it's built fairly robust, it's got a big heat sink, and it's pretty cool. This is also acting as our Dante switch.

I want us to take a slight diversion. One thing you'll notice about this switch is that it is not a gigabit switch, so I just want to dispel the myth that you must always have a gigabit switch for Dante.

JOM: Ok.

PS: This is 100 megabits. They're working on a gigabit switch version of this. It'll show up down the line in a few months. But for 16 channels of Dante audio, you don't need gigabit, so this is perfectly fine for kicking audio around most of the sets that we're talking about.

If we follow this blue cable, it goes into just an etherCon barrel adaptor into our etherCon cable. Follow that to the next barrel down the line over to here and the first thing we come to after the Ethernet cable is this. This is an 802.11 power splitter and what this is doing is taking in 48 volts.

It negotiates for the proper amount of power and it's splitting out. It's set to 12 volts out of this connector.

JOM: So we're coming all the way from 200 feet away, we've come across our Cat5, we've gone into this. It has now negotiated the voltage.

PS: I've set it here splitting out 12 volts and this is the Dante signal. So, single Cat5, data, power. From the power, I have it going into this power distribution here. And you can even see because it's got a handy voltage meter.

I have power going to the A10 receiver here, power going to the A10 receiver here, and then I'll talk about this device in a second; that's USB powered. Following the signal chain, we have our A10 receiver here, and it is getting power through this PSC box. And it is spitting out Dante right in the back. That, of course, is going back.

It's also because Audio Limited have included a way for the receivers to give data. It's got the capability via USB because remember, they imagined that this was hooked directly into a sound cart. So via USB, to give telemetry receiver information to a software program called WaveTool.

JOM: So you're talking about battery information, you're talking about actually seeing and hearing.

PS: Yeah, because it's Dante, I can hear it. So here's the thing, and this is really important. It's one thing for me to fantasize about having my receivers 300 feet away from the sound cart, but if I don't know what's going on with my transmitters and I don't know what's going on with my receivers, what good is that really?

It's not that helpful to be blind like that, so my other part of this equation is: how do I get telemetry back? How do I get it as if the receiver were directly connected to the sound cart?

JOM: So just as a recap: We have put power over Ethernet, it's coming into here, it's splitting our Dante power. So this is 150 feet away, it's sitting there closer to set; we're not waiting on electrics to power it. All this is being powered over this cable and then this is a bonus. This is all powering just fine; functional, but not necessarily as useful as possible.

PS: Right. So now let's talk about the bonus. The bonus takes that USB port and encapsulates it in a TCP/IP stream that goes back to the computer, because remember, the computer is just another node on this network.

JOM: Right.

PS: And it's presenting whatever that USB port had as a USB connection. So the way that Audio Limited has envisioned us using this device is right at our sound cart and then plugging a computer into the USB port and get all of the information that we need from their receivers. That's how the company has envisioned us using it.

We're sort of pushing that vision a little bit remoting the receivers, but what we have to solve before we can do that to make this truly useful is: how do we take that USB port and make the computer think it's connected via USB? But really, it's connected over Ethernet. And that's what this box does.

JOM: So in summary, because of the way this was built, it's USB. We're supposed to go right into a computer on your sound cart. Because it's not coming through the Dante protocol, we have to find a way to cheat the system, to say we're going to change USB to Ethernet back into the computer. So we're basically just changing it from USB to Ethernet back to USB.

PS: Right. So now if we switch back to the computer, that box we're talking about shows up as what's called a virtual link. It's this link here and, if we switch to overhead, it's that box there. And then switch back to the computer - it shows up on the computer as a USB device.

And what that allows us to do is run this program that is compatible with a whole host of receivers called WaveTool. Now, notice something very interesting. WaveTool is a 3rd party program, a really cool program, and I'll get into that in a few minutes, just briefly, because that's really part of this whole equation.

But you only see battery telemetry, which is there on native, and, if we switch to the wide shot, on native Audio Limited transmitters.

JOM: Gotcha. So I think we're on Lectro here, so you notice on 7 and 8 that you don't see the battery signal.

PS: Correct. You do, however, see audio. And how do you see audio? Because it's routed over the Dante. And if we check our Dante virtual sound card, which is Peter's MacBook Air, you can see that's how it sees it. And presumably, it would go from the MacBook Air. Also, it might go to a Sound Devices recorder or any recorder, Aaton Cantar, etc.

JOM: All right, so this is great. We've remoted the receivers to set, but what are some other advantages of doing that?

PS: Well I think anytime you have a long run of coax, that introduces a loss. I've been concentrating on the physical, like frailty or potential frailty of coax, but that's a loss. When you have a loss like that, you have to have an amplifier. When you have an amplifier, that introduces noise, can introduce overmodulation, all the sort of disadvantages that go along with that can be eliminated when you put the receivers close to set.

That's a very short run of coax cable, maybe 2 or 3 feet. I mean, there's a huge amount of advantages, similarly. Like, this being New York, a lot of times three-story walk-up is your location; you may not want to shove the whole cart up the stairs. So traditionally, you've run coax, gotta put it through a window or get ridiculously tall stands, which is what we had in Vancouver, with a ton of sandbags on it.

This lets you have one Cat5 cable, you could just cut the ends off. if you want to be sort of unsavory about it. It's not precious; you're not worried about it being cinched in the window or something accidentally.

JOM: So you're down on the street, this is three stories up. You've got your third on set monitoring what's going on so they feel connected, in the loop. And you're down on set, down on the street, remoted and as happy as a bee in your tent.

PS: That's exactly the advantage.

JOM: There's some things on the sound cart side we haven't talked about to connect it. And that is: now that we've come from the sound cart to the remote location of the receivers and now back: how do you route that? We would need a switch of some sort, right?

PS: Well, it's the same PoE switch. So, if we switch to the overhead, we could plug our Aaton or 970 Dante recorder right in there. So that's basically it in a nutshell, but once you sort of get into this program, this program actually is pretty cool.

In terms of battery information, right now in this configuration, through the A10-Rack, it only works with Audio Limited transmitters and receivers.

JOM: Right.

PS: It'll work if you added to this rack a Lectro Venue, which you could power over Ethernet. But then you don't get the Dante, which is why I like this rack. It'll natively work with the Venue too and stuff like that.

JOM: So you could use this with them, pluses and minuses with everything we do.

PS: Right, but in this particular configuration, I can monitor audio from any of the channels that are getting a signal. And I can route the audio either into the computer, or since we're geeking out, I am routing it to this Dante PoE powered headphone amplifier.

JOM: So this is bonus number 2?

PS: This is bonus number 2. And so, this could be a station at the cart or whatever and a third could be at the cart and just sort of listening to...

JOM: Are you able to mix that down or are we just hearing 8 channels?

PS: On this one, it's just solo, whichever you choose. But this program also has a really interesting feature, which is, if you hook this into a router, now we can go to any iOS connected device. We have an iPad on the table and I can see audio coming here.

If it's an Audio Limited transmitter, I can see the battery information.

JOM: So I've got my iPhone or whatever, I'm wiring somebody up...

PS: I mean, it's streaming audio, so I can go to wire you up, I can make sure your battery's good. And then because it's streaming audio, I can listen to your mic.

JOM: Right. You're listening to me. What's the latency on it?

PS: There's about a second of latency snag, half a second maybe.

JOM: Check check. Oh, not even!

PS: It's a good tool. Okay, look, we call this Gotham Labs for a reason. This is all sort of like the beginning embryonic stages of what is possible. Part of why I want to show this and why I'm excited about it is I hope that some people watching this are inspired.

And if we haven't said it already, we have for sale all of these devices. We've set up agreements, we can sell the switch, we can bundle it with the PoE splitter. So somebody wants to experiment, certainly let us know.

But also, I hope to inspire a few manufacturers. This is pretty cool. And other manufacturers have already added PoE to devices, like Glensound and their headphone amplifier. And they have A to D converters that do that.

So I think that this is a very viable standard. I know when I was on set in Vancouver, I was really very worried about that coax cable getting damaged. I would have been a lot more relaxed if it was Cat5 that I was running.

JOM: You used coax in Vancouver.

PS: I had to. One of the really great privileges I think that I have is I have time to experiment. But obviously when you're on set, that's not a place for experimentation.

JOM: But this came out of, "Okay, that could have been better." So this is our chance to, in the interim, find something in all of these products and merge them together, to say, "All right, let's create something that will work better for that."

PS: And I think that this WaveTool software probably merits its own livestream and if you'd like to see that, let us know in the comments.

I've been in the mixer's chair, I've been in the third's chair, where the mixer's telling you "hey, so and so, his battery's about to die." And if I had a way to be proactive about it, I could've changed it at the break five minutes ago. Now I gotta run in there. That's awful. To share that telemetry information is huge.

So I think there's a lot going on here. It started with this idea of like: "how do I get away from coax," and then it sort of ended up in this.

JOM: So, that's Gotham Labs 1.0.

PS: No, beta.

JOM: So, to kind of wrap it up: power over Ethernet, a way to virtually listen and see telemetry from any iOS device, convert the Dante with power over Ethernet, and also be able to listen remotely with headphones. Did I miss anything?

PS: No, and I think all of these things can be sort of stretched into other applications. This could be an outstation for a script supervisor or video village or something like that or somebody that wants a high-quality link could be put into a speaker. Like a battery powered speaker.

JOM: Anything.

PS: Let us know if you want to see more of this stuff. It certainly gets me out in the open with stuff that I'm thinking about and working on. I appreciate you guys coming out. And Joe, thanks for helping me with this.

JOM: That's great. We'll be back with more of these things.

If you were interested in coming here and labbing something out or have some uses and you want to join us for a livestream and show us what you've done, let us know.

You can send ideas or questions to [email protected].

Visit our archive to see any videos we've produced at And follow us on Facebook and Twitter for the latest news, events, sales, and anything else fun and exciting going on at Gotham Sound.

PS: Thank you for watching.

JOM: Thanks, Peter.

PS: Thank you. I don't think you'd be happy if a bee was in your tent.

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