Reverse Engineering The Behringer Ultranet Protocol

Ultranet is a protocol created by audio manufacturer Behringer to transmit up to 16 channels of 24-bit sound over a Cat-5 cable. It’s not an open standard, though: Behringer doesn’t offer an API or protocol description to build your own Ultranet devices. But that didn’t stop [Christian Nödig], thanks to a defective mixer, he poked into the signals and built his own Ultranet receiver.

Ultranet runs over Cat-5 ethernet cables but isn’t an ethernet-based protocol. The electrical protocols of Ultranet are identical to Ethernet, but the signaling is different, making it a Level 1 protocol. So, you can use any Cat-5 cable for Ultranet, but you can’t just plug an Ultranet device into an Ethernet one. Or rather, you can (and neither device should explode), but you won’t get anything out of it.

Instead, [Christian]’s exploration revealed that Ultranet is based on another standard: AES/EBU, the bigger professional brother of the SPD/IF socket on HiFi systems. This was designed to carry digital audio over an XLR cable, and Behringer has taken AES/EBU and tweaked it to run over a single twisted pair. With two twisted pairs in the cable carrying a 192 kbps signal, you get sixteen channels of 24-bit audio in total over two twisted pairs inside the Cat-5 cable.

That’s a bit fast for a microcontroller to decode reliably, so [Christian] uses the FPGA in an Arduino Vidor 4000 MKR in his receiver with an open-source AES decoder core to receive and decode the Ultranet signal into individual channels, which are passed to an ADC and analog output.

In effect, [Christian] has built a 16-channel mixer, although the mixing aspect is too primitive for actual use. It would be great for monitoring, though, and it’s a beautiful description of how to dig into protocols like Ultranet that look locked up but are based on other, more open standards.

21 thoughts on “Reverse Engineering The Behringer Ultranet Protocol

  1. Oh the hypocrisy. Behringer built their initial success by reverse engineering high end studio gear then cloning them using cheap low grade parts, and now they protect their IP using the very same tactics they fought against.

        1. That rarely stops companies from threatening or filing suit. Merely going to court to ask a judge to dismiss a frivolous lawsuit costs money. It’s almost as if our legal system has been captured by capital… *suspicious emoji*

    1. Sure they made kit cheaper by ripping off others designs. But I think their modus operandi has always been profit. Now I would say they have grown up and started to make original designs (or acquire) and not make it easy for others to replicate. What we need are more standards…… my Midas m32 now supports aes50, Dante, madi, (the usb audio codec thingy I can’t remember the name of), and ultranet deffo need more standards to add to the list.

      1. “But I think their modus operandi has always been profit.” – that is the same for “high end studio gear” manufacturers as well

        “using low grade parts” – and that is a FUD

        Don’t get me wrong, Behringer has its problems – lots of it, but they make things affordable. I think there is one more thing at play. Before Behringer, if you wanted certain kind of sound, you was required to buy very expensive gear – or in other words, if you had certain kind of sound, it was proof that you spent a lot of money. Than came Behringer – and now “that kind of sound” is available for 1/10th of the price. So anybody can have it without spending large sums. Behringer is mostly hated by owners of expensive equipment. In my experience, people who can’t afford expensive equipment kind of likes Behringer – or at least doesn’t hate it – because they can at least have it.

        (and yes, their CEO is douchebag – they are not the only company with this problem)

        1. Many good points well stated. To be frank the advent of cheap and more powerful dsp’s has allowed almost any “vintage” booji’ bit of kit to be modelled. The sad part is they are now hidden behind subscription walls that i hate mere than the rip the kit off method of profiteering…. Guess im just old and grumpy. I also don’t miss lifting outboard racks and crown macrotek amps. Or analogue multi runs…….

  2. > With two twisted pairs in the cable carrying a 192 kbps signal, you get sixteen channels of 24-bit audio in total over two twisted pairs inside the Cat-5 cable.

    Something doesn’t seem to add up. A single channel of 24bit 48kHz audio would seem to need about 1.152 Mbps of bandwidth per channel. Or does the “192 kbps” just mean that the audio channels themselves are running at a 192 kHz sample rate? That’s a (somewhat) common audio rate so I suspect that’s the case.

  3. “With two twisted pairs in the cable carrying a 192 kbps signal” ….. seems a bit low for 16 channels x 24 bit quality. Would expect more like 4Mbps or greater?

    1. Each pair carries an AES-3 stream, 24 bits per audio sample, 32 bits per subframe (audio + 8 bits sync and control data), 2 subframes (conventionally Left and Right) per frame. 192000 frames per second. So each pair has 192 kilosamples per second (ksps) of stereo audio. Ultranet interleaves 48kHz samples instead, so ‘L’ is now 4 channels at 48 ksps and ‘R’ is now 4 channels at 48ksps. And that is repeated on the other pair, giving a total of 16 channels at 48ksps.
      On each pair there are 192,000 x 32 x 2 bits per second (12.288Mb/s) with BMC coding, so 24.576Mb/s of actual data on each pair.
      Hope that helps with the confusion as some people are calling it 192kHz (stereo sample rate), 48kHz(individual sample rate), 384kHz (single channel effective sample rate), and 24 bit or 32 bit samples, and they are all correct.

  4. Why?

    If the same wire was used for Gigabit ethernet would 16 channels of 24-bit audio be a difficult thing to achieve?

    Is it a latency thing?

    Or is it just a way to charge audio people big bucks?

    1. It’s a latency thing, plus when you can guarantee that no proper ethernet frames are on cable, you can just output one simple signal continously, without any conflicts or anything unwanted taking up the bandwidth.

  5. What happened to the other 2 pairs in the cable? Although I’m sure that helps reduce cross-talk. Especially in cables with hard plastic seperator, can run the data on non-adjacent pairs.

    Odd though. I guess it’s cheaper to do 2 pairs at a “high” bandwidth for this kind of audio.

    Or the other pairs may be reserved for a back-link, 16 out, and 16 in channels?

    Would love to see a version with 4 or 8 (our stage only has 4 mics). The cable savings seems enormous, not to mention labor and design costs for installations, especially for mobile operations.

    1. You can run 4 aes3 stereo signals on cat5 (IEC 60958-3, I believe) but then you need to convert your analog mics at the stage end. Running 4 balanced mic-signals over a cat5 is a well-used hack, you can even buy converter boxes for it.
      Rane did a nice overview paper on aes versions called “interfacing aes and s/pdif”, but I’ve lost the link.

  6. The max number of channels is 32 inputs and 16 returns. I recently installed one of these units in our school auditorium and it allowed us to reactivate wiring that hadn’t been used in 20 years. Very slick.
    Also to be clear, 48v audio isn’t PoE. It’s a similar (but much older) standard called phantom power. It was originally designed to power condenser mics, MIDI equipment, and other audio equipment over XLR cables.

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