Alan Sallabank takes a look at the (unintentionally confusingly named) MOTU HDX-SDI.

MOTU's website says...

Putting the Audio back in AV...
Capture and monitor up to 16 channels of audio (analog, AES/EBU or Embedded) at sample rates up to 96kHz. Employ Sony 9 pin machine control for advanced Batch Capture and Edit To Tape operations. Keep everything frame accurate using time code and video reference.

Introducing the MOTU HDX-SDI

Here's a little product that's really unknown in the audio world, mainly because it's primarily marketed as a video only device, and doesn't list Pro Tools as compatible.

Given that it has no Mic Amp, or MIDI, you'd be forgiven for ignoring it.

But if you're running a Post Production Mix facility with surround sound, especially on Windows, then this might just be the device for you. It has HDMI and HD-SDI inputs and outputs (with up to 8 channels of embedded audio), 8 analogue inputs and outputs, 8 AES inputs and outputs, Video Reference and LTC inputs and outputs and a front panel headphone output. 

Why especially with Windows? Well, when it was first launched it was one of the first Thunderbolt audio devices, AND fully compatible with Windows (with a Thunderbolt installation). Because it's primarily designed for use with NLEs such as Avid Media Composer and Premiere Pro, it is more than compatible with Windows, post Pro Tools 11, when they introduced the Avid Video Engine.

Installation

Let's take a look at the practicalities. First installing the drivers from MOTU....

On plugging in the Thunderbolt to my X99-A Thunderbolt equipped Windows PC, and turning on the HDX-SDI, the following comes up -

And once you select the correct autoconnect settings, Windows confirms it's happy -

Now this is where things get a little tricky if you have more than one video peripheral installed.

When they integrated the Avid Video Engine in to Pro Tools, maybe Avid's developers never thought that there might be an installation that has more than one video peripheral attached, so never wrote in the option to be able to select which device you want the AVE to output to. It appears to work in alphabetical order - if I have an AJA device connected as well as my BlackMagic, Pro Tools will default to using the AJA. If I have my BlackMagic attached at the same time as the MOTU, Pro Tools defaults to the BM. In the case of the AJA or MOTU I can simply disconnect them from the Thunderbolt, but my BM is PCIe, so I have to go the hacky route of disabling it in Device Manager, then rebooting Windows.

An Apple A Day Keeps The HDX-SDI Away?

Those of you of a fruity persuasion will have by now noticed that I'm banging on about Windows. There's a good reason for this. I had hoped to be able to do a direct AB comparison between my MacBook Pro and my Windows machine, both running Pro Tools 12.4HD and connected to the MOTU via Thunderbolt. However, my MBP is currently running Yosemite, and it seems that MOTU driver development for the HDX-SDI stopped at Mavericks. Unlike Windows 10 which seems happy on the whole with Windows 8 drivers, Yosemite won't recognise the MOTU device, either as a video peripheral or as an audio device. Which is a massive shame. More about this later in the summing up. 

Using the HDX-SDI

The MOTU Video app gives you all the options you'd expect from a video peripheral. 

You can choose the usual selection of video formats, and there's a neat little audio patchbay to choose which of the 16 outputs go to analogue, AES or embedded HDMI.

Pro Tools allows you to select the MOTU PCI Video ASIO as the playback engine, and off you go.

So far so good, and to the untrained eye, the video playback seems steady and responsive. The sound quality is what I'd describe as average - perfectly good enough, but not quite as good as my RME.

Test Results

This is where we start to see something alarming happening.

At the beginning of the test, it is very impressive - the latency seems constant and very consistent, but then after about ten seconds, it gets progressively further out of sync. This happens on every playback.

Maybe it needs a video sync reference? If it did, I can't find any way to then get this into Pro Tools.

Conclusions

I had really high hopes for this unit. On paper it's an incredibly handy and competitively priced device, with Thunderbolt and the ability to output embedded HDMI, which I was especially interested in. I wanted to get a HDMI preamp, to be able to directly compare my Pro Tools output with DVDs, BluRay, even off-air, and have the preamp look after sync compensation using HDMI Lipsync. That would be fine, if I could trust the playback.

I was not able to get Pro Tools to see any of the machine control functions, the video sync reference or the timecode section. It seems that Avid have this sewn up with their SyncHD.

Legacy?

I am also concerned that MOTU now treat this as a legacy unit. You could understand why - tape acquisition and delivery are very much on the decline nowadays. AVB is also upon us, but I have yet to find an AVB video interface that would directly interface with Pro Tools. There is a lot of specialist AVB video equipment around, but nothing specifically audio related.

There is also no support for Apple users on anything later than Mavericks. It's not just a case of being unsupported, it won't even recognise the unit.

Looking Forward

I am guessing that it really hasn't occurred to MOTU that this unit, or a modern revamp of it, could be very desirable to Pro Tools users.

MOTU - If you do a revamp, I'd suggest a video playback only unit, still with Thunderbolt (though maybe also add USB3), with the ability for all the audio outputs (including the HDMI embedded) to be available to an AVB stream and patch matrix. Maybe even chuck in a couple of Mic amps and some MIDI. Now that would be wicked.

Equipment Used 

• Asus X99-A with Intel i7 5820
• 16GB DDR4 RAM
• Nvidia GTX660Ti GPU
• Samsung 850EVO System and Media Drives
• Thunderbolt 2
• RME Fireface 802
• Windows 10 Pro 64bit
• Pro Tools 12.4HD. Eucon 3.3.2.