Brief Summary

In this article James Richmond shares how in spite of having some premium gear, because of the way the DADman control software handles multiple interfaces and the AX64’s connectivity and comprehensive sample rate conversion it was the DAD AX64 which solved an intractable problem in his studio.

Going Deeper

When Digital Audio Denmark (DAD) announced the AX64 almost a year ago, alongside its petite sibling the Core 256, it marked a significant change in high end, high channel count digital converters/audio interfaces. The earlier AX32 and Avid MTRX interfaces (the latter made for Avid by DAD and largely the same product with the addition of a pair of Digilink ports) had been a complete success, setting a new standard for audio connectivity and interoperability. 

Both these interfaces lacked one important feature, a connection to the host computer via Thunderbolt, PCIE or USB. The AX32 relied on a 3rd party solution over (Dante, MADI or AES) and the Avid MTRX afforded the same choices plus connection to Avid HDX or HD Native cards.

The AX64 and Core 256 both feature Thunderbolt 3 connectivity using a low latency driver dubbed ‘Thunder |Core’. DAD have massively increased the channel count in the base units, with 256 channels of Thunderbolt IO, 256 channels of Dante. The summing processor is now 64 Output / 512 Input busses too. Finally SPQ speaker processing is now built into the units, with 1024 filters combined into 64 channels with 16 filters. The rear panel 16 channel AES/EBU connectors have been replaced with 16 channels of ADAT IO.

What I Need In An Interface

I work primarily as a composer and musician utilising a wide variety of instruments; guitars, bass, drums and percussion, various synthesisers especially modular synthesisers. I use a lot of input sources and a fair amount of outboard effects and processors when writing and mixing. As such my minimum interface channel count is 64 channels, but ideally needing 128 without having to re-patch. This might sound like a lot, but when you consider that just my main modular synthesiser system alone has 16 outputs then it starts to make sense.

The great advantage of Dante as a recording technology is its scalability and how it can be routed. I’ve become used to the luxury of having a separate input to the computer for every source. I am also working fairly equally in Pro Tools and Logic, composing and tracking in Logic, tracking and mixing in Pro Tools. 

My requirements for a native audio interface really are compatibility with Dante or MADI and either a PCIE or Thunderbolt connection, plus a large enough channel count to allow channel parity between HDX and native, so that everything can be labelled the same. I also need rock solid driver support and top tier analogue to digital conversion & clocking.

I have used the Avid MTRX as my primary audio interface since 2020 and it has been fantastic. As an audio router/hub/monitoring solution it has no equal. I use Pro | Mon to manage speaker sets and input sources, route audio between different places, monitor input sources from hardware.

Given I currently spend 50% of my time in Pro Tools and Logic I have additionally needed a native audio interface that could be connected to the MTRX. For most of this time I’ve been using a Focusrite Rednet PCIER card which gave me 128 channels of native IO in a 2019 Mac Pro. This combination has worked well, but a move to a Mac Studio Ultra meant that the Focusrite card, which is unsupported by the new Apple silicon computers, had to be replaced.

My Sample Rate Problem

For some time now I’ve been trying to figure my way around a particular problem when managing incoming session files that are in different sample rates.

Here is the scenario. My studio is fixed at 48kHz sample rate but I sometimes receive session files from clients in different sample rates. If it is a native session then it will open and the native audio interface will automatically switch sample rate which causes a sample rate mismatch between the native interface and the MTRX. 

I have two options at this point. First is to sample rate convert the session before I can hear it. Secondly, to change sample rate manually in the MTRX and other external Dante converters. 

Experienced MTRX owners will no doubt be thinking ‘why not just have the MTRX follow the PCIER card’s sample rate?’. Without getting into the detail, that isn’t an ideal situation either, mostly because although the MTRX can follow SR changes, the rest of the Dante converters do not.

None of these options has been ideal for me. So I eventually introduced a third audio interface, an Apollo X8, whose output was attached to an AES3 input on the MTRX that can do on the fly sample rate conversions. If you think this was all a bit of a confusing mess, you’d be right. Not because of any limitation in the equipment, but simply because my workflow requirements are highly specific and I work with more than one DAW.

The AX64 has done away with all of this complexity. It is now installed as my primary interface, acting as the Pro | Mon monitor controller and audio router. I have the MTRX and another AX32 slaved to it over coaxial MADI. The MTRX and AX32’s IO is served up to the AX64 over MADI and Dante. When I get a Logic session in 44.1kHz or 96kHz the AX64 follows Logic and the MTRX and AX32 in turn follow the AX64.  ‘But’, I hear you say, ‘you’ve simply exchanged the Rednet PCIER card and the Apollo X8 for two different interfaces.’ Sure, that is true, but it is all about workflow.

I must commend Digital Audio Denmark for how multiple interfaces in DADMAN are handled. Functionally there is no real difference between using a single interface with multiple IO cards and using multiple DADMAN enabled interfaces with multiple IO cards.

As you can see from the screenshot, all of the analogue inputs and outputs are shown in a single window, labelled intelligently. The only thing I need to be aware of is a small amount of additional latency (around 5-10 samples) needed to transport the audio from the MTRX and AX32 to the AX64. In short, it just works. 

Any Downsides?

Very few, I must say. I still find labelling channels in DADMAN to be a time consuming experience. I might be doing it wrong but I cannot see anyway to incrementally number a series of channels. Given the huge channel counts in these devices it would be very helpful to select a range of channels, input a prefix string and have the unit sequentially number the selected channels.  At least now key command copy/paste is supported.

Also, the substitution of AES/EBU with ADAT on the back of the unit has been a step backwards. Anyone with digital input monitors may have to shell out for the AES3 option card, as I have. This card has the additional advantage of on the fly SRC on inputs, which I have found useful.

I also find the placement of the rear panel MADI option card underneath the power input to be less than ideal. Personally I’d have preferred ADAT IO to be there, so I can ignore it.

One previously unpublished specification that I’d like to draw attention to is the ability to repurpose the AX64’s ADAT IO as 2 channel optical S/PDIF. This will be helpful to owners of Kii Three monitors and may mitigate the need for the AES3 option card in some situations.

Avid MTRX II

Since I installed the AX64 there has been an announcement from Avid regarding the MTRX II and Thunderbolt 3 option card. I had suspected that a second generation MTRX was coming, based on the AX64 and that is exactly what it is. On paper it does everything the AX64 except exchanging the ADAT IO for a pair of Digilink connectors.

There has been a certain amount of consternation in online communities regarding the MTRX II. Firstly, about its price, with the base chassis being $6999 plus $699 for the Thunderbolt option card. However, if you take the MTRX I, add in an SPQ card and two of the 128 channel Dante IO cards you’d be looking at over $11000 plus it would use 3 card slots and you still wouldn’t have Thunderbolt. I’m not sure it can be said to be a ‘bargain’; these are high-end and highly capable devices. That said, the AX64 is significantly cheaper than the MTRX II at $4999 USD.

The second concern I’ve seen expressed is around the lack of Thunderbolt support in the MTRX I. Jan Lykke from DAD commented publicly on this as follows:

“The simple answer is that it is technically not possible. The flash memory holding the firmware in the AX32 is jam-packed so there is not room for new option cards. Also, the TB3 module must be capable of delivering 2 x 15W of power, and the power supply in the AX32 is not capable of that.”

Anyone with an MTRX I who is looking at the MTRX II and is thinking ‘I’d like it but I can’t justify selling the MTRX I chassis and buying the MTRX II’ might want to seriously consider adding a Core 256 instead. At $2995 it is quite a bit more than the Thunderbolt option card, but again add in a couple of Dante cards and SPQ and you are well over $6000. Having integrated multiple DAD devices I can tell you that from my perspective they largely appear as one large interface. Once you’ve set up the channel and device routing and labelled your inputs the inter-device connectivity is essentially transparent.

Conclusion

The Digital Audio Denmark AX64 is an impressive high-end digital converter/audio interface that sets a new standard for audio connectivity and interoperability. With its Thunderbolt 3 connectivity, large channel count, and built-in SPQ speaker processing, it provides seamless integration for those working with multiple input sources and outboard effects. The AX64 eliminates the complexity of managing incoming session files with different sample rates, making it a valuable addition to any composer or musician's workflow. While there are some downsides such as labelling channels in DADMAN and the substitution of AES/EBU with ADAT on the back of the unit, the AX64 is a highly capable device that delivers excellent analog to digital conversion and clocking. With its competitive price point, the AX64 offers a compelling alternative to the Avid MTRX II and other high-end interfaces on the market.