Aggregate devices and I/O -- not quite working


I have two different aggregate device setups.

The smaller one consists of a MOTU 828MKIII Hybrid and a MOTU 16A. This pairing produces an aggregate device with 64 ins and 62 outs. The MOTU 828 is the clock source, everything is set to 48khz. This device operates without issue in Cubase at a buffer of 256, 32bit float processing, ASIO set to normal, boosted audio priority, and a disk preload of 2 seconds. It also works without issue in my other DAWs (Logic, Studio One, Bitwig, etc.)

The larger aggregate device adds one more interface to the above and consists of the MOTU 828MKIII, the MOTU 16A, and the Expert Sleeper ES8. This creates a device with 76 ins and 78 outs. As before, the MOTU 828 is the clock source, everything is set to 48khz. This device runs fine in my other DAWs, but Cubase will not work with it. If I try to use this device with Cubase, the CPU meter overload indicator is constantly on and cannot be clicked to reset. However, none of the activity meters show any activity.

picture 1

The program GUI is responsive, but no soft synths or wav files will play; there simply is no audio produced by the system when I use the larger aggregate device and and that indicator is active.

However, if I go into Audio Midi Set Up (with Cubase still running) and remove the ES-8 from the aggregate device (making it 64in/62out again), the CPU overload indicator immediately turns off and everything plays normally.

picture 2

This leads me to believe that there is an I/O limit on aggregate devices.

Is there?

Thanks for reading this far!


EDIT: SYSTEM SPECS: iMac Pro 10 core, 64gb, macOS Big Sur 11.6.5, CB Pro 12.0

The I/O limit for Cubase itself is 256 inputs and 256 outputs.

Maybe different ASIO-Guard settings can help?

Thank you for replying!

I should have mentioned that changing the settings for ASIO Guard seems to make no difference. IIRC: I make the change, apply it, the CPU indicator is free/blank for 1 or 2 seconds, then it comes back on and stays on.

Thanks again.

Hi !

Did you find a workaround ?
I have the same issue on Monterey 12.3 .

Hey there.

Nothing yet. I sent in a support request on this and so far radio silence.

I’ve been working with the “smaller” device as well as I can given the ASIO guard issues discussed elsewhere. But that means not using any of my eurorack and tape-based gear (with Cubase at least) which is a bummer.

Thanks for the question.

Hi ! Thanks for the reply .
I have this issue using 2 RME ( UFX & UC ) .
It seems weird because it works for you with 2 MOTU .
By the way I had an ES 8 like you .
I have now an ES 3 & 6 connecting to the UC ADAT .

I really think it’s a limitation on the number of channels from an aggregate device…the smaller configuration is 64in/62out. The larger is 76in/78out. Maybe it’s going over the number 64 for IO that causes the issue.

I think I will create another device that is only 66in and see if there is a problem. I’ll post my findings later.

About the ES8: I have two older MOTU 828MK2s connected via ADAT to give me 8 in/8out on the ES-8’s ADAT ports. Works like a charm! (In other DAWs…)

Also experiencing this issue in Cubase Pro 12.40 on Monterey 12.5. Going to file a ticket. Bitwig handles the aggregate device with 4 devices just fine.


So I have changed my audio device configuration adding something’s and replacing others. I’ve updated to Cubase 12.0.40.

The problem however remains. If an aggregate device goes over 64 inputs or outputs, Cubase’s audio engine seems to stop working.

How is this handled in professional studios for goodness sake?

I’ve been in sporadic contact with tech support on this issue. They acknowledge that it exists, but have stopped responding. (To be fair, I have stopped pinging them, but I will resume trying.)

Bitwig, StudioOne and Reaper have no issues in this regard.


How is this handled in professional studios for goodness sake?

They stay away from aggregate devices. You can get easily get > 64 i/o with 2 or more Lynx devices, or DAD, or Metric Halo…

Dante can do lots of I/O if you don’t use 192 kHz
SR, you can combine products from different companies. MADI, also. More convoluted than Dante though.

Where I live, PT HD(native or HDX) is often used for high channel counts.

I have the exact opposite experience. I was involved setting up a large Dante network in a multi room recording studio and it was a pain to set up the routers correctly. I admit this was a number of years ago and maybe Dante is less finicky now, I don’t know.
MADI on the other hand is just plug and play basically.

This interested me because we use 5 sound cards (3x MOTU+2x RME) and buffer 128 with a total of 192 inputs on our MacMini M1 and everything runs without problems (cubase 12) both under BigSur and in Monterey. With Cubase 11, there was a bit of a problem with larger projects (rosetta), but now it’s fine.

To troubleshoot – what if you use the 828 and the ES-8? Or what if you use the 16A and the ES-8? If one of those setups also overload, then it’s clearly not a problem with > 64 channels in Cubase.

My guess is that the problem is in the driver software, not in Cubase itself. Cubase is tested with up to 256 channels, and a “unified device” really just looks like one device to Cubase – all the merging magic happens in the driver software.


Thanks for your suggestion! But I have troubleshot this pretty extensively both on my own and working with Steinberg tech support through a few email exchanges. (They recognize it as a ‘bug’, but as to where it is on the priority list, who knows…)

I’ve tried various combinations of aggregated audio interfaces. Any combination that goes over 64 inputs or 64 outputs and Cubase’s audio engine falls over.

There were earlier comments from others about Dante, MADI etc. Those technologies are great. In an effort to get around this problem, I upgraded all of my interfaces to AVB compatible devices (MOTU), bought a couple of switches, etc.

I have run into a bit of a wall implementing it. (I’m still learning how to set up and route things, insure the physical IO shows up as destinations in the DAW, etc.) One day, I’ll have my ‘aha’ moment with it I’m sure. :nerd_face:

Until then, it’s still an aggregate device for me. As was said “Cubase is tested with up to 256 channels, and a “unified device” really just looks like one device to Cubase…” The aggregate device should work. If it doesn’t, it might point to some other more important issue in the code. (Or not.)

But I do want to put it out there in case others are having similar issues.

How do you have the interface’s connected? via AVB? Aggregate devices with TB or USB direct connections? Really curious…

We use Motu 1248 and 2x Motu 24Ai via AVB switch and ethernet to the computer and 2x RME Digiface via USB2 (each to a different HUB). This way everything works without a problem. Unfortunately, TB on the Moto supports few channels and USB even less, so this solution turned out to be the best in terms of price/performance/reliability. In the foreseeable future, another Motu 24Ai will be purchased for additional inputs, so hopefully there won’t be a problem.

Thank you so much for the reply. If I may ask another question because this is precisely where I ran into an issue…

We use Motu 1248 and 2x Motu 24Ai via AVB switch and ethernet to the computer…

I have the IO jacks of my interfaces running to patch bays. (I use the patch bays as a “thru” to simply bring the IO jacks on my interfaces “to the front” of the desk where I can plug things in or out without having to crawl around.) And of course, to make my aggregate device, each interface is connected via USB or TB to the computer.

This works like a charm (except for the 64 IO limitation I’ve mentioned). I can run external effects and guitar pedals with ease, freely change my set up, etc.

To get past the apparent 64 IO limitation of aggregate devices, I tried a set up where all interfaces (MOTU 1248, 828ES, 2 16As) were connected to a MOTU AVB switch connected to my computer via a CAT6 cable . Just one device (1248) was physically connected to the computer via TB or USB.

As I recall, all of the input and output channels showed up in the MOTU matrix router just fine. However, the ONLY inputs that showed up in Cubase’s STUDIO SET UP > AUDIO SYSTEM were those from the device that was physically connected to the computer via TB or USB.

On the one hand, this sort of made sense…how could you choose to send signal to the input of an interface that was not “connected” to the computer? On the other hand, it made NO sense, because I thought the AVB network is supposed to be providing the connection via Ethernet.

I pondered this and tried a bunch of different things before deciding to go back to my trusty aggregate device setup. I figure there is a simple, but fundamental thing about AVB that I have wrong here and, over time, I will figure it out.

All of that being said: If in your experience you see something that I am obviously doing wrong or that I am fundamentally misunderstanding about the concept of AVB, please feel free to let me know. It would be much appreciated. (No worries if you’d rather not.)

Thanks for reading this far.


Which iMac? Does it support AVB?
Network cards need to support it. It’s not like Dante.
Does it work with one device?

Thanks for the question:

iMac Pro, 3 GHz 10-Core Intel Xeon W
64 GB 2666 MHz DDR4
Radeon Pro Vega 56 8 GB
10 Gigabit Ethernet (10GbE)

It’s AVB compatible …

Who said that? Which software do you use for AVB I/O?