[LAU] MOTU Ultralite AVB - possible to configure two connected devices without 430 EUR switch?

Fernando Lopez-Lezcano nando at ccrma.Stanford.EDU
Wed Oct 17 07:34:18 CEST 2018

On 10/15/2018 04:58 PM, Hanns Holger Rutz wrote:
> hi there,
> i found a number of related threads, seems mainly @Anders Hellquist who
> is using connected Ultralite AVB, but with the additional switch.
> i'm trying to determine whether this interface or the slightly cheaper
> mk4 (which has 2 more analog outs as far as i can see) makes sense for
> my setup. i have a performance project where connecting with another AVB
> device makes sense, so i'm tempted into the ultralite AVB. only...
> - manual seems to indicate that you can maximally route 8 channels
> either way, which is a bit silly given that I can already do that
> directly with the two laptops connected and Zita running...

The UltraLite AVB supports 3 AVB streams either way. If the target AVB 
Motu card also supports AVB 3 streams (8 channels each) you can send up 
to 24 channels.

The number of supported streams varies from card to card, details can be 
found in the FAQ here:


> - also manual suggests that probably i won't be getting the web
> interface served just with USB connection, but only ethernet, so
> catch-22 if i want the two interfaces connected and not spend 430 EUR on
> a bloody specialised switch.

I think that is the case, sorry. On exotic operating systems like OSX 
there is a proxy in the driver that serves http through usb (I think) so 
you can access the configuration pages without an ethernet cable.

AVB will only work through switches that support the protocol (like the 
one Motu sells). So a normal switch will not do. There might be cheap 
alternatives but I don't know of any. Some info I just found here:


You can connect two Motu cards back to back, but then you cannot add a 
computer to the mix without an AVB switch (actually the Motu AVB switch 
has a non-AVB port where I normally connect the computer).

>isn't it possible to set up the interface
> when it's not connected to the second interface and then simply replug
> the ethernet cable? i guess the problem will be that i can tell it to
> send output channels to the other interface which is not yet visible?

I forget the exact sequence, but yes, you need to connect the AVB 
streams together by selecting from the web gui (I thin on the target 
Motu you have to select from a popup on a given stream a currently 
offered stream from another card). Once they are connected, they 
reconnect automatically if the ethernet cable is unplugged and then 
plugged in again.

> or other idea - simply use an off-the-shelf ethernet plug, then disconnect
> the laptop once the web interface is configured?

I have not tried that, I imagine it would not work because AVB will not 
go through and the cards will not see each other streams'.

As to the cards themselves...

WARNING: the latest versions of Motu AVB cards seem to break the class 
compliant driver. The symptom is that on the receiving end (a Linux 
computer running Jack) the channels seem to rotate in blocks of 8. So, 
if you are sending a signal on channel #1 and receiving it on Jack, it 
will suddenly appear after a while on #9 and then move on to #17 (if you 
have that many) so on and so forth. Fun. Downgrading the firmware seems 
to cure that problem. I have seen this in an UltraLite AVB and a 1248 
(and I think on a 24ai as well).

WARNING: Another "feature" lost on an upgrade to the latest is the 
ability (on some cards, 16A, 24ai, 24ao) to have three usb modes, one of 
them enabling you to use up to 64 channels on usb2 if the sample rate is 
restricted to 44.1 and 48KHz. I have had to downgrade cards to be able 
to keep using that. Luckily all the firmware versions are available 
online and so far the downgrade has always worked (fingers crossed...). 
A pain.

-- Fernando

PS: I created and maintain a 56.8 3D diffusion system (in our small 
concert hall, the Stage) that has now 8 (yes, eight) Motu cards 
connected together through AVB. You can imagine it is not necessarily 
fun to deal with firmware stuff like this.

I hate products that you can buy and never know if they will keep 
working as initially advertised when you "upgrade", sigh

More information about the Linux-audio-user mailing list