[Jack-Devel] AVB

Jörn Nettingsmeier nettings at stackingdwarves.net
Sun Feb 24 13:00:51 CET 2019

[sorry for the late reply to this one, I missed it the first time...]

On 12/31/18 1:04 AM, Fernando Lopez-Lezcano wrote:
> Yup, that is exactly why I was able to use Motu in my latest systems in 
> the fashion you suggest (out small Stage concert hall now has a 56.8 
> system, and our 3D 22.4 Listening Room has new speakers and Motu based 
> control system).
> Class compliance vs linux comes with some caveats (at least in my 
> experience)...
> If you need more than 24 channels (I use the 64 channel mode) you need 
> to downgrade your card to firmware 1.2.8+ (this is true for the 16A, 
> 24Ao/Ai and 8M, AFAIK). 1.2.9 onwards does away with that mode so you 
> are restricted to 24 channels max in class compliant mode (which may not 
> be a problem for most users).

Thanks for that hint. I'm about to get a MOTU for myself, so that's 
gonna be useful.

> Even then I found problems with the latest firmware version, input 
> channels would shift in blocks of 8 every few seconds (ie: input coming 
> in through channel 1 would suddenly appear in 9, and so on and so 
> forth). Again, downgrading a bit gets rid of that problem.

Owwww. That sounds _very_ bad. I'm currently experiencing a similar 
problem on a Raspberry Pi when trying to cram 8 channels through a 
stereo I²S line, but I wouldn't have expected such things to come up in 
professional equipment. Well, as long as there is a known-good firmware 

> So, not so nice. Firmware giveth, firmare taketh away (with no warning)...
> The story does not end there, there are conditions in which changing 
> load in the Linux computer has effects in the AVB domain, specially if 
> the Linux computer is pretty loaded (either a glitch, or the interface 
> starts making some low level buzzes or distortion every second, or so, 
> sometimes temporarily, sometimes it gets stuck in that mode). My latest 
> thinking is that the internal processor of the Motu interface must be 
> close to being fully used, so when there is some glitch in the timing of 
> the USB packets it affects the rest of the internal processing, 
> including AVB transport. Just doing some tests a couple of days ago, 
> seems to also depend on number of AVB streams being used. But this is 
> just speculation on my part, no facts (facts are overrated these days, 
> argh).

Long as it feels truthy :-D

Do you know whether the different AVB MOTU boxes are all the same in the 
way they handle AVB (as in, identical subsystem/firmware/drivers)? I'm 
eyeing the one with eight mic preamps (MOTU 8 Pre-es)...

> Yes definitely very very nice.
> You can even control most of the internals through http+JSON or OSC and 
> we do that to control the internal routing matrix and modes in our systems.

That's very good to know. Does it have a sane documented interface, or 
are you basically reverse-engineering the mixer website?

>> Christoph, would you agree, or can people who do not frequent the same 
>> circles of hell as you are so competently doing consider "native" AVB 
>> yet? I've been lurking, but mostly been very, very afraid :)
> I'm forever wanting to do the full AVB stack, never find the time. The 
> is now even a branch in the OpenAVnu project that apparently can use a 
> non-AVB ethernet interface. I did some tests a while back and managed to 
> get Linux to sync to an AVB Motu card, and the card would switch into 
> "AVB mode". Never went further than that.

I've been lurking on the open-AVB list for a long time, nothing much 
happened. Then I talked to an AVB guy with Meyer Sound at the last 
Tonmeistertagung, they just renamed everything "Milan" and are seriously 
getting off their asses now (probably panicking about the Dante camp 
just having announced basic video capability). Loads of new products, 
finally talk about cross-vendor interoperability and interesting 
plugfests (they showed Meyer AVB gear talking to Shure wireless units 
and some professional power amps by another brand). Let's hope some 
crumbs fall into the land of free software.

All best,


Jörn Nettingsmeier
Tuinbouwstraat 180, 1097 ZB Amsterdam, Nederland
Tel. +49 177 7937487

Meister für Veranstaltungstechnik (Bühne/Studio), Tonmeister VDT

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