[Jack-Devel] AES67 / SMPTE ST 2110-30

Chris Caudle chris at chriscaudle.org
Thu Sep 28 22:21:32 CEST 2017

On Wed, September 27, 2017 9:20 am, Philippe Bekaert wrote:
> Anyone working on AES67 / ST 2110-30 interfacing with jack audio?

Merging Technology is working on an ALSA virtual sound card that
interfaces to a Ravenna device.  Should work with generic AES67 devices as

The state of the driver is very strange, the source is marked GPL2 or
later, but it is stored in a git repository with password.  So I can give
you the copy of the source I have, but you have to talk to Merging to get
access to the repository.
Additionally there is a user space daemon required to configure the
driver, connect to streams, etc. that is not released.  I do not have a
copy of that yet, I am just studying the kernel mode ALSA driver at the
moment, but I do not understand the intentions of Merging Technologies
yet, I think the kernel mode driver will never be accepted upstream if
they have a closed user mode component.  Probably the kernel mode is GPL2
just to meet requirements to link with the kernel.

Also the current version of the kernel driver does not compile.  There are
a couple of obvious mistakes that I have just not had time to correct and
send back patches yet, but the fact that the mistakes are so  obvious does
not give me confidence that Merging is appying much attention to this
driver at the moment.

On Thu, September 28, 2017 6:36 am, Philippe Bekaert wrote:
> though support for some non-consumer features like PTPv2
> is needed for high timing precision.

As far as I can tell none of the existing vendors of audio hardware is
using switches with transparent clock support.  For lowest latency you
would need a network card with hardware timestamping, but some not very
expensive Intel cards have that, and software timestamping works if you
accept  higher latency.  Basically just restating what you wrote

> My impression is that AES67 is way better received by industry

Especially now that Dante has an AES67 compatible mode.  MOTU has AVB
pro-sumer style equipment, but for true professional equipment it seems
that most gear uses Dante (which now has an AES67 compatible mode in the
latest firmware versions) or Ravenna (started primarily in broadcast by
now promoted very heavily by Merging for recording use).

> I’ll start with the manual configuration.

I think Ravenna uses SIP, which should be relatively well supported with
libraries developed for telephony and chat use.  Maybe a configuration
interface that passes in the required information, and then you can have
separate front ends, one completely manual, one which queries SIP, etc.

> Some aspects of AES67 may be subject to patents (the standard specs
> document explicitly mentions audinate).

Ravenna stick to IETF specified protocols and is explicitly patent free. 
I am not sure what the Audinate patents cover, but the guys who developed
Ravenna are convinced they do not cover implementations which stick to
using just the IETF protocols plus PTPv2.

> AES67 is the greatest common factor in proprietary interfaces including
> Ravenna, Dante, a.s.o. Ravenna, Dante a.s.o have AES67 compliant profiles.

I would not call Ravenna a proprietary interface, since you can download
the description of the protocol with no license, and it explicitly just
groups together existing protocols defined by IEEE and IETF.

> You’ll be able to connect your jackaudio linux box to Ravenna, Dante etc

> equipment if you set up that equipment in AES67 compliant mode

Note that the earlier Dante design used a different clocking and discovery
scheme, only the newest revision has an AES67 compliant mode.  And AES67
is basically a subset of Ravenna, so if you have additional options for
buffer size and sample rate beyond the minimum required by AES67 it should
be pretty easy to be fully Ravenna compliant.

> My intention is to implement AES67 support as a jack client operating
> entirely in user space.

Another approach might be to use the GPL2 or later implementation of ALSA
virtual sound card and do a reverse engineered user space tool to
configure the ALSA driver.  Should be a similar amount of work but then
the driver would work for any ALSA capable software.
Now that I think about it probably would not make much difference, I can't
think of any audio production software on linux which is not jack capable.

> The alternative is the implement it as a virtual sound card driver, but
> that seems more involved.

Indeed, but that work is already done.  It just needs to be more widely

> Ideally, I should be able to adjust the audio card clock to the system
> clock or PTPv2 hardware clock on the network interface itself.

I'm not aware of any audio hardware that lets you do that.  You could
potentially have a device which locks to the PTP clock and lets you
specify the sample rate for creating a word clock or AES11 clock for
synchronizing other equipment.

> Instead, I intend to stick with sample rate conversion, to keep audio
from the
> network and in your audio card synchronised, and prevent glitches.

I would recommend the zita resampling library.  Jackd 1.x family already
incorporates that, jackd v2 family needs to use zita-a2j and zita-j2a
external clients.  Those should work unmodified to transfer between a
hardware sound card and the ALSA virtual sound card.  Maybe another reason
to re-use the Merging work.

> What I do not have at hand right now, is any other AES67 equipment.

If you have a Windows machine you can use the ALC Windows virtual sound
card if you have a supported Intel NIC with hardware timestamp support, or
you can use the Lawo Windows virtual sound card which supports software
timestamping and will work on any network card.  I tried out the demo
version of the Lawo card and was able to transfer audio from one Windows
machine to another (using an external master clock created by transferring
NTP time using linuxptp on a small linux machine).
The demo version of the Lawo software only runs for 15 minutes at a time
and has to be restarted.  The paid version costs about 200 dollars/euros.

Cymatic Audio are working on what should be a relatively affordable
Ravenna interface.  It was originally said to be available in fall of
2016, but is now almost a year and a half late because of re-design
undertaken after feedback from the first beta users.  Now said to be
available "by the end of the year."

The existing Cymatic 24 channel interface was just reduced in price
considerably, it has a Ravenna option card available.  More expensive but
available now:

This card I found on eBay is said by the developer to have been checked
out with the Lawo virtual sound card:
That device is pretty limited, it has a single connector which you have to
configure as either input or output, it cannot operate as a full duplex
Only a little over 100 euro, so much less expensive than the Cymatic
device, much less a Merging NDAC or Hapi.

> Who has AES67 equipment and would possibly be willing to assist, at least
> in testing once time is there?

I am willing to assist.  I do not yet have AES67 equipment, but I am
considering what to get.  I may start with that inexpensive Hasseb device
if it appears that the Cymatic 4 channel device will be delayed again.

Chris Caudle

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