[Jack-Devel] AVB Backend and MIDI question

Ethan Funk ethan at redmountainradio.com
Thu Jun 20 17:48:34 CEST 2019

Very good on the AVB clocking.  I can't get the IEEE pubs legally,
since I have not been an IEEE member, or employed by a company large
enough to be an IEEE member,  since the 1990's.

As a side question regarding Jack2 and midi: I would like to use jack's
midi mechanism to pass control information between components in my
automation system.  So far I have been able to twist existing midi
packets suck as time-code, and such to control player components and
keep my mixer appraised as to source play positions and such.  However,
I have no easy way to pass meta data, such as song tags, through midi,
with out the complexity of using sysex messages and base64 encoding the
8 bit meta-data fto be passed as midi data.  Can I ignore midi's
underlying byte format and just pass 8 bit buffers to jack and expect
jack to deliver the buffers with out jack inspecting the buffers for
validity according to midi?  I only intend to use the midi ports within
my applications various player and encoder components.  I do not expect
any of this data to actually be send to a device or program that is
expecting real midi data.


On Wed, 2019-06-19 at 15:31 -0500, Chris Caudle wrote:
> On Wed, June 19, 2019 3:12 pm, Ethan Funk wrote:
> > I was under the impression...that the AVB's
> > precision network time management allows all devices to share a sample
> > clock.
> That is correct for AVB as well as for the other RTP/IP (layer 3) based
> transports such as Dante, Livewire, Ravenna, etc.
> > No asynchronous re-sampling would be required
> Correct
> > I am not clear how one goes about setting up which
> > device on the network is the clock master
> If you have access to IEEE specs see IEEE 1588-2008 and IEEE 802.1AS.
> 802.1AS is a profile of 1588-2008, there is what is known as "best master
> clock algorithm" to select the best clock.  If multiple devices are
> advertising equivalent quality ranking there is a tie breaker, I think
> based on MAC address, but don't  quote that, I am going from memory and
> have not looked at the details in quite a while.
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