[linux-audio-user] resend: more about sync

Kai Vehmanen kai.vehmanen at wakkanet.fi
Tue Dec 16 15:16:52 EST 2003

On Tue, 16 Dec 2003, Aaron Trumm wrote:

> I've been trolling and testing various sync methods and I've noticed some
> questions popping up.  Is it just me or is the linux audio situation a bit
> incomplete at this point with regard to information on that subject?

Although a lot has happened during the last few years, syncing apps (and
devices) is still very much work in progress. Also, these issues are
really, really hard, and this slows down development (and also user 
adoption of new features).

As a little background, common transport control was identified as a key 
requirent for audio app frameworks already in 2001 when the issue of audio 
servers was heavily discussed on linux-audio-dev. From this discussion, 
JACK got its start. My LAAGA website is still pretty relevant:


... the problem statement is still very much valid, and will be until all 
the popular Linux audio apps have good JACK and JACK transport support.

> It may just be that most of the programs are still struggling to develope
> sync techniques (MTC, MMC, ADAT sync, SMPTE, jack transport, etc. etc.), but
> also is there a relative lack of info/tutorials/etc?

Yes, we need more pioneers - both users and developers who push these 
things forward.

> one basic hole I see at least in my understanding, is what the HECK is
> jack_transport, how does it fit in, etc.?  

A way to achieve "common transport control" across running audio apps. 
I.e. when you press 'play' in one app, all apps will start running. See
Jack O'Quin's excellent design document at:


At this point, JACK transport functionality (APIs and the server
implementation) is pretty much ready. Now all that we are missing are
applications that support it. Some apps already support it (Hydrogen,
JAMin, Ardour, Rezound, Rosegarden, Ecasound and few others), but level of
support varies, and with many apps, transport support is only available in
development trees. Hopefully this situation will improve in the future.
Fortunately this is something we can affect by doing more promotation for
JACK transport. ;)

> that's ONE - there are lots of
> holes for me *laugh*  another curious one is ecasound?  it's the veteren
> around here in a lot of ways - does it sync to anything?

Ecasound has full support for JACK transport. For a step-by-step guide how
to do distributed multitrack recording, see this mail from me to


In the mail I talk about need for latest CVS versions, but nowadays
Ecasound 2.3.0 (and newer) and JACK 0.90 (and newer) are sufficient.
Another, simpler, step-by-step JACK transport example is described at:


As for MIDI-support, Ecasound has basic support for sending MMC and 
MIDI-sync, but not much else.

 Audio software for Linux!

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