[ardour-dev] MTC sync

Per Sigmond per at sigmond.no
Thu Mar 10 13:27:29 PST 2005


This is my first post to the list, let me first say thank you for a very very 
promising program! Can't wait to see the remaining bugs to get ironed out :-) 
Hope I can be to some help.

These days I am trying to make ardour sync up with two devices; a Korg D12 
harddisk recorder and a windows pc running "The JAZZ midi sequencer". There 
are some issues I'd like to ask about:

* Sloppy quarter frame timing?
When ardour is master, the timing of MTC quarter frames coming from ardour 
seems very sloppy (the D12 manages to sync to it after a while, but JAZZ 
plays very staccato). I guess this is linux kernel timing problems? Any cure 
apart from serious kernel hacking?

* The "two frames off" effect?
The "sloppy timing" problem led me to rework the JAZZ mtc slaving code (after 
years of not touching the program, yes I am one of the original authors). Now 
it runs smoothly even with ardour :-). Working with this made me aware of 
another potential issue; the "2 frame timing offset" problem. The original 
JAZZ code did not take into account that MTC time actually arrives 2 frames 
late (8 quarter frames), which means that you have to add 2 * 1000 / 30 =~ 66 
milliseconds to the time. This is rather audible when not taken into account, 
and now JAZZ syncs *perfectly* with my Korg D12. Now to the point: is ardour 
having the same problem? (To me is seems that ardour is about the same time 
off on the clicks as JAZZ used to be when syncing with my Korg.)

* Is SMPTE offset working?
I tried to change this setting in ardour both as master and slave to try to 
adjust the offset I was hearing between the clicks, but no appearent effect. 
Is SMPTE offset supposed to be working?

Best regards,
Per Sigmond
Gjert Sorensensvei 5
4879 Grimstad
per at sigmond.no

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