[linux-audio-user] Syncing Ardour + Hydrogen so Hydrogen

Jesse Chappell jesse at essej.net
Thu May 26 22:07:16 EDT 2005

On Fri, 27 May 2005, Stuart Allie wrote:

>> On Wednesday 25 May 2005 21:02, Aaron Trumm wrote:
>>>> we just need a change from a tempo of 86bpm to 94bpm and back
> again
>>>> ... how do we do this in ardour? will i have to record the
> hydrogen
>>>> tracks into ardour at the different tempos, and then adjust the
>>>> ardour tempo track to match up? that would sort of suck ... other
>>>> approaches?
> Unfortunately, Hydrogen is broken with regards to tempo changes at the
> moment. (I'm using 0.9.1 and trying to work out where the problem lies,
> but no luck so far.) There is a new beta release, 0.9.2.beta2 I think.
> It might be worth giving that a try.  I posted on the hydrogen forums
> pointing out that the behaviour was broken, and there was no response;
> but looking at other postings there, I am sure that the developers are
> aware of the problem - we can only hope they are working on it.

This isn't really Hydrogen's fault.  The problem is that JACK 
transport does not yet provide enough information to 
sample-accurately let hydrogen know exactly when the tempo change 
occurred.   If it did, H2 can use it to calculate different tempo 
starting offset for doing the BBT -> frames conversion.   As it 
stands now, H2 (and sooperlooper) always calculate the audio 
frame assuming the current tempo started at frame position 0. 
Thus only a constant tempo will ever be correct when synced to 
jack transport.

A workaround solution for apps such as H2 or SL would be to add 
another item to the jack transport position struct that 
represents the frame position that the current tempo started on. 
The timebase master would update this value along with the other 
BBT items.

The ideal solution would be to come up with some way to share a 
complex tempomap among all jack clients, but is obviously much 


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