Re: sample files (links)... Re: [Rosegarden-devel] jack causing the softsynth problem somehow...

[Chris C. <ca...@al...>]

On Wednesday 02 Jun 2004 1:20 am, Silvan wrote:
> 4096 48000 2 16-bit only
>
> 171 ms is the best I can do without getting a pile of xruns.

This may be the core of your problems.

Depending on the design of the soft synth, that (truly dreadful) 171ms 
of yours might be the effective resolution of MIDI event delivery 
when it's running with JACK.  A soft synth running as a JACK client 
fundamentally works to a resolution of the size of the JACK process 
block.  There are various interesting options for how it can deal 
with incoming events so that they appear to be processed at the right 
time relative to one another, but the naive way to do it is just to 
batch up all events that arrive during processing or in the gap 
between blocks and schedule them together at the start of the 
following block.  This gives the lowest average latency, but a 
relatively high "jitter" (timing inaccuracy between subsequent 
events).  I don't know what Hydrogen does, but if it works that way 
then you'd be getting up to 171ms of jitter, which is a hell of a lot 
and is pretty much what your recording sounds like.

(Actually it might only be half of that 171ms.  Your settings have a 
4096-frame block size with two blocks per hardware buffer; that makes 
8192 frames at 48KHz, which is about 171ms, but I think each JACK 
client still only deals with the 4096 frame block at a time, or more 
like 85ms.  Enough, though, I think.)


Chris