Thanks all, that’s all useful info. I’ve convinced myself too that it’s not Jack, by adding a host of random busses, sends, and inserts and routing audio randomly all over the place. I couldn’t get it to fail.
I think thorgal’s explanation is the most likely since it seems to always occur with certain LADSPA plugins. I went back to my old known good stable installation with Ardour 2.7 on a rock-solid kernel and tried some of the same plugins there. The problem still occurred, even on a completely empty Ardour project.
Of course this doesn’t explain what was going on with jconv or the linuxdsp stuff since that’s not LADSPA. But I suppose it could still be some combination of plugins causing some wierd edge conditions. I’ve built everything from source so I may try messing with compiler options in the misbehaving plugins and see if I can improve things. I note that none of the plugins giving me problems (and all of the ones that seem to work properly) are LV2.
One question - what are denormals, and which of the settings for denormal handling should I try?
I’ve tried fiddling with the compiler options for the CMT plugins based on what the TAP plugins use. No luck yet. I notice that when using Freeverb and seeing this problem where the audio cuts out, Ardour is showing the DSP load at 90%. It really does point to something going very wrong in a plugin somewhere.
DrG Ardour has denormal protection you can make sure is enabled in its options menu.
Denormals are an issue that came up on AMD processors IIC where if a plugin was processing silence it would take up 100% of the CPU. This does not really sound like your problem.(Except possibly a denormal problem showing up after the fact on Freeverb above)
As you noted the issue with Thorgal’s explanation is that not everything this is happening with is a plugin, LADSPA or otherwise. Several of them are external Jack programs and this doesn’t explain why it is happening to them.
You mentioned rolling back to 2.7, did you try 2.8(Or was that what you were on originally) as mentioned by an above poster?
Also where are you getting your packages from out of curiosity? Some distros have known packaging problems, that shouldn’t really cause this but they show up in very odd ways sometimes.
DrG, I don’t think LADSPA is ‘fundamentally screwed’, there’s nothing really wrong with the LADSPA architecture (for what it was intended for), except the lack of a good GUI (but that’s a whole load of complication I won’t go into here…) the LADSPA specification just provides some function prototypes. To process audio you just write a function that processes a block of audio data, LADSPA just defines a method for the host to tell the plugin where the data is and how many samples there are. After that, its up to the plugin developer to do the right thing with the audio. I’ll agree that some of the LADSPA plugins do some odd things though.
It made my head hurt though.