Exporting freezes halfway through

Exporting the session freezes, leaving DSP at 100% CPU and nothing really happening.

Setup: Intel 865 / P4 3.0 GHz based PC (1 gig RAM) with RME HDSP 9652, CentOS 5 with Planet CCRMA (haven’t updated anything in a while, so jackd 0.116.1 and Ardour 2.7.1), audio I/O via three Behringer ADA8000 8 channel AD/DAs (irrelevant in context, though)

Scenario: 90 minutes of 24 track live recording, one pass into Ardour, no additional material. Very few plugins in use (a few Mono Amplifiers, one Hard Limiter, one Stereo Reverb, nothing to overload the poor old computer).

Problem: Exporting the session freezes at about 48 minutes. Symptoms include first the computer taking ages to load more data to display the next page of waveforms, followed by jackd peaking at 9999% CPU (seriously, that’s what “top” reported even though it’s ludicrous), followed by nothing happening any more and the DSP CPU staying 100% occupied even though nothing going on, Ardour becoming nonresponsive to clicks in the GUI (“Cancel” in the Export dialogue does nothing, for example, but a “kill” does make the process go away nicely). On occasion, the qjackctl GUI becomes unresponsive too, on other occasions it stays live and can be used to stop and restart JACK, which seems to be necessary to get Ardour functioning again (just killing Ardour and restarting it leaves it unusable because the DSP is unresponsive).

Adjusting latency does not seem to change things - it only makes the freeze take place a very short while later.

(On another note, I noticed that I was unable, to begin with, to record 24 tracks direct with the RME in the lowest-latency mode. It started recording and pretty much immediately disconnected Ardour from JACK. I needed to change from 64 frames to 1024 frames to be able to make the recording at all.)

Have notice too that “view all session” and “don’t follow head” options makes export work better, if it can help ?

Changing Zoom level from whatever is the default to “Zoom to Session” seems to have allowed me to get a little further. Maybe even to the end of the session? Will see in 15 or so…

Most surprising.