I made a 40 min live recording, resulting in two tracks directly on Ardour and one on my Zoom.
When I import the Zoom file and sync it to the beginning of the Ardour tracks, I realize it is shorter. What is the cause of that length difference, and how can I solve it elegantly ?
So short version, out of sync clocks.
This could be a settings issue, for instance the zoom recording at 48k while Ardour recorded at 44.1k and importing them at the same sample rate. But it could also be harder to see as in actuality while a device may say 48k, it may actually be recording at 47783Hz instead for instance, while the one next to it is recording at 48134Hz. They both would report 48k in this case, but there is some variation. This is why in studio situations you have to make sure you are using a single digital clock, and have all digital devices lock to that clock.
The only real way to address it is to stretch the audio, or periodically resync (Assuming you have silences etc. you can edit to allow that. The former you will have mixed results within Ardour itself for, but could go to third party tools as well for this purpose. The latter as long as you have periods where you can make edits, you could conceivably split and manually resync, but this will depend on the material you are working with and the amount of work will depend on how far out of sync the two clocks were.
Seablade