Synchronization with Acoustic guitar track

I am working on a song with 5 imported audio tracks and I recently recorded an electric guitar track on top of those 5 imported tracks with success. I attempted to record an acoustic guitar 7th track, (using the same setup that I recorded the electric guitar on. i.e., direct in. . . not mic) and experienced my first synchronization issue. The acoustic track is slightly out of sync. Can someone put me on the right track to solve this sync issue. I read the manual but I have to admit I find it difficult. I should say that when I open the session I get the warning “2023-03-15T10:58:24 [WARNING]: AlsaAudioBackend: cannot acquire realtime permissions.” Could this have anything to do with this sync problem? Thanks for any help anyone can give me.

It might, if it causes dropouts. Check top-right in Ardour’s status-bar if there is a number in braces after the DSP load. During a dropout nothing is recorded and the recorded signal will be early.

On most GNU/Linux distros the easiest way to setup realtime permissions is to install JACK - even if you do not use JACK, the package sets up realtime permissions. Alternatively you can manually edit /etc/security/limits.d/audio.conf as described at How do I configure my linux system to allow JACK to use realtime scheduling? | JACK Audio Connection Kit and re-login.

All soundcards have a systemic latency, which delays the signal. The recorded signal will be late:

[hardware-latency] → playback → headphone → mic → recording → [hardware-latency]

In some cases it is small and negligible, but you can measure this systemic latency and let ardour compensate for it, using Ardour-Menu > Window > Audio/MIDI Setup → Advanced → Calibrate Audio Latency.