Just downloaded Elan 5.9. I have a sign language video for which I would like to add voiced interpretation. Is it possible to record audio directly in Elan? If not, how do I add an audio file into an Elan tier?
No this is not possible in ELAN. Currently there are no recording facilities in ELAN (this is on the wish list) and the content of tiers is always text. It is possible to add additional audio files (via Edit->Linked Files) but these are supposed to be synced to the (more or less) entire timeline of the video. In other words, you would have to have all the voiced interpretation(s) in one audio file.
Also on the wish list is support for linking files (audio, video, text etc.) to individual annotations (which, I suppose, is what you actually want). Although some preparatory work has been done to support that, this is not yet possible.