Joining audio in a video editor means importing, aligning, and exporting a project. This does the one operation: decode each file in turn and write them into a single output.
Order
The cards are the timeline. Move a file up or down with the arrows, and the number in its corner is where it lands.
Files are used whole. To join parts of files, cut them first and then merge the pieces.
Formats and rate matching
The output format is yours to pick, independent of what went in. Choose WAV or FLAC when the result is going back into an editor, MP3 or M4A when it is going out to listeners.
Rate and channel matching happens once, on the way into the encoder. Joining a mono voice memo to a stereo music bed gives a stereo output with the mono file centred, not a file that switches layout halfway through.
Blend joins
The default 5 ms fade at each seam is short enough to be inaudible and long enough to remove the click that a hard splice between two unrelated waveforms produces.
Raise it to 30 ms or more when the files come from different rooms or different sessions, so the change in noise floor arrives as a fade instead of a jump.
Podcast assembly
Intro, interview, and outro as three files, joined in one pass with a 20 ms blend. The output is one M4A at the bitrate you choose.
If the parts were recorded at different levels, level them first: joining does not change gain, so a quiet interview stays quiet next to a loud intro.
Limits
Nothing here re-times, ducks, or crossfades material over the top of a neighbour. It is a butt splice with an edge fade.
For overlapping music beds or a fade that runs across a join, an editor with a timeline is the right tool.