Don’t overcomplicate
… Just drag your audio file from the file manager and Ctrl+Drop it into your note!
You’ll get a perfectly encoded file:// link like this:
[AC_DC - Hells Bells](file:///home/matthias/Musik/Tagged/AC_DC/AC_DC%20-%20Family%20Jewels/AC_DC%20-%20Hells%20Bells.mp3)
Upon clicking the link, the system-defined audio player will play it.
Only drawback: This type of link cannot be embedded (using a ! upfront) to get the Obsidian audio player. That only works for files in the vault.
If it’s a folder with many audio files (not too many or Obsidian will lose speed!), @Geffrey’s idea of symlinking might be better.