Halo lore has become so much larger than just the games. Even after just the first entry, Halo: Combat Evolved, the universe was expanded into multiple books, comics, and other media that expanded ...

After you destroy the silos and sabotage the first repair center, the second repair center will open up along the northern wall of the fort. Head inside the small, newly-opened building and turn left ...

This audio log can be found in the Horn of Abolition control room, accessible after you lift the lockdown. You'll see it in the northernmost room that serves mostly as an armory.