Audio log (Halo 3: ODST)

Audio Logs are set to be in Halo 3: ODST. Nothing is known about them, but speculation seems to be that they are logs left by ODSTs, Marines, or civilians retelling the events concerning what happened in New Mombasa.

There are four [http://halo.wikia.com/wiki/Halopedia:News/24_June_2009/Halo_3:_ODST_Achievements_Discovered! Halo 3: ODST Achievements] that require you to uncover a particular amount of Audio Logs in order to be unlocked.