Audio logs are one of the collectibles you can find throughout the Halo Infinite campaign. There are three different types of audio logs you can find; UNSC, Banished, and Spartan. There is one audio log that can be found in the Outpost Tremonius mission. Here is where you can find it.
Outpost Tremonius is the third mission you will undertake in the Halo Infinite campaign. This mission starts after you defeat Tremonius and ascend to the surface of the Halo ring. Once you get off the elevator, progress through the mission until you open the door to the outside. Immediately after opening the door, enemies will fly in and the area will soon become a battlefield.
Take out the enemies before searching for the audio log. This will make everything easier. From where you are first exposed to the outside elements, follow the path forward and go under the large overhanging structure. Before getting underneath it, you should notice some weapons and containers to the right against the cliff. The audio log can be found leaning up against the containers.