The filename Skyrim - Voices-en0.bsa tells us exactly what is inside if we deconstruct it:
If you install a mod that replaces existing dialogue (like a voice acting overhaul mod), the mod will usually place loose audio files into the Skyrim/Data/Sound/Voice folder.
By default, the Creation Engine prioritizes "loose files" over archived files. So, if you have a modded line of dialogue in a folder, the game will play that instead of pulling the file from Voices-en0.bsa. This is how modders fix bad voice acting or change character personalities without touching the core game files. Skyrim - Voices-en0.bsa
Before we get to the voices, let’s talk about the container.
BSA stands for Bethesda Softworks Archive. It is a proprietary file format used by Bethesda Game Studios for their Gamebryo and Creation Engine games (think Morrowind, Oblivion, Skyrim, and Fallout). The filename Skyrim - Voices-en0
In the early days of PC gaming, game assets were often just loose files tossed into folders. But as games got bigger, developers needed a way to organize thousands of textures, models, and sounds without creating a chaotic mess on your hard drive.
The .bsa file acts like a .zip or .rar file. It bundles a massive number of internal files into a single, compressed package. This makes file management easier and helps the game engine load assets faster. This is how modders fix bad voice acting
The English voice set is usually split across multiple archives: