Half-Life Episode Two begins exactly where Half-Life ended, after accepting the job agreement with Gman Gordon freeman is sent back to the Black Mesa Research Facility, why? Its up to you to find out.
The Amnesia sound engine is a implementation of the FMOD Ex library into Half-Life as a complete replacement for the original audio engine. Developed by Rohac Richard this sound engine is what this game makes use of.
The sound engine is compatible and integrated with any of the original Half-Life audio systems, sentences, mouth movements, materials, entities and DSP effects are all supported natively.
Inside the archive there is the source files required for a HLSDK integration, but there is not a implementation tutorial, it was lost long ago so installation must be carried out by a skilled HLSDK programmer.