Audacity is a free, open-source, audio editor. It can be downloaded from the Audacity website.
Audacity can be used to create the flashback voice effect from the original Amnesia game. This effect can be achieved with the following steps:
Audacity comes with support for exporting to OGG format. OGG format is the recommended format for audio files for Amnesia. Simply import (or open) an audio file into Audacity, then click on File > Export and choose OGG Vorbis for the file type.