What is "undubbing"

Undubbing is a type of video game hacking, which involves modifying the contents of an officially localized video game to match the audio and voice acting to its country of origin while retaining the translated text of the country in which it has been localized.

A typical candidate for an undub is a Japanese game which has been published in the U.S. with text translated, and voice acting re-dubbed in English by the localizing publisher, but without an in-game option to change the audio back to its original language due to lack of space on the media, licensing restrictions, marketing reasons or other publishing or development concerns. The process of undubbing consists of reverse-engineering the contents of both the localized and the original versions of the game, locating the audio resources within a ROM or an optical media image in the localized game, and replacing them with the audio data from the original version.