This paper is a literature review on the subject of audio processing and intelligibility. It looks at the problem of extracting speech from noise and reviews the success of such techniques in improvng intelligibility in a number of fields of research. The literature available indicates that there is little if any chance of audio processing improving intellibility of speech noise, and a real danger of degrading it. Whilst audio processing can be used to create cosmetic improvements in a speech signal it cannot be used to improve the ability of an audience to follow the words. Audio Processing cannot be used to create a viable "clean audio" version for a television audience and any use of noise reduction behind speech in production will have simiiar problems.