One important field in which speaker recognition is usually involved is the field of forensic applications. This concerns cases for which victims or witnesses have an auditory memory of the criminal voice and cases for which recordings are available. In the case of recordings, the content of the tapes may be important (Who is speaking? What is being said? Which sounds could be identified? ...). The tapes should usually be analysed to check whether or not they have been manipulated, erased, recorded over, etc. The signal may require enhancement to be comprehensible. In some cases, the voice of a suspect should be compared with a recorded voice. This is a very special case of speaker verification with many specific difficulties:
Various methodologies for approaching this problem have been proposed; they may substantially be classified into the following three categories according to the criterion adopted for the analysis and the characterisation of the voice signal: the listener method, the spectrographic method and the semi-automatic method.