Forensic Phonetics

Forensic linguistics is a field of applied linguistics involving the relationship between language, the law, and crime.

Area of phonetics that deals with questions in which speaker identification is relevant to solving a crime.

Prominent cases:
• hoax calls to emergency numbers
• sexual herrasment calls
• bank robberies in which robbers are masked but recorded
• telefone calls from kidnappers
• crimes (e.g. rapes) in darkness in which victim cannot see but hear the perpetrator

Links of Forensic Phonetics:
http://www-users.york.ac.uk/~pf11/Links%20for%20Forensic%20Phonetics.htm

In a New Article in the Economist

Volker Dellwo, a phonetic scientist from University College London, conducted a small study in which he asked an actor to read 25 sentences in either his natural voice or with an accent. Dr Dellwo found that the actor’s fundamental frequency went from 120 hertz to 170 hertz when disguised. Furthermore, phonetic experts found it difficult to say in many cases if the same person was reading the sentence.

Dr Dellwo thinks it would be better to focus on rhythmic aspects of speech, such as the way a person lingers over vowels. He has found that the percentage of speech that is vocalic, as opposed to consonantal, is not only highly idiosyncratic and stable regardless how fast a person is speaking, but also is not perceived by the ear, making it hard to disguise. In the same study he found that this aspect of the actor’s speech did not change much, whether he read in a normal or disguised voice.

This study needs to be replicated with many more subjects and types of speech, but the results hint that speech rhythm could be profitably tapped by voice analysts. One snag is that, at present, the visual representation of the voice has to be tediously annotated manually for its vowel and consonant content.

However, a slightly different approach, measuring the proportion of speech time during which the vocal cords vibrate, could be automated—since software for extracting that feature already exists. If this proves viable it could become useful in police work, prosecutions and courtrooms. Scientists may yet have the last laugh.