Forensic Speaker Identification & Speaker Profiling by Employing Forensic Phonetics, Aural-Acoustic Method & Identifying Abnormal & Pathological Speech

by Namrita Raje
(Noida, U.P., India)

The voice is the very emblem of the speaker, indelibly woven into the fabric of speech. In this sense each of our utterances of spoken language carries not only its own message, but through accent, tone of voice & habitual voice quality.


It is at the same time an audible declaration of our membership of particular social/ regional groups, of our individual physical & psychological identity & of our momentary mood. Laver (1994 : 2)

It was not before 1941 that the advent of Speech Spectrograph took place in Bell Laboratory, US, Dr. Ralph Poter used this technique for military purpose in World War II. Later in 60’s Lawrence Kersta & in 70’s Oscar Tosi were the pioneers of Speaker Identification.

The Forensic Speaker Identification (FSI) and Speaker Profiling ( done in absence of any suspects) is invincibly required to solves cases such as kidnapping, blackmailing, hoax, threatening calls and false alarms too the evidence is in the form of Telephonic conversations, tape recording, digital recordings of speeches. Speech Transcription is required to make written transcript of speech content required in Sting operation cases and incriminating conversations.

1.Forensic Phonetics: is a part of FSI and Speaker profiling. Its an application of the subject of phonetics. When Forensic phoneticians compare & describe voices, they generally do so with respect to linguistic units, especially speech sounds like vowels and consonants, They might observe for example that the ‘ee’ vowel in two sample are different; or the ‘th’ sound is idiosyncratically produced in both. It is therefore necessary to understand something of the structure of speech sounds, how they are used described & how speech sounds are produced i.e. Articulatory Phonetics.

2.Aural and Acoustic Method: The recordings after being properly stored are amplified and heard/aurally examined first for what needs to be compared from the point of view of their linguistic and non linguistic features to determine:-

Voice Quality: Tone, Pitch, Intensity, Frequency, Volume, Rate of Speech (ROS), Abnormalities.

Speech Quality: Pronunciation, Accent, Speech sounds like vowels and consonants, plosives, fricatives, nasal and throat sounds and coupling effect, Grammar, Stress, Syllable stress, Intonation, Rhythm, Fluency, pacing, Phrasing and Blending.

Speech Content: Liaisonse & Glides, Word usage contrast. It is generally assumed that similarities & differences between forensic speech samples should be quantified acoustically & acoustic comparison is an indispensable part of Forensic Phonetic investigation.

Spectrographic Method: The frequency is recorded against time the length of each striation signifies intensity, fast fourier theorem is used for signal processing and reading graphs and Bayesian rule of probability to quantize the result further statistics to properly reach a conclusion.

3.Identifying Pathological Speech and Abnormalities: On November 12, the independent Arabic station al Jazeera broadcast a recording of a call it claimed to have received from bin Laden, in which the al Qaeda leader praised recent terrorist attacks and promised more of the same. The CIA and National Security Agency immediately turned to their voice analysts.

Tom Owen the famous scientist was called upon in this matter. And every one wondered what he would do with a short, poor-quality recording? The biggest hurdle in FSI besides cold, cough, momentary mood i.e. intra-speaker variations respectively.

Examining a spectrogram is only half of his job. His is the art of listening for the multitude of quirky mannerisms and pronunciation foibles peculiar to each voice. A trained ear can detect the subtle whistle caused by a missing tooth, a person's tendency to swallow in the middle of a sentence, even the way someone sets his or her jaw when speaking. Apart from that speech defect arising out of proper functioning or co-ordination between resonators and articulators along with neurological faculties responsible for speech production, Asthma and use of repeater words or phrase; Takiya Kalaam when identified and tried to prove acoustically proves significant evidence in personal identification.

Thus the multi disciplinary basis of FSI comprises at least Phonetics, Anatomy, Physiology, acoustics & psycholinguistics, cognitive psychology.

Keywords:

Forensic Speaker Identification, Speaker Recognition, Speaker Profiling, Speech Transcription,Inter-Speaker and Intra-Speaker Variations, Bayesian rule of probability, Forensic Phonetics, Phonemes, Phones, Allophones, Fricatives etc. Voice spectrography, Acoustics, Fast Fourier theorem, Voice Stress Analyzation, Speech production, Resonators, Articulators, Pathological Speech, Speech defects