Nirmala Devi voice recording: How & why it was done

By Nivedhika Krishnan Published on Jun 29, 2018 01:45 PM IST

Chennai: Quite apparently, sleuths solving the sensational case involving Assistant Professor Nirmala Devi are going by the wisdom in police circles: Eyewitness testimony is notoriously unreliable and science-backed evidences are to be relied on.

The tainted teacher was arrested recently for allegedly trying to lure a group of college girls to fulfil sexual desires of 'top officials' for academic and financial gains.

Following the leak of an audio clip, in which she was heard wooing the girls, she was suspended from the Devanga Arts College in Arupukottai and arrested.

On Thursday, Nirmala, who was brought from Madurai to Chennai, underwent a voice test at the forensic office here that lasted three hours.

The CB-CID were insistent on getting a voice test of the professor though she had accepted the charges against her, it is learnt. "Because it strengthens the case and will also avoid any confusion in future," said an officer.

On how the process is done, sources said, "Audio forensic evidences can be obtained only under the direction of the court in our country. And the court will grant permission only if it is convinced that voice test is required for an official inquiry and will help the case to move forward to the next level of probe."

Elaborating, they said, "The primary aspects of audio forensics are establishing the authenticity of audio evidence, performing enhancement of audio recordings to improve speech intelligibility and the audibility of low-level sounds, and interpreting and documenting sonic evidence, such as identifying talkers, transcribing dialogue, and reconstructing crime or accident scenes and timelines."

The voice recognition dates back to 40 years ago and uses the acoustic features of speech that have been found to differ between individuals. These patterns reflect both anatomy that deals with size and shape of the throat and mouth and learned behavioural patterns, namely voice pitch, speaking style.

"The audio forensics involve acquisition, analysis and evaluation of sound recordings that may ultimately be presented as admissible evidence in a court of law," he said.

Forensic scientists reconstruct a crime scene with available pieces of information to form a full picture of what happened at a crime scene. This information is then used by the police and prosecutors to bring a criminal to justice, explained a senior official.


In the case of Nirmala Devi, she was given a text, a verbatim of her WhatsApp recording, and was made to read it aloud during the test. It was recorded and will be analysed on the basis of voice pitch. The Forensic Department will submit the findings in a sealed cover to the court. It is expected to play a major role in the case.