UNIT 1: Introduction to Speaker Comparison

In order to be able to do a speaker comparison, audio recordings of the perpetrator and the suspect are available. Forensic language experts carry out a meticulous evaluation of two recordings to answer the question of whether the suspect is the perpetrator of the crime.

Because speaker comparison is about an analytic approach – phonetic analysis and speaker-specific characteristics, we need a more detailed analysis than the speaker profile. And nowadays this can only be created using software or artificial intelligence. We will therefore turn to the phonetic software Praat, which is well known in research and will help us to forensically analyze specific characteristics of the two voices, who are suspicious ! Let's track them down…

In this lesson, we will focus primarily on phonetic features and during the first activity, we will look at  fundamental frequency. In adult men, the average fundamental frequency is usually between 85 and 180 Hertz (Hz). In adult women, on the other hand, the average fundamental frequency is typically between 165 and 255 Hz. 

​​​​

In order to see how this fundamental frequency is measured, you will need to download a copy of Praat onto your computer. You can download it here: https://www.fon.hum.uva.nl/praat/

Activity 1: The Mystery of the Stolen Lindt Recipes

Remember from the last lesson:

We had the case of the theft of valuable recipes in the Lindt chocolate factory. We've decided that the math expert is a highly dangerous person, so we've already created a speaker profile of him. But the thing is, besides this person, we have an anonymous source who told us that he saw a person hanging around the Lindt chocolate factory late at night while the robbery was going on. Why was this person hanging around? We interviewed him and he seems suspicious, so we made him repeat the same sentence from the audio recording, to know if we're dealing with the math expert.

​

Therefore, we need to compare his voice with that of the recording we have of the robber. You will need to save the two different audio recordings on your desktop and upload them to Praat. Listen carefully and determine the average fundamental frequency of the two recordings. Is it the same person? 

UNIT 2: Analyzing Phonetic Characteristics

As we have seen in part 1 of this lesson, it can be extremely difficult to try to discern speakers by ear and guess which voice belongs to whom. Now that we've taken a look at Praat and how we can use it, we are going to dive deeper into analyzing phonetic characteristics between speakers. 

Some of the more noticeable differences that we can measure using Praat are loudness, formants, and the pronunciation of vowels and consonants (which are shown in a spectrogram). These elements can convey information about the speaker's identity or emotional state.