Voice Prints

If investigators have a recording of voice, they can use voiceprints, just as they use fingerprints, to help identify the person on the recording. A voiceprint is a pattern of wavy lines and whorls produced by a recording of a person’s voice. Voiceprints are as unique as fingerprints. Try the following activity to simulate your voiceprint.

Materials

- glue
- ¼-by-¼ inch (6-by-6-mm) mirror
- speaker with connecting wire (a speaker and connecting wire from an old radio is easiest to use)
- cassette recorder
- wire cutters
- flashlight
- cassette recording of your voice
- adult helper

Procedure

1. Glue the mirror to the speaker, about halfway between the center and the edge of the speaker.
2. Ask your adult helper to connect the speaker to the cassette recorder. This can usually be done by using wire cutters to remove ½ inch (1 cm) of insulation from the free end of the speaker connection on the back of the cassette recorder.
3. Darken the room, and then shine the flashlight onto the mirror. Note where the light reflects off the mirror and shines on the opposite wall.
4. Turn on the cassette recorder and play the tape. What happens to the light’s reflection on the wall?

Explanation

Voiceprints can used to identify a recorded voice. In this activity, the recorded voice creates vibrations that are sent to the speaker. These vibrations are unique to the voice and to the words that are being said. The vibrations cause the speaker and the mirror attached to it to move, which causes the light reflected off the mirror to move in the same direction. If you could mark the path that reflected light traced, you would have a line that similar to a voiceprint. It would be possible to identify who, or what, made the sound.

Forensic scientists use voiceprints to compare recorded voices. They normally have a suspect record a 2 ½ -second speech that uses then ten most common words: a, and, I, is, it, on, the, to, we, and you. They then compare the voiceprint used as evidence in a crime.

Detective Science in Action
The first application of voiceprints occurred in Connecticut, where a voiceprint was used to prove the innocence of suspect. The suspect was a man accused of using a telephone to make threats to a family. The principal victim claimed that the suspect had made the calls, while the suspect protested his innocence. Investigators made tape recordings of both the phone calls and the suspect’s voice. An analysis of the phone calls revealed that they had actually been made by two individuals disguising their voices. The suspect was released and the two guilty persons were arrested.