Voice Biometric Technologies

The use of voice for biometric verification seems natural and suitable. From an early age, we learn to distinguish the sound of our parents' voices. Voice provides a very important source of sound for the sense of hearing. The understanding of a voice we perceive can tell us a lot about someone. It can tell us their relation distance to us, their feeling, and, most prominently, we can associate the voice with someone we know. Like recognizing a face, we have all made the inaccuracy of thinking that we documented a voice when we did not. This could have happened due to the acoustic conditions under which we heard the voice. In addition, our sense of what direction and how far someone is away from us can also is fooled. To try this, have an important person stand behind you and speak to you from a given side. Then take a paper tube and hold it up to the ear that is closest to the person. Have that person speak again. Unpredictably, the person now seems to be closer on the other side. That is because the sound waves need to travel farther to reach the ear. Thus, in measuring the time it takes the sound to be heard in both ears, the brain is tricked into thinking the person is essentially closer to the other side.

This demonstrates that even the most multifaceted machine, the human brain, can be fooled by sound and, in turn, by the human voice. If it is possible for the brain to be fooled, it seems only logical that a voice biometric can be fooled as well.

General explanation of Voice Biometrics

When we speak, words can be broken down into individual components known as phonemes. Each phoneme is delivered with pitch, cadence, and inflection. These three aspects of voice give each of us our unique voice sound. Even though we are all unique individuals and speak for ourselves, we can all sound very similar. This similarity can come from cultural and regional influences in the form of an accent; also, we learn certain inflections and pitches from our family. That is, if you spend enough time around someone, you can take on some of his/her voice characteristics. Not surprisingly, we have all at one time or another thought we heard one person speak when it was another.

The voice is a physiological and behavioral biometric. That is, it is influenced by our body and the environment we are in. For example, as children grow and pass through puberty, the voice changes. As we grow older, the voice takes on other nuances. Additionally, the sound of our voice can be different if we are talking in a large opera hall or a phone booth, as both have a very unique set of acoustics that will affect the sound of our voice. Therefore, it is possible that our voice does not always sound exactly the same. This again raises the question of the use of voice as an acceptable biometric for network security.

How Is the Voice Captured?

The voice can be captured either through the use of dedicated resources or existing infrastructure. An example of a dedicated resource is a stick microphone attached to a computer. Existing infrastructure can take the form of a telephone.

The use of either type of capture device is prejudiced by two qualities. The first is the physical superiority of the device, and the second is the environment in which the sample is being taken.