Voice Biometry and its use in Digital Forensics

Sound is a vibration that propagates as an audible wave of pressure through air.

The sound has a source that is often a vibrating solid object. When the frequency and time evolvement of the wave are observed, the source may often be identified. It may have unique spectral or temporal characteristics. 

In the case of humans, we speak about the human voice. The sound is produced when the air goes from the lungs through the glottis. Then it is further modulated, the wave is reflected, attenuated, and new frequencies are created, when the air goes through the human vocal tract. It means through the larynx, oral cavity, transformed by the tongue, gums, teeth, and lips.  Each person has a different shape and configuration of these organs. For example, women or children have a smaller body, shorter larynx, and, therefore, their voice has a higher fundamental frequency. The anatomy may vary with the human race (place of living) too, for example, American vs. Asian people. Then people move their vocal organs during speech. These movements are also unique. Some of them are learnt during childhood (dialect, the pronunciation of some words, pronunciation defects), and some of them may not be changed. Therefore, current voice biometry techniques investigate both the frequency representation of speech and its temporal evolvement.

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