Voiceprints are called pictures in linguistics. It is a vocal image drawn by a spectrograph, that is, a spectrogram of sound. Whether the analysis materials and conclusions of voiceprint can be used as evidence mainly depends on two factors.

First of all, voiceprints are unique. Second, the voiceprint is stable. This aspect is very similar to our most familiar fingerprints. The reason why fingerprints become important evidence in criminal proceedings is mainly because of their uniqueness and stability. If voiceprints are as unique and stable as fingerprints, they can be used as conviction evidence in criminal cases.

First of all, the uniqueness of voiceprint, human voice is emitted by vocal organs, including mouth, nose, pharynx and other vocal organs. The subtle differences of these organs will lead to different voices for everyone.

In addition, people will have differences in the speed of vocalization. These elements are reflected in scientific instruments, and different sound waves appear. The instruments convert the sound waves into spectrograms and show them in front of us, which becomes voiceprints. Therefore, the pattern is unique.

Stability of voiceprint: According to the expert's comprehensive investigation conclusion, voiceprint has more than 80 characteristics. Even if people deliberately change their speech speed and intonation in the case of crime, they can't change some original features of voiceprints. Therefore, through the analysis of scientific instruments, everyone's voice is stable.

The so-called voiceprint is the sound spectrum with speech information displayed by electro-acoustic instruments. Modern scientific research shows that voiceprints are not only specific but also relatively stable. After adulthood, people's voices can remain relatively stable for a long time.

Experiments show that no matter whether the speaker intends to imitate the voice and tone of others or whispers, even if the imitation is vivid, the voiceprint is always different. Based on these two characteristics of voiceprint, investigators can compare the voiceprints of criminals and suspects through voiceprint recognition technology, quickly identify criminals and provide reliable evidence for investigation and solving cases.

Because human vocal organs are actually different in size, shape and function. The vocal control organs include vocal cords, soft jaws, tongue, teeth, lips and so on. The vocal organs include pharyngeal cavity, oral cavity and nasal cavity. The subtle differences of these organs will lead to the changes of human voice airflow, resulting in differences in sound quality and timbre.

In addition, people's vocal habits are also fast and slow, and the strength is large and small, which also causes the difference in sound intensity and sound length. Pitch, sound intensity, sound length and timbre are called "four elements" in linguistics, and these elements can be decomposed into more than 90 features.

These features show different wavelengths, frequencies, intensities and rhythms of different sounds. The spectrograph can convert the change of sound waves into the change of intensity, wavelength, frequency and rhythm of electrical signals, and the instrument draws the changes of these electrical signals into a spectrogram, which becomes a voiceprint.