One useful tool in the arsenal of a forensic investigator are tapes of telephone conversations and other recordings. These analyses can help determine the identity of the caller and, from background noises, can provide clues as to the location of the call.
Tape analysis of a voice can produce what is known as a voiceprint. Like a fingerprint, a voiceprint can be a unique identifier. A voiceprint relies on anatomical features of the speaker. The dimensions of the vocal cavities including the throat, nose, and mouth, and the length and diameter of the vocal cords are influential acoustic factors in producing a voice whose characteristics are unique to the individual. The chance that more than one person will display the exact voice pattern is very remote.
As well, the interplay of the lips, teeth, tongue, soft palate, and jaw muscles produces intelligible speech, and can also introduce aspects of speech such as a lisp that can help in identification . Analysis of the timing and the pitch of the voice can also unearth distinctive intonations.
Tapes can be analyzed to produce a spectrographic pattern of the speech. The aforementioned aspects contribute to this pattern. Attempts to deliberately disguise speech such as whispering, raising or lowering the pitch of the voice, and speaking with an accent, are easily recognized. A suspect may be asked to read a sentence or words in a voice similar to the deliberately altered voice, so as to produce a comparable voice pattern of the two messages. Even the electronic alteration of a voice can be dealt with, since the natural wave form pattern will still be discernable spectrographically, even if the voice is unintelligible to the ear.
Tape analysis is a commonly used facet of law enforcement investigations. Some cases are more famous than others, however. For example, tape analysis of speeches purported to be from the Saudi-born terrorist Osama bin Laden have been carried out to help determine the authenticity of the speaker. Analysis compared the computer-generated wave patterns of the taped voice with other tapes known to be the voice of bin Laden. In particular, common words such as "America" are compared from the different tapes to see if the voice wave patterns are similar or distinct from each other.
While the quality of the recording tape and the acoustics of the room the recording was made in can detract from the analysis, tape analyses of various recordings purported to be from bin Laden as recently as 2004 have concluded that he is the speaker.
see also Linguistics, forensic stylistics; Telephone recording system; Voice alteration, electronic; Voice analysis.