Dr. Papcun's Report on the Rodney King trial appears in the book "Letters of the Century" (Read the letter) by Grunwald and Adler
"Your appearance as the final witness in the Rodney King trial was decisive as to the outcome."---Milton Grimes, Esq.
"Dr. Papcun is a star!"---Attorney subsequent to Dr. Papcun's deposition, following which the opposition declined to proceed
"Please send your bill in before you find out how delighted the client is." --Attorney following a directed verdict subsequent to Dr. Papcun's testimony
A series of threatening telephone calls is received at a large utility company. Some of them are recorded. On the basis of references in the telephone calls to certain facts about the company that would be known to only a limited number of people, a list of suspects is developed. To obtain exemplars of the voices of the suspects, telephone calls are placed to these suspects and are clandestinely recorded. (Note: It is important to check the legality of this procedure in a given situation and jurisdiction.)
Recording the exemplar: Perhaps the commonest error in cases like this is that the person placing the exemplar call talks on at great length, giving the suspect no time to talk. Questions that can be answered with "yes" or "no" or similarly short answers are not very useful. Planning and practice for the call are worth the effort. An expert can advise how to construct the call.
Listening: Identification should begin with listening. Are the voices known to co-workers? Do they sound like they were disguised? An expert can advise on what to listen for, such as dialectal issues or special idiosyncrasies.
Graphs: Additional information can be provided by graphs called "time-varying acoustic spectrograms", which have been called "voiceprints" in the popular media. However, the implied analogy between so-called voiceprints and fingerprints is not valid. A fingerprint is an image that results from your physiology, whereas a so-called voiceprint is a record of the consequences of your actions in speaking (as well as the physiology of your vocal tract). Time-varying acoustic spectrograms are graphical pictures of sound. Time runs along the bottom axis. The vertical axis is frequency, with lower frequencies at the bottom and higher frequencies at the top. Intensity is represented on a color scale, generally with low intensities shown in blue and higher intensities shown in red. "Voiceprints" as an aid to understanding: Time-varying acoustic spectrograms can help localize interfering sounds and provide an objective basis for eliminating them. They can provide a graphical basis for assessing various idiosyncrasies of the speaker's voice. As a graphical method, they provide a way to portray features of the voice, which would otherwise be fleeting and evanescent. Ultimately however, they are only an aid to understanding the issues, and the ultimate judgment rests on human interpretation.