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
Alteration and modification of recordings: A woman believes she is being sexually harassed. She hides a recorder in her clothing or in her purse. The recording she makes is likely to have a great deal of noise and may contain various stops and starts as well as clicks. The issue then arises as to whether the recording is a true and veridical representation of the conversation that took place or whether it has been altered. The recorder may have been set on voice activation, which causes it to start or stop depending on the loudness of the ambient sounds. The recording may have been in the possession of several people, some of whom may not have known how to operate recorders properly and who could therefore have erased parts of the recording inadvertently. Or parts of the recording may have been deliberately erased because they contained material that would have been embarrassing to the person making the recording or even exculpatory for the other party.
Waveform graphs: An expert can examine waveform graphs that show detailed information about the clicks and other noises on the recording. Such graphs can distinguish between environmental sounds, such as could be caused by bumping the microphone, as opposed to the clicks made by exercising various switch functions on the recorder. If it is possible to gain access to the recorder on which the recording was (alleged to have been) made, it is generally possible to duplicate the clicks made by exercising the functions of the recorder and show whether they were or were not made as claimed. The resulting waveform graphs can be displayed to the jury.
Magnetic development: Magnetic development renders the magnetic patterns on a tape visible. Start and stop signatures, erasures and other signatures can be detected this way.
Can a recording be altered in a way that is undetectable? There is no easy answer to this question. It is a game of "cat and mouse," with the advantage to whoever is the more knowledgeable. A skilled manipulator with access to a computer and common software can make simple modifications such as deleting the word "not" rather successfully. More extensive changes are correspondingly more difficult to make undetectably.