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Forensic Acoustics
of acoustical events, and educate the attorneys, defendants, judges, and juries about the meaning, significance, and limi- tations of the recorded evidence (Audio Engineering Soci- ety, 1996; Maher, 2009). Figure 2 depicts an interpretive an- notation that has been added to a time waveform to assist with an investigation.
Forensic Acoustics and the US Courts
Audio forensics traces its origins to the development of por- table recording equipment, and examples of the use of audio recordings in US courts date to the mid-1950s. Although the courts generally began to accept the unique importance of audio recordings, especially in cases involving speech ob- tained via clandestine surveillance or wiretaps, there were significant considerations regarding the Fourth Amend- ment’s protections against unreasonable searches and sei- zures and concern about the legal admissibility of a record- ing as being a bona fide representation of the sonic events actually present during the recording process.
The McKeever Case
Among the key cases in the US federal court system regard- ing the admissibility of audio forensic evidence is United States v. McKeever (1958). In the McKeever case, two de- fendants were indicted for extortion in an antiracketeering prosecution involving the International Longshoremen’s Association. After his indictment, the defendant McKeev- er had arranged to make a surreptitious tape recording of a conversation he had with an individual who later was a witness in the trial. During the trial, McKeever’s defense team sought to challenge under cross-examination the wit- ness’ testimony by playing a portion of the clandestine tape recording to refresh the witness’ recollection. The court al- lowed the tape to be played but only via headphones so that the witness could hear it but not the jury. When the defense then sought to have the recording played in court so that the jury also could hear it, the prosecution objected to the use of the tape because its admissibility as evidence had not been established. Specifically, the court had to address the fact that the recording was obtained secretly out of court, the participants were not sworn, the witnesses disputed whether or not they recognized even their own voices, and the legal chain of custody had not been demonstrated to ensure ad- missibility of the audio evidence.
The court examined these questions and considered a num- ber of prior federal court rulings, then established what the forensic acoustics community now refers to as the Seven Tenets of Audio Authenticity (United States v. McKeever,
24 | Acoustics Today | Summer 2015
1958): “Current advances in the technology of electronics and sound recordings make inevitable their increased use to obtain and preserve evidence possessing genuine proba- tive value. Courts should deal with this class of evidence in a manner that will make available to litigants the benefits of this scientific development. Safeguards against fraud or other abuse are provided by judicial insistence that a proper foundation for such proof be laid.”
[...]“A review of the authorities leads to the conclusion that, before a sound recording is admitted into evidence, a foun- dation must be established by showing the following facts: (1) that the recording device was capable of taking the con- versation now offered in evidence; (2) that the operator of the device was competent to operate the device; (3) that the recording is authentic and correct; (4) that changes, addi- tions or deletions have not been made in the recording; (5) that the recording has been preserved in a manner that is shown to the court; (6) that the speakers are identified; and (7) that the conversation elicited was made voluntarily and in good faith, without any kind of inducement.”
Since the early 1960s, US Federal Bureau of Investigation (FBI) laboratories have developed techniques and proce- dures for assessing the authenticity and audible contents of forensic audio recordings obtained from law enforcement investigations, and similar capability has been instituted in other public and private forensic acoustics labs around the world (Koenig, 1990). As described in Modern Audio Forensics: Digital “Good” and Digital “Bad,” tenet 3, au- thenticity determination, has become more difficult in our era of read/write digital recording and computer processing compared with the historic reliance on physical analog mag- netic tapes.
Forensic Acoustics and Watergate
A significant turning point in the practice of forensic acous- tics in the United States occurred 15 years after McKeever during the Watergate scandal. In 1971, late in his first term in office, President Richard Nixon directed the Secret Ser- vice to install audiotaping systems in the Oval Office and the Cabinet Room of the White House, in the president’s private office in the Executive Office Building (EOB) next to the White House, and at Camp David, the president’s re- treat in rural Maryland. The existence of these recording systems was known only to a select group of individuals and to the Secret Service (Nixon Presidential Library and Museum, 2015). President Nixon presumably assumed that the recording system's existence would be of interest to no
Spring 2020, Special Issue | Acoustics Today | 25 Reprinted from volume 11, issue 3

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