Page 28 - Special Issue
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Forensic Acoustics
recorders clipped to the vests of law enforcement officers
Analysis of the four audio channels of CVRs primarily in-
of acoustical events, and educate the attorneys, defendants, to document their interaction with the public. As recorder
1958): “Current advances in the technology of electronics volves transcribing the spoken words of the pilot and copi-
judges, and juries about the meaning, significance, and limi- costs continue to decrease, it seems inevitable that more and
and sound recordings make inevitable their increased use lot, and any other utterances by members of the crew. In ad-
tations of the recorded evidence (Audio Engineering Soci- more investigations will include evidence obtained from
to obtain and preserve evidence possessing genuine proba- dition to the flight crew's speech, the microphones can also
ety, 1996; Maher, 2009). Figure 2 depicts an interpretive an- these portable devices and dashboard recorders (McGinty, 2015).
tive value. Courts should deal with this class of evidence in pick up nonspeech sounds that can be very important to
notation that has been added to a time waveform to assist
a manner that will make available to litigants the benefits accident investigators. Engine sounds, airframe vibrations,
The ubiquity of audio recording devices will require an with an investigation.
of this scientific development. Safeguards against fraud or avionics audible warning alarms, and sounds of cockpit in-
emerging specialty in handling, searching, and analyzing the potentially huge number of recordings available from
other abuse are provided by judicial insistence that a proper trusions or other commotion may all have significance to
Forensic Acoustics and the US Courts
foundation for such proof be laid.”
the investigation. For example, the March 2015 demise of
a public incident that leads to a forensic investigation. The Audio forensics traces its origins to the development of por-
Germanwings Flight 9525 in the French Alps has been at- [...]“A review of the authorities leads to the conclusion that,
investigative challenge that occurred after the 2013 Boston table recording equipment, and examples of the use of audio
tributed to deliberate action by the copilot reportedly based before a sound recording is admitted into evidence, a foun-
Marathon bombing involving dozens of surveillance record- recordings in US courts date to the mid-1950s. Although the
in large part on preliminary evaluation of the CVR evidence. dation must be established by showing the following facts:
ings and hundreds of digital photos taken by smartphone courts generally began to accept the unique importance of
What’s more, even the sound of the pilots’ respirations can (1) that the recording device was capable of taking the con-
and camera-toting bystanders near the finish line provides a audio recordings, especially in cases involving speech ob-
give information about the flight crew’s health, state of alert- versation now offered in evidence; (2) that the operator of
glimpse of what is likely to occur in future incidents involv- tained via clandestine surveillance or wiretaps, there were
ness, and level of anxiety or agitation (Stearman et al., 1997; the device was competent to operate the device; (3) that the
ing video, audio, and still photo evidence (NOVA, 2013). significant considerations regarding the Fourth Amend-
Byrne, 2002; McDermott, personal communication). recording is authentic and correct; (4) that changes, addi-
ment’s protections against unreasonable searches and sei-
Transportation Accident Investigations:
tions or deletions have not been made in the recording; (5) CVR systems are typically activated automatically whenever
that the recording has been preserved in a manner that is the aircraft is powered up, whereas the FDR systems collect
shown to the court; (6) that the speakers are identified; and flight data only from the point at which the plane becomes
(7) that the conversation elicited was made voluntarily and airborne. This means that the CVR may contain important
in good faith, without any kind of inducement.” information about flight crew checklist completion, preflight
zures and concern about the legal admissibility of a record-
The Cockpit Voice Recorder
ing as being a bona fide representation of the sonic events Because commercial aircraft accidents are so remarkably
actually present during the recording process.
infrequent, aviation regulatory agencies can afford to spend
substantial resources to investigate the cause of accidents
The McKeever Case
when they do occur. Arguably the most important develop- Among the key cases in the US federal court system regard-
ment in accident investigations today is the invention of the ing the admissibility of audio forensic evidence is United
flight data recorder (FDR) and cockpit voice recorder (CVR) States v. McKeever (1958). In the McKeever case, two de-
equipment required on all civilian commercial passenger fendants were indicted for extortion in an antiracketeering
flights, large private jets, and many military flights, the so- prosecution involving the International Longshoremen’s
called “black boxes” (National Transportation Safety Board, 2015). Association. After his indictment, the defendant McKeev-
discussion, and similar audio information obtained before Since the early 1960s, US Federal Bureau of Investigation takeoff that isn't covered by the FDR information (McDer- (FBI) laboratories have developed techniques and proce- mott, personal communication).
er had arranged to make a surreptitious tape recording of Originally developed using special fireproof magnetic tape,
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ijnectothoetrhepusabmlice avnaldidpitryivcaotne sfiodreernatsiocnascuosuesdticfos rlaobths earrotyupneds
tohfescwieonrltdifi(cKeoxepneirgt,is1e9b9e0f)o.rAesthdesicnrfiobremdaitnioMn ocadnerbneAstuadteiod
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ceorsmbpoatrhedciwviilthtritahles hanisdtocrricimreinlianl pcerosnecpuhtyiosincsalinantahleogfemdearga-l
ncoeutirctsta),p“eThs. e Rules—especially Rule 702—place appropriate
a conversation he had with an individual who later was a contemporary FDRs and CVRs now record in digital form
witness in the trial. During the trial, McKeever’s defense using nonvolatile solid-state memory. FDR systems on con-
team sought to challenge under cross-examination the wit- temporary airliners can record hundreds of flight param-
ness’ testimony by playing a portion of the clandestine tape eters, actuator positions, and sensor readouts every second,
recording to refresh the witness’ recollection. The court al- with memory capacity for up to 25 hours. Yet, even with
lowed the tape to be played but only via headphones so that the plethora of flight data, the acoustical information from
limits on the admissibility of purportedly scientific evidence
the witness could hear it but not the jury. When the defense the CVR is often indispensable for accident investigators to
Forensic Acoustics and Watergate
then sought to have the recording played in court so that piece together what happened leading up to the accident.
by assigning to the trial judge the task of ensuring that an
the jury also could hear it, the prosecution objected to the
A significant turning point in the practice of forensic acous- expert's testimony both rests on a reliable foundation and
CVRs capture four separate monophonic channels: the pi- use of the tape because its admissibility as evidence had not
tics in the United States occurred 15 years after McKeever is relevant to the task at hand” (Daubert v. Merrell Dow,
lot’s headset microphone, the copilot’s headset microphone, been established. Specifically, the court had to address the
during the Watergate scandal. In 1971, late in his first term 1993). Assessing the reliability of audio forensic opinions
a cockpit area microphone (CAM) mounted in the cockpit’s fact that the recording was obtained secretly out of court, the
in office, President Richard Nixon directed the Secret Ser- can be a challenge. Unlike DNA comparisons that can be
ceiling panel, and the fourth channel that often is used to participants were not sworn, the witnesses disputed whether
vice to install audiotaping systems in the Oval Office and expressed in a formal statistical sense, a forensic acoustics
record the intercom communications between the pilots and or not they recognized even their own voices, and the legal
the Cabinet Room of the White House, in the president’s question such as “Is the utterance present in the evidentiary
the flight attendants. Modern CVRs record up to 120 min- chain of custody had not been demonstrated to ensure ad-
private office in the Executive Office Building (EOB) next recording the voice of Suspect A?” traditionally has not been
utes of audio in a memory buffer loop, sequentially over- missibility of the audio evidence.
to the White House, and at Camp David, the president’s re- amenable to having a strong statistical basis for the opinion.
writing the oldest data with new data. Thus, in the event of
treat in rural Maryland. The existence of these recording Due to growing judicial skepticism about the scientific ba-
The court examined these questions and considered a num- an accident, the audio forensic examiner will have a record-
systems was known only to a select group of individuals sis for almost all forensic testimony in fields ranging from
ber of prior federal court rulings, then established what the ing containing the sounds from the 2 hours preceding the
and to the Secret Service (Nixon Presidential Library and fingerprints and bite marks to handwriting and carpet fiber
forensic acoustics community now refers to as the Seven crash (National Transportation Safety Board, 2007).
Museum, 2015). President Nixon presumably assumed that comparisons, the 2009 report by the National Academy of
Tenets of Audio Authenticity (United States v. McKeever,
the recording system's existence would be of interest to no
28 | Acoustics Today | Spring 2020, Special Issue
Summer 2015 | Acoustics Today | 27
24 | Acoustics Today | Summer 2015 Reprinted from volume 11, issue 3
dures for assessing the authenticity and audible contents of
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