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Germanwings Flight 9525 that crashed in the French Alps in March 2015. Forensic acoustics comes into play also when there is a dispute about the likelihood that an acoustical product presents a hearing hazard or interferes with the audibility of an aural emergency notification alarm. The domain of forensic acoustics even includes forensic musicology for cases of alleged copyright infringement of musi- cal style and intellectual property (Be- gault et al., 2014). The impact of forensic musicology was evident in the recent suc- cessful litigation award of US$7.4 million in damages a court ruled must be paid by entertainers Robin Thicke and Phar- rell Williams to the heirs of the late singer Marvin Gaye.
Figure 2. Example of a forensic audio recording, with manual annotation, displayed with a sound software package. It depicts the amplitude vs. time waveform of approximately one minute of audio recorded at an emergency dispatch center and includes utterances from the land mobile radio system and the local voice of the dispatcher. Figures like this allow experts in forensic acoustics inform and educate attorneys and "triers of fact" (e.g., judge, jury, designated administrator) who are likely inexperienced with forensic audio interpretation.
Despite its occasional high profile, forensic science has come up against some serious scrutiny and soul searching in re- cent years, including an influential 2009 report from the US National Research Council that criticized many forensic fields, including audio forensics, for lacking scientific evalu- ation of reliability and error rates (National Academy of Sci- ences, 2009). Thus, it is increasingly important that the sci- ence in forensic investigations be based on unquestionably objective interpretation and not merely subjective opinions, as has sometimes been the case.
I begin with a description of several key elements, terms, and historical origins of forensic acoustics, primarily in terms of the judicial system in the United States. Next, I consider the challenge of determining authenticity in the age of digital data storage and the corresponding opportunities present- ed by the increasingly wide deployment of audio recording apparatus in memo recorders, digital cameras, and virtu- ally every contemporary smartphone. Finally, I sum up the field by mentioning areas in which interested members of the Acoustical Society of America (ASA) can get involved to provide new and innovative research that will help advance forensic acoustics.
What Is Forensic Acoustics?
Forensic acoustics, or audio forensics, is the specialty field of acoustics and audio engineering that deals with the ac- quisition, analysis, and evaluation of audio recordings that are to be presented as evidence in an official inquiry or in a court of law (Maher, 2009). In addition to the analysis and
interpretation of tangible audio recordings, forensic acous- tics may also treat questions of audibility in the context of litigation or criminal prosecution, such as civil annoyance complaints from an outdoor performance venue, noise lev- els produced by takeoffs and landings at an airport that vio- late local statutes, or whether or not a scream or other sound was likely to have been detectable under the circumstances claimed by an ear witness.
Forensic acoustics experts who deal with recorded evidence are most often consulted about three concerns: authenticity, enhancement, and interpretation (Maher, 2010).
Authenticity denotes the acceptance of a recording as being unaltered and true to its source and chain of custody. Crim- inal and civil cases may hinge on a dispute about the cir- cumstances under which a recording was made and whether audible material in the recording could have been deleted, added, or otherwise edited after the fact (Koenig 1990; Au- dio Engineering Society, 2000).
Enhancement involves signal-processing techniques that at- tempt to improve the intelligibility of speech, the clarity of specific background sounds, or the overall signal-to-noise ra- tio of the recording. Modern enhancement techniques use a high-quality digital copy of the original recording so the origi- nal recording medium is used only to obtain the work copy for enhancement (Musialik and Hatje, 2005; Koenig et al., 2007).
Finally, interpretation refers to the description of the acous- tical evidence in words, pictures, statistics, and graphs that help address investigative questions, explain the sequence
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