| Audio recordings of acoustic events that include conversations, interviews, interrogations, wiretaps, surveillance situations, etc., are increasingly stored in a digital format. While digital recording has been possible for several decades, the technology is now ubiquitous in the form of recordable optical discs (CD-R, CD-RW, DVD, etc.), handheld digital voice recorders, digital voicemail services, mobile smart phones with voice notes/memo features, digital audio workstations (DAWs) that record to computer hard drives (hard disk or solid-state) , and other types of media that store binary audio information. Digital media offers many advantages over analogue, including better signal-to-noise ratio, fewer mechanical noises, longer battery life, and more, but it also makes proving authenticity much more challenging. This is particularly important when conducting forensic examinations involving criminal or civil cases. The fact that perfect clones are possible, combined with the relative ease of manipulating or editing digital recordings that sometimes defy aural detection, makes authentication a difficult process.;At present, no national or international standard exists for proving digital audio authenticity. There is neither a standard for defining "authentic" digital recordings (previous standards are for analogue), nor is there a standard means for presenting the findings of an expert. This lack of agreement is probably due to the difficulty in drawing generalizations in a discipline where every case is unique (to some degree), the technology is rapidly changing, and there is no examiner certification process or licensing board (aside from some advisory and technical committees with no regulatory authority). With some notable exceptions, relatively few articles and best practices guidelines have been published on digital audio authenticity. This paper examines some current and emerging techniques, to attempt to come closer to a reliable standard for digital audio authentication. Beyond the techniques themselves, which are sure to change, the paper critically analyzes the thought process that occurs during authenticity analysis: what the examiner learns (or does not learn) from each technique, the role that interpretation plays in guiding him to his ultimate conclusion, and the means of presenting findings in a clear, unbiased manner that do not overstate the scientific certainty of conclusions. |
