Bruce E. Koenig

An inconclusive digital audio authenticity examination: a unique case.

Abstract:  This case report sets forth an authenticity examination of 35 encrypted, proprietary‐format digital audio files containing recorded telephone conversations between two codefendants in a criminal matter. The codefendant who recorded the conversations did so on a recording system he developed; additionally, he was both a forensic audio authenticity examiner, who had published and presented in the field, and was the head of a professional audio society’s writing group for authenticity standards. The authors conducted the examination of the recordings following nine laboratory steps of the peer‐reviewed and published 11‐step digital audio authenticity protocol. Based considerably on the codefendant’s direct involvement with the development of the encrypted audio format, his experience in the field of forensic audio authenticity analysis, and the ease with which the audio files could be accessed, converted, edited in the gap areas, and reconstructed in such a way that the processes were undetected, the authors concluded that the recordings could not be scientifically authenticated through accepted forensic practices.

The average direct current offset values for small digital audio recorders in an acoustically consistent environment.

In this research project, nine small digital audio recorders were tested using five sets of 30‐min recordings at all available recording modes, with consistent audio material, identical source and microphone locations, and identical acoustic environments. The averaged direct current (DC) offset values and standard deviations were measured for 30‐sec and 1‐, 2‐, 3‐, 6‐, 10‐, 15‐, and 30‐min segments. The research found an inverse association between segment lengths and the standard deviation values and that lengths beyond 30 min may not meaningfully reduce the standard deviation values. This research supports previous studies indicating that measured averaged DC offsets should only be used for exclusionary purposes in authenticity analyses and exhibit consistent values when the general acoustic environment and microphone/recorder configurations were held constant. Measured average DC offset values from exemplar recorders may not be directly comparable to those of submitted digital audio recordings without exactly duplicating the acoustic environment and microphone/recorder configurations.

Identification of an eccentricity in the date/time metadata of a PAL MiniDV recording.

Abstract:  A Phase‐Alternation Line (PAL) Mini Digital Video (MiniDV) recording and camcorder were provided by the Law Society of Singapore for forensic examination. During visual analyses of the submitted recording and a test recording produced on the submitted camcorder, the number of occurrences of each unique date/time stamp varied from the nominal value of 25 frames (the frame rate per second of PAL recordings), within a range of ±3 frames. This embedded date/time information is recorded in the digital bit stream along with the video and audio information and can be optionally displayed during playback. These visual observations prompted detailed analyses of the digital metadata of the recordings which consisted of locating the portions of the bit stream associated with the date/time information, and then identifying their redundancy characteristics, data structure, and encoding protocol. Automated scripts were developed using digital data analysis software to locate, extract, convert, and count all of the unique date/time stamps, and to provide an easily‐viewable output of the results. The application of the scripting process to both the submitted tape and the test recording produced on the submitted camcorder revealed that the date/time information on each exhibited a nonstandard but consistent timing pattern, which confirmed the visual observations and provided evidence that the submitted recording was consistent with having been produced on the submitted camcorder.