This audio podcast from the "Just Science" research and development symposium for forensic science professionals consists of an interview with Dr. Rob Maher, in which he explains his research in and features of gunshot acoustics, which focuses on the interpretation of the characteristic sounds produced by firearms recorded at a crime scene.
Dr. Maher's research and teaching interests are in the area of digital signal processing, with emphasis on applications in digital audio, audio forensic analysis, digital music synthesis, and acoustics. In the interview, Maher notes that audio forensic evidence is increasingly common in law enforcement investigations because of the growing availability of inexpensive and lightweight digital voice recorders and miniature personal digital video camera systems for routine law enforcement and surveillance. He indicates that the acoustical characteristics of a firearm depend on the type of gun and ammunition that produces the sound, the distance and azimuth with respect to the gun barrel, and the acoustical reflections and reverberation due to nearby surfaces and objects. For scientific study, the direct sound of the muzzle blast must be separated from the acoustic reflections, echoes, and reverberation caused by the recording environment. In this research, the team uses an elevated array of 12 specialized microphones capable of capturing the high intensity and short duration of the firearm's muzzle blast concurrently over 180 degrees in azimuth. Each microphone is recorded with 16-bit resolution at a 500 kHz sampling rate, and the elevated platform enables the entire muzzle blast to be recorded before the arrival of the first acoustical reflection from the ground. Recommendations are offered on the use and processing of the database of firearm acoustical recordings, and the future prospects for forensic gunshot acoustical analysis are discussed.
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