Equipping the Modern Audio-Video Forensic Laboratory

Article excerpt


Establishing or increasing the capability of a modern forensic audio-video laboratory draws on diverse disciplines including physics, electrical and electronic engineering, computer science, analog and digital theory, acoustics, digital signal analysis, digital imaging, and other related fields. These disciplines require a wide variety of electronic equipment to enable a forensic examiner to conduct reliable examinations. This paper is directed toward established laboratories that have limited audio-video capability but may be required to increase audio-video forensic support.

The following factors should be considered when establishing or increasing the capability of a modern audio/video forensic laboratory:

* Identifying potential employees

* Requiring a lengthy apprenticeship or equivalent experience of personnel in certain audio and video analyses fields

* Obtaining specialized training in such areas as digital signal analysis, recording theory, sound measurement, and video imaging

* Seeking support and guidance from other established laboratories

* Equipping the laboratory to play back and record in numerous analog and digital audio and video formats, and then providing the capability to improve voice intelligibility, compare voices, identify non-voice signals, authenticate recordings, enhance video images, and conduct other related analyses

* Procuring professional audio, video, enhancement, signal analysis, imaging, and other related equipment

* Identifying physical space for the laboratory

This paper will concentrate on the last three items in the list by discussing eight audio-video examinations, the identification and costs of equipment needed to examine audio-video evidence, and laboratory-space considerations. Examination procedures and personnel matters will not be addressed.

Audio-Video Examinations

Modern audio-video forensic laboratories are capable of analyzing analog or digital audio-video recordings to support criminal investigations, governmental intelligence, civil litigation, personnel and administrative matters, and other related issues. Some laboratories conduct a wide range of examinations on audio and video recordings, whereas others provide only duplication and a few other commonly requested analyses.

The eight most commonly conducted audio-video examinations are listed below, with the level of complexity from lowest to highest:

* Playback and duplication: The capability to play back recordings and provide high-quality, readily useable duplicates on standard formats. A fully equipped laboratory can work with most audio-video formats as well as specialized recordings (e.g., miniature law enforcement formats, 911 logging recordings, time-lapse video).

* Repair: The capability to repair torn or stretched tapes in standard audio-video analog and digital formats

* Audio enhancement: The capability to improve the voice intelligibility of recordings and to prepare enhanced copies of audio recordings and the audio information on video formats

* Voice identification: The capability to compare unknown recorded voices to known voice exemplars by identifying similar and dissimilar characteristics

* Video image duplication and enhancement: The capability to duplicate or improve video recordings

* Signal analysis: The capability to quantify, identify, and compare non-voice signals to determine origin and characteristics (i.e., telephone signaling, gunshot sounds)

* Authenticity: The capability to resolve the authenticity of audio-video recordings by determining originality, continuity, and integrity

* Digital data analysis and retrieval: The capability to extract and analyze digital audio-video recordings on commercial and proprietary recording devices

Equipment and Costs

The equipment requirements for the eight audio-video forensic examinations are listed below. …