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| Improved NIST tape analysis shows tampering in detail |
| by GV staff |
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July 30, 2007
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The National Institute of Standards and Technology has developed an improved version of a real-time magnetic microscopy system that converts evidence of tampering on magnetic audio and videotapes -- erasing, overdubbing and other alterations -- into images with four times the resolution previously available.
This system is much faster than conventional manual analysis and offers the additional benefit of reduced risk of contaminating the tapes with magnetic powder. NIST recently delivered these new capabilities to the FBI for validation as a forensic tool.
Earlier versions of this system made images with a resolution of about 400 dpi, but the new system uses four times as many magnetic sensors embedded on a NIST-made silicon chip that serves as a read head in a modified cassette tape deck. The NIST read head operates adjacent to a standard read head, enabling investigators to listen to a tape while simultaneously viewing the magnetic patterns on a computer monitor.
Each sensor in the customized read head changes electrical resistance in response to magnetic field patterns detected on the tape. NIST developed the mechanical system for extracting a tape from its housing and transporting it over the read heads, the electronics interface, and software that convert maps of sensor resistance measures into digital images.
The upgrade included quadrupling the image resolution to 1600 dpi, the capability to scan both video and audio tapes, complete computer control of tape handling, and the capability to digitize the audio directly from the acquired image. The software displays the audio magnetic track pattern from the tape to identify tiny features, from over-recording marks to high-intensity signals from gunshots. The system is designed to analyze analog tapes but could be converted to work with digital tapes, according to project leader David Pappas.
The FBIs Forensic Audio, Video and Image Analysis Unit receives hundred of audio tapes for analysis annually. The FBI provided partial funding for development of the NIST tape imaging systems.
MORE INFO
NIST nist.gov
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