NCJ Number
225771
Journal
Journal of Forensic Identification Volume: 59 Issue: 1 Dated: January/February 2009 Pages: 97-126
Date Published
January 2009
Length
30 pages
Annotation
This study analyzed 15 nonstandard head parameters on 8 NTSC (National Television Standards Committee) video cassette recorders, using 112 test recordings, in order to determine whether they were useful in matching a particular recording to a specific VHS unit.
Abstract
The study identified four head parameters that were useful for identifying the VHS unit that made a recording of interest in an investigation. One parameter is the playback time between the end of the hi-fi audio and the linear audio erase head. A second parameter is the playback time between the end of the hi-fi audio and the full-track erase head. A third parameter is the playback time between the linear audio and the full-track erase heads; and the fourth parameter is the waveform signature of the linear audio erase head. Three additional parameters were found to be comparable with only certain recorders. The eight remaining parameters examined were not sufficiently distinct for most forensic applications. The testing made no attempt to account for the wide range of variables that might influence how video and audio signals are recorded onto a tape. The authors advise that when comparing submitted recordings or test recordings prepared on a submitted recorder, the examiner should use normal forensic audio-video procedures and standards. Thirteen of the especially important features of the procedures and standards are listed. This report lists the 15 parameters measured for the nonstandard VHS head parameters. The procedures used in conducting the test recordings on the eight VCRs are described, along with the procedure for examining the test recordings. 5 figures and 11 references, 12 tables