NCJ Number
113144
Journal
Crime Laboratory Digest Volume: 15 Issue: 2 Dated: (April 1988) Pages: 44-54
Date Published
1988
Length
11 pages
Annotation
Law enforcement agencies have increased their use of inexpensive, miniature and slow-speed standard analog tape recorders to collect audio evidence in civil and criminal investigations.
Abstract
These recorders have a variety of shortcomings, including an increased susceptibility to misalignment of the record track azimuth that can produce severe signal and intelligibility losses on playback. Azimuth misalignment (AM) problems occur when a three-head tape recorder with separate record and reproduce heads or two different tape recorders are used. Degree of signal loss will depend upon the width of the reproduce head, the speed of the recording, the quality of head mountings, the time since last maintenance, and the frequency range of pertinent audio information. In the forensic laboratory, two AM problem areas are often confronted: playback of original recordings and preparation of high quality copies for analysis. While playback on the original recorder will eliminate AM problems, special laboratory recorders are preferred because they have higher audio quality, often incorporate speed adjustments, and permit adjustment of the azimuth through alignment of the reproduce head. Checking for AM of recordings may be accomplished through microscopic examination, frequency-domain analysis, and manual reproduce head adjustment. Forensic tapes should be checked for correct azimuth alignment before conducting enhancement voice comparison, authenticity tests, and other analyses. 9 figures and 8 references.