The machine will produce a spectrogram in approximately eighty seconds. The finished product is called a spectrogram and is a graphic depiction of the patterns, in the form of bars or formants, of the acoustical events during the time frame analyzed. This process is repeated until the entire desired frequency range is analyzed for that portion of the recording. This instrument then analyses the next small frequency range and samples and marks the energy levels at that point. The analog sound spectrograph samples energy levels in a small frequency range from a magnetic tape recording and marks those energy levels on electrically sensitive paper. The analog spectrograph is composed of four basic parts (1) a magnetic tape recorder/playback unit, (2) a tape scanning device with a drum which carries the paper to be marked, (3) an electronic variable filter, and (4) an electronic stylus which transfers the analyzed information to the paper.
The instrument produces a visual representation of a given set of sounds in the parameters of time, frequency and amplitude. It has been widely used for the analysis and classification of human speech sounds and in the analysis and treatment of speech and hearing disorders. The sound spectrograph, an automatic sound wave analyzer, is a basic research instrument used in many laboratories for research studies of sound, music and speech. The majority of courts hearing the issue have admitted spectrographic voice identification evidence. Exclusion has always been based on the fact that the evidence presented did not present a clear picture of the technique’s acceptance in the scientific community and as such, the court was reluctant to rely on that evidence. Although many courts have denied admission to voice identification evidence, none of the courts excluding the spectrographic evidence have found the technique unreliable. Even those courts which have claimed to use the same standard of admissibility have interpreted it in a variety of ways resulting in a lack of consistency. To compound the problem, courts have utilized different standards of admission resulting in different opinions as to the admissibility of voice identification evidence.
#Music spectrograph decibel range trial#
Trial strategies and budgets have resulted in incomplete pictures for the courts. Many courts have had to rule on this issue without having access to all the facts. The road to admissibility of voice identification evidence in the courts of the United States has not been without its potholes. Both aural and spectrographic analysis are combined to form the conclusion about the identity of the voices in question. No longer limited to the visual comparison of a few words, the comparison of human voices now focuses on every aspect of the words spoken the words themselves, the way the words flow together, and the pauses between them. Voice identification experts are found all over the world. The research, which is still continuing today, demonstrates the validity and reliability of the process when performed by a trained and certified examiner using established, standardized procedures. Today voice identification analysis has matured into a sophisticated identification technique, using the latest technology science has to offer. Thus the battle lines were drawn over the admissibility of voice identification evidence with proponents claiming a valid, reliable identification process and opponents claiming more research must be completed before the process should be used in courtrooms. They felt that the technique should not be used in the courtroom without more documentation. Gradually the process became known to other scientists who voiced concerns, not as to the validity of the analysis, but as to the lack of substantial research demonstrating the reliability of the technique. Due to the newness of the technique there were only a few people in the world who performed voice identification analysis and were capable of explaining it to a court.
Voice comparisons were made solely on the pattern analysis of a few commonly used words. There was also no standardization of how an identification was reached, or even training or qualifications necessary to perform the analysis.
In the early days of this identification technique there was little research to support the theory that human voices are unique and could be used as a means for identification. The forensic science of voice identification has come a long way from when it was first introduced in the American courts back in the mid 1960’s.
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