Introduction
In case of any edited or distortion of the tape forensic expert can be called upon to examine tape evidences. Mainly this is done to analyze the temporal sequence of events that is present on the tape I.e. to record start, pause and stop operations of tape. This helps to analyze or in examining of “record event signatures”. Various techniques or methods are used in audio forensic laboratory. This includes aural analysis (critical listening); visual analysis of the time- domain waveform (waveform analysis) & via visual analysis of the bitter pattern of the magnetized surface of the tape (magnetic development).
Beside this, forensic expert also asked to examine the record to analyze whether the record was edited or whether it is original recording or it is intimated. Tape recordings are dependent more on false information i.e. forgery or interpret wrongly, mainly in advent of computer- based digital editing appliances. It is very significant in both legal practitioner and examiner to interpret forgery or interfere effort with tapes includes an purposeful interfere to change tape’s original contended.
The human being has good ability to identify familiar voices and the result of automatic speaker recognition are fair in controlled conditions, but these circumstances are rarely reached in real forensic cases. The speaker recorded from the telephone line in a kidnapping or blackmail case is often stressed or afraid, and unfamiliar to police.
Voice as Evidence
The evidence is the energy in the form of mechanical, electrical or magnetic which is converted from a acoustic energy by a transducer.
It is not a speech itself. It is stored in the storage medium which can be coded by an analog or digital information coding method.
Waveform Analysis
It starts with the actual proof of the playback had to be stored digitally in computer with the help of original recording as it contain similar head configuration. For example:- ¼ track stereo cassette tape is one of the most famous formats is played back for digital storage and analysis on a computer using ¼ track stereo cassette tape machine.
A high quality tape recorder is a computer with graded good quality analog- digital converters and suitable software. Formerly attain, waveform editor of audio recording uses markedly clarify navigation all over the consistent, duplication of audio carry on the whole proof tape, and critical listening can be merge with visual analysis to mark significant activities further examination.
Using waveform analysis, experts can easily observed many more types of record event signatures, record stops as feature large peak of the record of the record head electrical discharge, followed by the low frequency erase head discharge. Sometimes pause signatures can also be analyze but generally it fails. Generally, waveform analysis permit a comparatively simple means for examining discontinuous across long recordings, which can be analyzed from either the presence of signatures, just discussed, and/or from changes in background noise.
Video and Audio Evidence Enhancement
The main motive of using audio recording or security camera system is to record evidence or significance. But when situation is out of control obstruct with the listener or viewer’s ability to acknowledge action or dialogue, or to find persons and things, the proof could show pointless without enhancement.
Importance of Video and Audio Tape Authentication
Whenever it is introduced in legal proceedings, it is the fact that it will be questioned and will require some authentication. Sometimes a simple chain of custody proof is enough; if not then some other technical measures are required. Often, there are circumstances where in both inside and outside of the courtroom, it is viable that damage brings major doubt on a specific video or audio tape unless proper authentication has been conducted. This has been analyzed by forensic expert of the original digital or analogue recordings, our technical expert will record and examine to the indication which suggest damage has occurred.
Conclusion
Eventually, the FBI recommends a physical as well as spectrographic (waveform) analysis of the tape to construct a concern decision. The physical analysis includes a up skill evaluator be attentive to understand pitch, quality, rate of speech, mannerisms, amplitude, breathing patterns, fricative couplings, background reverberate alteration, hum and other acoustic event , such as room resonance.
References
- J. Gruber, F. Poza, and A. Pellicano, “ Audiotape Recordings: Evidence, Experts and Technology” American Jurisprudence. Trials. Vol. 48, Lawyers Cooperative Publishing (1993).
- B. Koening, “Authentication of Forensic Audio Recordings” Journal of the Audio Engineering Society vol. 38, no. ½ (1990).
- T. Owen, “Forensic Audio and Video- Theory and Applications” Journal of the Audio Engineering Society vol.36, no.1/2 (1988).
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