To determine whether or not a tape has been edited, tampered with or altered in any way. The output signals of tape recorder can be damaged by three general factors - noise, interference and distortion. Each of which is caused by a specific condition. In addition, there is what Cain calls “adverse forensic influences” that include the bandwidth equalization of telephone lines that limit voice frequencies between 300 to 3500 Hz. To reduce or eliminate various noise and distortion sounds from an audio tape, forensic audio specialists use a variety of filters. Therefore, when a tape hiss occurs within the speech frequency range, a so-called low-pass filter is used to eliminate it. The tape enhancement process, therefore, must start with examination of the equipment used for analysis. Once a tape is cleansed of interfering noises to make the recorded voices or other pertinent sounds as clear as possible, it usually must be authenticated before it can be introduced as evidence before court to avoid any charges of illegal tampering.
Video authentication is a process that is used to ascertain the trustworthiness of a digital video. In other words, a video authentication system ensures the integrity of digital video, and verifies that the video taken into use has not been tampered.
Forensic Video Examinations
The forensic video examiner is concerned with the authenticity and integrity of the signal. Questions relating and whether the tape is a copy, a compilation of other tapes or an edited version are of important consideration. Forensic examinations of videotapes usually consist of both a visual and aural examination. One of the more important pieces of equipment used in forensic video examinations are a waveform monitors which is a specialized oscilloscope. It displays the voltage versus time modes and has specialized circuits to process the signal. If any editing occurs, then it’s possible to display the signal aberration on the display screen of the instrument.
The use of auditory analysis, acoustic analysis and/or computerized techniques to recognize, identify or discriminate among human voices. A human voice is as unique to an individual as a fingerprint. This makes it possible to identify a speaker and to record the characteristics of his or her voice for use as the base for future verification, identification of a person from the sound of their voice. Speaker identification is the way of identifying a person solely by their speech. Forensic speaker identification usually consists of both aural and spectrographic analysis of voice. Various steps such as digitization, segregation, clue word formation etc. are involved. The spectrographic test involves testing of various parameters such as frequency, pitch, energy, amplitude in voice signal. The level of noise involved also affects the result. Different filters are applied to remove noise such as broad band filters.