Audio forensics uses scientific investigation and technology to determine the authenticity of sound in legal cases. It has a long history with the US military and government, and is commonly used to analyze messages created by terrorists. Techniques include comparing unknown sounds with known ones and analyzing signatures from specific sources. Despite the availability of digital tools, evaluating audio remains a time-consuming process.
Audio forensics is simply the use of scientific investigation, technology and tools to determine the authenticity of sound in civil or criminal cases. Audio forensic analysis results can be used as evidence in various legal cases dealing with anything from divorce to industrial espionage. It is also not uncommon to see audio forensics applied to surveillance tapes used in cases against employers or employees of a particular company.
Audio forensics has a long history with the US military and government. In World War II, the technology was used to identify the voices of enemies sounded over radios and telephones. The use of a sound spectrograph, which represented the frequencies and amplitudes of the voice patterns, helped the analyzers to identify persons of interest. In recent years, audio forensics has been used to analyze messages created by terrorists to help identify their locations, the time the audio was created, and other source factors.
Some of the things commonly evaluated in an audio clip to determine its authenticity are background noise, voice frequency changes, noise coming from recording equipment, and stop, start, and pause signatures. Any discontinuity in these areas can signal to the analyzer that the recording is inauthentic or has been compromised. Sometimes these discontinuities can be hidden behind background sounds and extra work is needed to discover them.
One of the most popular techniques used during analysis is to compare an unknown sound with a known one to identify it. This can be done in cases involving voices where one speaker has been identified but the other has not. With voices, prosody, formant vowel trajectory, pitch striations, breathing patterns, nasal resonances, speech pathologies and much more can be used to identify speakers. However, voice identification is still a complex and controversial issue, and many feel that identification and recognition in forensic analysis is inappropriate for presentation in court and lacks credibility.
Forensic audio analysis also emphasizes the use of signatures. Many audio forensics analysts rely on audio signatures coming from specific controlled sources. An example of this is when an audio analyzer uses frequencies from electrical power sources in its work. For these types of analyzers, an electrical outlet can provide all the answers to your audio forensic questions.
Although there are now many digital tools and programs available to a forensic analyzer, the work involved in evaluating a piece of audio remains high. Analyzers can listen to a single piece of audio hundreds of times. Discontinuity detection can be difficult, but not impossible, for the trained and dedicated audio forensic analyzer.
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