Forensic audio deals in the scientific and professional investigation (including the technology and tools used) to determine the authenticity of sound where it pertains to criminal cases, as well civil court cases. Based on audio forensics, the results turned up during investigation can be used as evidence in criminal and civil cases that deal with anything from family and neighbor disputes, divorce, extortion and even industrial espionage.
Audio forensics have been used in virtually every case involving a wiretap or recorded conversation that was used in a trial – and that includes the common analysis of surveillance tapes in work environments, particular with disputes between employers and employees.
The Roots of Forensic audio
Before audio forensics was widely used in the professional world and by law enforcement agencies, the practice was focused mainly among the United States government. Linguistics experts and those versed in studying audio would utilize technology during World War II to dissect and analyze the voice patterns of enemies via radio and telephone.
During World War II, specialists utilized a spectrograph to plot the frequencies and amplitudes of voice patterns. This practice made it easier to identify individuals of interest and monitor frequencies for important broadcasts or intelligence.
Now, these same practices are used with more advanced technology to identify terrorist subjects, reveal their location and discern when the audio was created along with other pertinent factors.
Digging into Audio Forensics
Those analyzing audio don’t just listen to speech. Every noise must be carefully considered with audio files because it could be relevant to the overall recording, encounter, etc. Some of the factors that are commonly evaluated by audio forensic specialists include
- Changes in voice frequency
- Noises emanating from recording devices or other machines
- Background noise and natural artifacts
- Unnatural artifacts
- Pause signatures as well as start and stop points
These are all important points because unnatural noises or an inconsistency in noise patterns could mean the audio was compromised, or that it’s not authentic. There are also factors considered when audio forensics specialists have to identify multiple speakers in meetings where voices carry over one another. Some of the factors they analyze include
- Breath patterns
- Nasal Resonance
- Vowel formation
Audio Forensics and Law Enforcement Transcription
In many cases, law enforcement agencies call upon audio forensic specialists not only to study and dissect recorded audio, but also to provide transcription services. Simply providing a report of the data is not enough in all cases. To be admissible as evidence, a certified transcript of the entire audio recording is required for review.
This can be an exceptional amount of work. Unlike other forms of transcription where only the voice is recorded, law enforcement transcription sometimes requires every sound and artifact to be documented and transcribed. This includes voices, doors opening and closing, chairs scraping across floor, rustling, sighing, lip smacking, papers being shuffled, etc.
Each one of these noises could provide insight into an interrogation, meeting, or encounter that may not typically be picked up by the untrained ear. Detection of these noises, as well as discontinuities in other types of recordings can be difficult, but certainly not impossible for those who specialize in audio forensics.