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What is Forensic Audio Analysis?

Forensic Audio Analysis is the process of investigating a recording to determine the authenticity of the events. In other words, this process verifies the integrity of the evidence. Throughout the audio analysis process, we also determine if the recording is consistent with a digital original, unaltered recording.

Primeau Forensics performs extensive audio authentication of both the audio content through electronic measurement and metadata analysis..?So why is forensic audio authentication so important in forensic audio analysis? What should an audio forensic expert be aware of when examining audio evidence? What is the process of examining and authenticating audio evidence?

Digital Evidence Integrity

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The audio authentication process determines whether or not the audio recording in question has been tampered with. In this age of digital audio, edits can be made and covered up very easily. There are free versions of audio editing software – such as Audacity ? which are available on line and can make edits that alter the events or conversation that originally occurred in digital audio recordings.

If audio evidence is found to be altered through forensic audio authentication, it should be ruled inadmissible in court because it is not an accurate representation of the events that occurred.

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Audio Analysis in Litigation

When one of the parties in a litigation believes that an audio recording was tampered with or edited, an audio forensic expert is brought in to investigate the recording.?The investigations we perform include careful analysis of every aspect of an evidence file to guarantee an accurate investigation.? We understand the weight our conclusions may have in a litigation and therefore give the utmost attention to detail for every investigation.?

When performing forensic audio analysis, the first step is to establish a chain of custody. A chain of custody does not, in and of itself, establish a recording as being authentic. Audio evidence preserved in the original device can still be deemed as not authentic.

Electronic Measurement

After critical listening, the forensic expert must use electronic measurement to examine the audio evidence. This is done by noting the prominent frequencies in the voices or other sound source and the noise floor.

The levels of the recording and of the different frequencies can be measured as well. Tools such as spectrograms, frequency analysis windows and level meters are very helpful for observing and collecting this information. The expert should note the frequency range of the overall recording, the voices or conversation and the noise floor or extraneous sounds in the recording.

If the frequency range of a voice suddenly becomes larger or smaller or shifts in frequency range, that can be a sign of an edit. Sudden, unexplained changes in the noise floor level as well as the sudden presence of another background noise can also be a sign of an edit. As I mentioned before, I have come across recordings in which I could hear two noise floors. This can often be measured and seen in a spectrogram and a frequency analysis panel.

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Analyzing Audio Metadata

Digital audio recordings contain metadata which reveals information about how the recording was made and the type of equipment that created the recording. If third party software is identified in the metadata then that footprint is observed and reported indicating the name of the software. Third party software is often capable of performing edits.

When examining the digital information, it is necessary to create an exemplar recording to compare the metadata with the original. An exemplar is a recording that is made in conditions that are as close to the original recording as possible . The exemplar is made on the same kind of audio recorder and, if possible, the same environment. Using this exemplar, the forensic expert can compare the metadata and HEX information of the two files.

If you have an audio recording that you question or need help understanding, please give me a call for a pro bono conversation.

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