What is Forensic Audio Authentication?

Forensic audio authentication is a form of forensic science used to determine if an evidence audio recording presents accurate information.  The evidence should be free from any alterations, deletions, additions, or applications of file manipulation.

File manipulation is the activity of altering analog or digital audio, images, and videos.  This can be done intentionally or unintentionally. Alterations that are done to a recording can change the meaning of events or information within a file.

The goal of audio forensic authentication is to provide an unbiased presentation following the best practices outlined by the Scientific Working Group for Digital Evidence (SWGDE) to establish that the evidence audio recording is consistent with how it was created.

Al Zlogar’s training allows him to use the tools and the latest approved scientific methods from the University of Colorado, Denver, Center for Media Forensics.  His goal is to apply the skills that he learned to help the legal community understand the integrity of an audio recording.

Al Zlogar Forensics also offers forensic audio enhancement services.

Authentication of Digital Audio Recordings

Authentication of digital audio recordings is a process that includes several steps outlined by the scientific community. I have incorporated these processes as best practices for Al Zlogar Forensics Inc. The available technology today allows an average person the ability to intentionally and unintentionally alter digital audio recordings. The goal of forensic audio authentication is to determine the integrity of a recording to be used as evidence in court.

Critical Listening

Al Zlogar begins all audio forensic authentication by critically listening to the audio evidence.  This allows him to document and note acoustic properties and events within a recording.  These would include background noise, voices, and any acoustic information that Mr. Zlogar will begin to test and measure after the initial critical listening stage.

File Analysis

Digital files are comprised of metadata and may include third-party software footprints that must be analyzed and documented.  The file analysis would include the format and metadata structure and provides critical information for the integrity of the evidence recording claimed by the party who produced the recording.

Time-Domain Analysis

After analyzing the file structure Al Zlogar begins to inspect and thoroughly document the time-domain information of a recording.  This entails noting any irregularities in the signal’s waveform, inspecting the power and energy information as well as noting the DC Offsets, and calculating the number of padded zeros at the beginning and end of the audio recording.

Frequency-Domain Analysis

The frequency-domain information of an audio signal is also analyzed and documented using software tools. iZotope RX and Adobe Audition provide excellent interactive modules that show important spectral information of an audio recording.

a visual representation of sound
iZotope RX’s Spectrogram

A Spectrogram is a unique visual representation of the audio signal’s frequency and amplitude over the time domain.  The Spectrum Analysis in the module is an interactive chart plotting the audio signal visually.

a visual representation of sound
iZotope RX

These frequency-domain visual forensic tools help to detect signal discontinuities, compression, originality, and signs of lossy compression artifacts.  This information is documented and used to verify the integrity of the evidence recording.

Creating an Exemplar

Exemplars are audio recordings created with the same methods used to create the evidence.  Reference audio files and exemplars are used to verify the integrity of the evidence by comparing the two for consistency.

Conclusion

A forensic scientist must remain unbiased at all times. It is best to begin any investigation on a need-to-know basis. It is of the utmost importance to use an ethical framework and to follow the principles outlined by the scientific community.

Contact our forensic audio expert to get an estimate for a quote.