FORENSIC AUDIO AUTHENTICATION
AND AUDIO ANALYSIS
An audio forensic expert must investigate a recording used as evidence if one of the parties in litigation believes editing or manipulation occurred. Forensic audio authentication and audio analysis assists our clients in better understanding the information within their recorded audio evidence. So our clients frequently ask how to authenticate an audio recording.
Furthermore, this page will help our clients understand the audio authentication investigations we perform for litigation purposes.
In addition to determining if a recording has been tampered with, we provide audio analysis services. For example, we conduct comparative analysis between two audio files, SPL (sound pressure level) testing and timing of sounds like gunshots.
WHAT IS AUDIO AUTHENTICATION?
Similarly, as defined in [1], authentication is the process of substantiating that the asserted provenance of data is true. As defined in SWGDE Best Practices for Forensic Audio [2], an audio authentication examination seeks to determine if a recording is consistent with the manner in which it is allegedly produced.
HOW TO AUTHENTICATE AN AUDIO RECORDING
Our team follows the best practices outlined by SWGDE and NIST when performing audio authentication analysis investigations.
ASSESSMENT
Audio forensic examiners should assess digital evidence thoroughly with respect to the scope of the case to determine the course of action to take.
ACQUISITION
Digital evidence, by its very nature, is fragile and easily altered, damaged, or destroyed. Alterations are mostly due to manipulation or improper handling or examination.
EXAMINATION
The examination process extracts and analyzes digital evidence. Extraction refers to the recovery of data from its media.
DOCUMENTING AND REPORTING
The expert documents his/her actions and observations throughout the forensic processing of evidence. This concludes with the preparation of a written report of the findings.
US Department of Justice Special Report on Forensic Examination of Digital Evidence: A Guide for Law Enforcement 2004 Pg. 1
INTEGRITY TESTING
CRITICAL LISTENING
First, critical aural review of the submitted recording, without applying any processing, yields information regarding areas to direct subsequent analyses. In addition to a preliminary overview, we observe voices, acoustic events, background noise changes, uncharacteristic noises that indicate equipment malfunction and possible record and edit events, and any other areas of specific interest.
METADATA ANALYSIS
Second, 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 identifiable, then the reported metadata footprint indicates the name of the software. Third party audio editing software like Adobe Audition or Sony Sound Force are capable of recording and editing.
EDITING DETECTION
Third, audio evidence is inadmissible in a court of law if it evidence of alteration is detectable. There are many methods to which you can alter audio recorded evidence. A user can edit a recording to remove relevant information. They can also edit a recording to include irrelevant information. In fact, highly sophisticated editing software can even change the sentence structure of dialogue.
EXEMPLAR CREATION
Finally, when examining the digital information, we must create an exemplar recording to compare the metadata with the original. An exemplar is a recording made in conditions that are as close to the original recording as possible. Using this exemplar, the forensic expert can compare the metadata and HEX information of the two files.
TIME/FREQUENCY DOMAIN TESTING
The formatting of digital audio recordings are easily manipulated with malicious and accidental intent. The characteristics of an audio recorder, such as sampling rate or start signature, capture audio signals in a specific way. These characteristics are detectable through electronic measurement testing in visual representation. These tests display either consistencies or inconsistencies with what we would expect to see from an original, unaltered audio recording.
Furthermore, the time and frequency domain testing we perform notes the prominent frequencies in the voices or other sound source and the noise floor. If the frequency range of a voice suddenly expands shifts, this can be a sign of an edit. In addition, sudden changes in the noise floor presence/level are indications or evidence of editing.
AUDIO AUTHENTICATION IN COURT
The term “authentication” in a legal context describes the establishment of a proper legal foundation for the admission of a recording as evidence into a judicial proceeding.
During playback, a party involved in the events affirms consistency between the recording and their recollection. When contested, scientific analysis then tests any disputed claims.
We understand the weight our conclusions as an expert witness may have in a litigation. Therefore, we have an attention to detail for every forensic audio analysis investigation unlike other digital media evidence investigators.
In conclusion, our forensic audio analysis investigations include an unbiased and scientific analysis of every aspect evidence recordings. This not only ensures, but guarantees, an accurate and thorough forensic investigation.
