An audio forensic expert must investigate a recording used as evidence if one of the parties in litigation believes it has been edited or manipulated. Forensic audio authentication assists our clients in better understanding the information within their recorded audio evidence. So “how to authenticate an audio recording” is something our clients ask frequently. This page will help our clients understand the audio authentication investigations we can perform for litigation purposes.
In addition to determining if a recording has been tampered with, we can provide audio analysis services as well. Some examples include 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 , authentication is the process of substantiating that the asserted provenance of data is true. As defined in SWGDE Best Practices for Forensic Audio , an audio authentication examination seeks to determine if a recording is consistent with the manner in which it is alleged to have been produced.
HOW TO AUTHENTICATE AN AUDIO RECORDING
Our team of technicians and experts follow the best practices outlined by SWGDE and NIST when performing audio authentication analysis investigations.
US Department of Justice Special Report on Forensic Examination of Digital Evidence: A Guide for Law Enforcement 2004 Pg. 1
First, critical aural review of the submitted recording, without applying any processing, can yield information regarding areas to direct subsequent analyses. In addition to a preliminary overview, attention is paid to voices, acoustic events, background noise changes, uncharacteristic noises that may indicate equipment malfunction and possible record and edit events, as well as any other areas of specific interest.
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 that footprint in the metadata is observed and reported indicating the name of the software. Third party audio editing software like Adobe Audition or Sony Sound Force are capable of recording and editing.
Next, 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. The software that performs editing is highly sophisticated and can even change the sentence structure of dialogue.
Finally, 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.
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. A Spectrogram, or Fourier transform, as shown below, performs time/frequency domain testing.
Furthermore, the time/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. 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.
This is generally accomplished by a party involved in the events recorded or involved in the recording process affirming that the events heard during playback of the recording are consistent with that party’s recollection of the events as they transpired. When this is contested, a scientific analysis is conducted to test 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 any other digital media evidence investigator.
In conclusion, the forensic audio analysis investigations we perform include an unbiased and scientific analysis of every aspect evidence recordings. This not only ensures but guarantees an accurate and thorough forensic investigation.