Digital forensic analysis of audio recordings

Today, digital audio recordings are increasingly used as evidence to support or refute relevant facts in legal proceedings. Their submission as evidence may require an assessment of their origin, authenticity and integrity, particularly when questions arise regarding how they were obtained, preserved or submitted.

However, simply listening to a recording or submitting a transcript does not make it possible to determine whether the file corresponds to the original recording or whether its integrity has been preserved. A digital audio file may have been copied, converted to another format, trimmed, assembled from different fragments, or generated or manipulated using artificial intelligence. It may therefore be necessary to examine the file, the source device and the audio signal itself in order to assess its reliability.

What do we analyse in a forensic examination of digital audio recordings?

• Preservation and chain of custody: acquisition and preservation of the digital recording using procedures that make it possible to demonstrate its integrity and document the actions carried out during the examination.
• Origin, authenticity and integrity of the recording: examination of the file and the device concerned to assess its origin, determine whether it is the original recording or a copy, and identify possible signs of cuts, insertions, edits or other alterations.
• Metadata and technical structure analysis: examination of dates, duration, format, codec, sampling rate, number of channels, software used and any other technical information available within the file.
• Audio signal analysis: examination of the waveform, spectrogram, frequency spectrum and other parameters to locate discontinuities, abrupt acoustic changes, repeated fragments, re-encoding and possible editing processes.
• Detection of synthetic voices and AI-generated audio: assessment of technical indicators consistent with synthetic voice generation, voice cloning or artificial intelligence manipulation through the combined examination of the file, its metadata, the audio signal, possible acoustic artefacts and specialised detection tools.
• Voice and acoustic context analysis: assessment of the number of voices present, when each person speaks, non-vocal sounds, background noise and changes in the acoustic environment recorded in the audio.
• Intelligibility enhancement and transcription: processing of working copies to improve the understanding of voices or difficult-to-hear fragments, while always preserving the original file, and preparation of a transcript when required.
• Independent expert review of audio recordings: technical review of the audio files and expert reports submitted by the opposing party to determine whether their conclusions are supported by the files examined and the methodology applied.