Audio forensic evidence may come from a criminal investigation by law enforcement or as part of an official inquiry into an accident, fraud, accusation of slander, or some other civil incident.
The primary aspects of audio forensics are establishing the authenticity of audio evidence, performing enhancement of audio recordings to improve speech intelligibility and the audibility of low-level sounds, and interpreting and documenting sonic evidence, such as identifying talkers, transcribing dialog, and reconstructing crime or accident scenes and timelines. Once authenticity of the audio evidence is established, the forensic expert must rely on other techniques as well as their own expertise to determine the authenticity of the chain of custody, such as requesting the original.
If the original recording is on analog media, playback and duplication rely on physical processes that introduce noise and degrade the signal, even if slightly. A copy of an analog recording can never be an exact duplicate. An original digital recording is a bit stream from which the acoustic audio signal can be generated. Exact copies of that bit stream can be made. With digital evidence, each stage of copying can be exact, with no loss of quality between generations.
One of the most common audio issues that we address during an enhancement is noise and other extraneous “unwanted” sounds. The noise floor is usually consistent throughout the recording, and can be removed to varying degrees by using noise reduction software. The most complicated issues are the extraneous sounds that are not continuous. These sounds could include anything from a plane flying overhead to someone whistling while people talk. These sounds are difficult to pinpoint with standard tools such as noise reduction and equalization, but they can be identified using a spectrogram. After critical listening, the forensic expert must use electronic measurement to examine the audio evidence.
Digital audio recordings contain metadata which reveals information about how the recording was made, and the type of equipment that created the recording. If a recording was loaded into a software program capable of performing edits, there will often be a footprint left in the recording.
If you have a video that you question or need help understanding, please give us a call (312) 818-4788 for a pro bono conversation. Any and all formats of audio and video accepted. Retainer agreement available on request; travel expenses will be quoted in advance excluding meal expenses and flat rate time for travel instead of hourly.