Audio forensics is concerned with scientifically representing, analyzing and evaluating audio recordings obtained from a criminal or a civil legal proceeding. Recordings that have been analyzed and evaluated by an audio forensic can be presented as physical evidence in court or other official venues. The authenticity of any audio evidence must be verified before it is presented in court. If this is not done, the evidence will be deemed inadmissible.
This is where audio forensic services come into play. These services are provided by trained and experienced audio forensic examiners. The examiner is an expert who plays a crucial role in determining whether or not an audio recording is authentic. After analyzing the recording, the audio forensic examiner can interpret whether the recording is original or not or whether it has been tampered with.
Techniques of Analysis
Different audio forensic techniques can be used to authenticate the integrity of an audio recording or other digital evidence. These techniques have been developed to detect any tampering with the audio evidence. Audio verification techniques can be divided into two main types:
- Container-based Authentication: This includes the file structure and the audio file’s metadata and description.
- Hash-based Analysis: The hash value is fixed numeric, and two files cannot have the same value. If an audio forensic examiner detects any change in the hash value of the same file, it indicates that modifications have been made to the file.
- MAC Time Stamps: This detects the date and time that the file was created and modified.
- File Format: A brief description of the audio file is stored for future reference, complete with all relevant information.
- Header: Using any header information and hexadecimal reader of the file can help detect any modification made to it. An authentic file will have a matching file name and file name extension.
- Hex Data: The file’s raw digital data may have different useful information such as external software titles (if they are present), audio block addresses and post-processing operations.
- Content-based Authentication: This analysis includes the audio file’s actual bits and bytes.
- Electronic Network Frequency (ENF): This process depends on the ENF traces present in the audio. Examiners can visually identify that the file has been tampered with through abrupt changes in the spectrogram’s power grid signal.
- Time Frequency: Other signals are also recorded by the recording device. These signals include signatures that provide information regarding the recording location and file ownership.
- Enhancement: Audio forensic examiners perform audio enhancement by removing unwanted noise in the recording and improving speech quality.
- Environment: Examiners use Acoustic Environment Identification (AEI) for audio authentication and real-time identification of a crime. You can calculate AEI by estimating background noise and reverberation.
- Compression: Some people compress and decompress audio files for malicious reasons. Audio forensic experts recompress it at a higher bit to make it a high-quality audio file.
Beneficial to law
Audio forensic services serve many purposes and are particularly beneficial to law enforcement. Everyone is familiar with the techniques used to modify audio recordings in this digital day and age. With the help of audio forensics, investigators can find out the truth and bring the guilty to justice.
