Problems of Forensic Sciences 2017 Vol. 109 (CIX) 27-42
PROPERTIES OF RECORDINGS AND AUDIO FILES SAVED IN AMR FORMAT AND AN ASSESSMENT OF THE POSSIBILITY OF APPLYING THEM IN AUTHENTICITY EXAMINATIONS
Marcin MICHAŁEK
Institute of Forensic Research, Kraków, Poland
Streszczenie
One of the commonly used formats for recording audio on mobile devices is Adaptive Multi-Rate (AMR). It was primarily designed to transmit and store speech, although it can also be used to record other acoustic signals. AMR file format is mainly used for recording audio on mobile phones with a voice recorder function. It can also be used for storing so-called voice messages, offered as a service by mobile telephony operators. Recordings originating from mobile phone memories, including in AMR format, are currently a significant part of all analysed evidence recordings. That is why it is important to analyse the authenticity of AMR audio recordings. The purpose of this work was to analyse recordings and audio files stored in AMR file format and to study their application in authenticity examinations. Another goal was to create our own software to automatically analyse the file structure of such recordings. The study was based on AMR audio recordings which were made using different brands and models of mobile phones. The obtained results allowed us to establish that recording in the seemingly uncomplicated AMR file format enables the authenticity of such recordings to be investigated. It is also possible to use well-known methods such as the Electrical Network Criterion and file properties and structure in such investigations. An algorithm and software for the automatic analysis of the integrity of AMR audio files in the MATLAB computing environment were also developed.
Słowa kluczowe
AMR; Authenticity analysis; Digital recording; File structure.