Impact on forensic voice comparison of speech acquired from the GSM mobile phone network – some preliminary results

Before the development of mobile phones, intercepted speech was often recorded from the landline phone network and was used by the forensic scientist in Forensic Voice Comparison (FVC) for evaluating the strength of evidence between suspect and offender data. Nowadays, mobile phones are much more widely used compared to landline phones particularly by the criminal fraternity. One of the common misconceptions among forensic scientists is that technologically the landline and mobile phone networks are the same, which leads them to assume the impact of these technologies on speech parameters will be the same. But this is very far from the truth [1]. There exist two common network topologies for mobile phone systems: Global System for Mobile Communication (GSM) and Code Division Multiple Access (CDMA). This study will focus on the impact of one of the mobile phone network topologies, namely the GSM network, on speech parameters that are important to FVC. The GSM mobile phone network incorporates a GSM AMR speech codec whose primary function is to compress the speech signal into a low bit rate stream to account for the set of channel conditions existing during a single call. It needs to be emphasized that the codec is solely responsible for the quality of the transmitted speech under all the possible operating modes of the GSM network. Therefore the impact of the GSM network on speech parameters needs to be investigated by analysing speech befor