Intelligibility assessment in forensic applications

In the context of forensic phonetics the transcription of intercepted signals is particularly important. However, these signals are often degraded and the transcript may not reflect what was actually pronounced. In the absence of the original signal, the only way to see the level of accuracy that can be obtained in the transcription of poor recordings is to develop an objective methodology for intelligibility measurements. This study has been carried out on a corpus specially built to simulate the real conditions of forensic signals. With reference to this corpus a measurement system of intelligibility based on STI (Speech Transmission Index) has been evaluated so as to assess its performance. The result of the experiment shows a high correlation between objective measurements and subjective evaluations. Therefore it is recommended to use the proposed methodology in order to establish whether a given intercepted signal can be transcribed with sufficient reliability.