Impact of mobile phone usage on speech spectral features: some preliminary findings

Abstract

The manner of using a mobile phone in voice communications can significantly affect the spectral characteristics of the speech signal. This article presents preliminary results of the analysis of the long-term average speech spectrum (LTASS), the long-term formant distribution (LTF) in voiced sounds, and vowel formants F1, F2 and F3 of six speakers in five modes of mobile phone usage. These modes are: normal holding of a mobile phone (NOR), with a bonbon (sweet) in the mouth (BON), with a cigarette between the lips (CIG), with the mobile phone between cheek and shoulder (SHO) and with the hand covering the mobile phone and mouth (HAN). The results show that each mode has an impact on spectral features and that the modes HAN and SHO have the greatest impact. The most striking results are the relative displacement of F1, which can reach 30% (e.g. vowel /a/ in HAN mode for males), formant F2, near 15% (vowel /i/ in SHO mode for males), and formant F3, about 5% (vowel /u/ in CIG mode for females). These findings suggest that forensic practitioners should exercise caution in interpreting formant measurements in speaker identification cases involving mobile phone transmission.