Effect of covert recordings from vehicles on the performance of forensic automatic speaker recognition


  • Hermann J. Künzel University of Marburg




automatic forensic speaker recognition, covert recordings, telephone transmission


Speech recordings made in vehicles with hidden recording devices (“bugs”) present a number of peculiarities compared to high-quality direct microphone recordings, and also ordinary mobile phone recordings. Inspired by a recent court case the present investigation was undertaken to quantitatively assess the effect of three types of covert recordings, including data transmission, on a widely-used forensic automatic speaker recognition (FASR) system (Batvox 3.1). Using simultaneous high-quality re-recording of speech samples from 50 speakers played back inside four automobiles and one 5-ton RV as a benchmark, equal-error rates (EERs) between zero and 2 % were found. The latter number was obtained for GSM-transmitted voice data. When the acoustic data were not transmitted but stored inside the covert recording device, or recorded and stored on a smartphone placed inside the vehicles, EERs between zero to 0.45 % were obtained. Generally, EERs are similar to those obtained using the same FASR system in studies with non-covert recordings (direct recordings, landline and mobile telephone). No effect of the type or model of the vehicles on EERs was observed.

Author Biography

  • Hermann J. Künzel, University of Marburg
    Hermann J. Künzel was Professor of Phonetics at the University of Marburg, Germany, from 1999 to 2015, and Head of the Speaker Identification & Tape Authentication Department of the Federal Criminal Police Office (BKA) in Wiesbaden, Germany from 1985 - 1999. In the latter position he was essential in the development of the acoustic-phonetic method of forensic speaker recognition (FSR). Künzel has been, and still is, working as a professional expert in FSR, speaker profiling, voice line-ups and non-speech related acoustic investigations (e.g. aircraft and ship mishaps) for courts and government institutions throughout Germany and worldwide. He has been applying automatic speaker recognition (AFSR) to cases of lawful interception (LI) and in Court since 2001.






How to Cite

Künzel, H. J. (2017). Effect of covert recordings from vehicles on the performance of forensic automatic speaker recognition. International Journal of Speech, Language and the Law, 24(1), 31-44. https://doi.org/10.1558/ijsll.30985