Mismatched distances from speakers to telephone in a forensic-voice-comparison case

•Illustration of methodology for implementing FVC based on conditions of a real case.•Use of relevant data, quantitative measurements, statistical models to calculate LRs.•Procedure for testing of validity and reliability under the conditions of the case.•Investigation of bias due to mismatched distances of speakers to the microphone.•Demonstration of three methods for mismatch compensation.

In a forensic-voice-comparison case, one speaker (A) was standing a short distance away from another speaker (B) who was talking on a mobile telephone. Later, speaker A moved closer to the telephone. Shortly thereafter, there was a section of speech where the identity of the speaker was in question – the prosecution claiming that it was speaker A and the defense claiming it was speaker B. All material for training a forensic-voice-comparison system could be extracted from this single recording, but there was a near-far mismatch: Training data for speaker A were mostly far, training data for speaker B were near, and the disputed speech was near. Based on the conditions of this case we demonstrate a methodology for handling forensic casework using relevant data, quantitative measurements, and statistical models to calculate likelihood ratios. A procedure is described for addressing the degree of validity and reliability of a forensic-voice-comparison system under such conditions. Using a set of development speakers we investigate the effect of mismatched distances to the microphone and demonstrate and assess three methods for compensation.