Enhancing Forensic Audio: What Works, What Doesn't, and Why

Abstract

'Enhancing' has become a routine part of preparing indistinct covert recordings for admission as evidence in criminal trials. Typically, evaluation of its effectiveness is seen as a simple matter of listening to determine whether the enhancement sounds ‘clearer’ than the original. This seems like a straightforward approach, but it brushes over many important issues which can adversely affect the fairness of the trial. This article outlines findings from experiments, case studies and scientific literature to show how enhancing can affect perception in surprising and unpredictable ways, without listeners’ conscious awareness. Discussion demonstrates that enhancing exacerbates, rather than mitigates, known risks of the jury being misled by an unreliable transcript. The conclusion indicates the direction in which to seek better procedures.