‘Enhancing’ forensic audio: false beliefs and their effect in criminal trials

Indistinct covert recordings admitted as evidence in criminal trials are routinely ‘enhanced’ to assist a jury in making out their contents. But just what is ‘enhancing’, and how effective is it? This paper uses two short experiments to demonstrate that a subjective impression that ‘enhancing’ has made the audio ‘clearer’ does not necessarily indicate there has been an objective improvement in intelligibility. It then outlines, in a non-technical manner, the capabilities and limitations of various ‘enhancing’ techniques, and discusses implications in relation to current legal practices around the admission and use of ‘enhanced’ audio in Australian criminal trials. Finally, it recommends that ‘enhanced’ versions of forensic recordings should only be admitted on the basis of objective evidence of the extent to which they have genuinely improved the intelligibility of the specific audio being used, noting that such evidence is easy to obtain and provide.