How 'Enhanced' Forensic Audio is Evaluated in Criminal Trials: What if All That Really Gets Enhanced is the Credibility of a Misleading Transcript?

Covert recordings can provide powerful evidence in criminal trials. Since the audio is often of poor quality, many jurisdictions allow an ‘enhanced’ version to be admitted, along with a transcript, to assist the trier of fact in understanding the content of forensic audio. But how is ‘enhancing’ evaluated? In Australian courts, it is simply a matter for the jury to decide whether the processed audio ‘sounds clearer’ than the original. This paper presents two perception experiments showing, first, that ‘enhancing’ can make audio sound ‘clearer’ in the sense of ‘less noisy’ without making it objectively more intelligible; and, second, that ‘clearer’ audio makes listeners more likely to accept an unreliable transcript. This is a problem in view of common practices that result in admission of unreliable police transcripts as ‘assistance’ to juries. Discussion urges researchers to consider the legal context in which their work will be interpreted.