Recent years have seen a great deal of attention given to the reliability of expert evidence admitted in criminal trials. However, almost no attention has been given to the reliability of evidence provided by so-called ‘ad hoc experts’. Indeed, many forensic scientists seem unaware that such a category of witness even exists, much less of the substantial threats they pose to the fairness of our criminal justice system. ‘Ad hoc experts’ are used for a number of evidence types. Here, we concentrate on one type that appears in Australian courts on a weekly basis: interpretation of indistinct covert recordings. The aim is to draw the attention of AJFS readers to serious problems in the handling of this much-used form of evidence, in the hope that the AAFS might develop a position on the issues and support calls for reform of practice.