We report our ongoing efforts towards the development of challenging speaker discrimination tests. Our goal is to establish highly sensitive tests that enable characterization of individual differences in voice processing skills. Such tools are required but lacking for the identification of so-called “voice super-recognizers” (VSR) – individuals with superior ability, who could aid criminal investigations involving audio material. We manipulated test difficulty by implementing a new ASR and delta F0- based stimuli selection method. Independent groups of (police cadet) participants performed 2-alternative forced choice voice discrimination test of stimulus pairs selected either randomly, or systematically based on inter-item similarity. On average performance was significantly higher for the prior (79.1%) as compared to the latter (68.8%) test. Thus, we have now established a method to manipulate task difficulty in speaker discrimination. We will further validate and extend our method to include a wider range of audio material implemented as a within- subject design.