Some common error mechanisms in making STI intelligibility measurements

STI and its derivatives (RaSTI and STIPa) have become the internationally accepted methods for acoustically measuring the potential intelligibility performance of both sound systems and rooms. Their use has unquestionably brought about a significant improvement in public address/voice alarm system quality and intelligibility. However, in practice, many of the measurements made on site may be unwittingly based on flawed techniques. The paper examines a number of common problems found to affect measurement accuracy. Significant differences between different measurement platforms and techniques are reported. Furthermore, different stimulus formats and even their recording and playback medium are also shown to potentially affect the final result. It is shown that neither STI nor STIPa, in their current formats, accurately predicts the intelligibility of sound systems with irregular frequency responses, particularly when these are operating in reverberant, high signal‐to‐noise environments, a common effect fou...