Contribution
STIPA: Evaluating PA systems using the direct and indirect methods
* Presenting author
Abstract:
The IEC 60268-16 standard describes how to measure the Speech Transmission Index STI and STIPA (STI for public address systems), using two different measuring methods: the ‘direct method’, based on modulated noise, and the ‘indirect method’, based on impulse response measurements. DIRAC 7 features both methods, enabling an accurate comparative practical study. Measurements have been performed in four different university rooms, each equipped with a PA system (considered as black boxes). In this study, the level of two types of directly injected input signals, being an exponential sweep and modulated noise (standardized STIPA), have been set in 60 steps of 1 dB, from background noise level up to distortion level. At each step, the equivalent sound pressure level Leq, the signal to noise ratio SNR and the STIPA values have been measured. It is found that in the linear region, before dynamic compression starts affecting the signal, STIPA differences between the direct and indirect measuring methods are within the Just Noticeable Difference. From the compression threshold point, the direct method results in a decreasing STIPA value, while the STIPA value using the indirect method does not change until the clipping point is reached.