Practical Limitations of Objective Speech Intelligibility Measurements of Sound Reinforcement Systems
The paper examines the most commonly used acoustically based speech intelligibility measures, such as %ALcons and STI and Rasti, as well as the lesser used early-energy fractions such as C7 and C50, and highlights their uses and more particularly their limitations. Common error mechanisms are discussed, together with the effects of nonlinear electronic and acoustic environments. The erroneous effects that can be caused by modern signal processing and ways of avoiding such problems are also presented. The inability of such measures to take into account other factors, such as distortion, equalization and source coherence, are also raised, and the implication for producing workable standards of measurements is discussed.
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