Investigations of the just-noticeable-difference of clarity index (C80)

The clarity index for music (C80) is a valuable room acoustic parameter, as it is an objective measure of how listeners perceive clarity. Knowing the just noticeable difference (JND) of C80 is of great importance to concert hall designers. Limited previous research has been conducted to find the C80 JND, and the major studies have limitations, including a small sample size. The reported JND is approximately 1 dB. An ongoing investigation is being conducted at the University of Hartford to establish the validity of these results by experimentally determining the JND, including an investigation on test method. In the first study (Ahearn etal., 2009), the subject pool was increased to 51 subjects, using test methods from prior research. The next study (Giacomoni etal., 2010) compared two C80 JND test methods, including allowing subjects to switch between signals in real-time. The results revealed the importance of subject training. In the third study (Wells etal., 2010), the switch method was used. The resulting JNDs were 1.6, 3.8, and 4.0 dB for each of the studies, respectively, showing that the C80 JND may be significantly higher than previously thought. The testing methods, results, and comparison to the previous studies will be described.