Articulation index: Importance function in the intensity domain
Arthur Boothroyd · The Journal of the Acoustical Society of America · 1990
In the classical derivation of the articulation index (AI) account is taken of the relative contributions of different parts of the acoustic spectrum in the frequency domain, as represented by the importance function. In the intensity domain, however, it is assumed that there is a constant contribution per decibel over a range of 30 dB. In fact, the intensity domain can be treated like the frequency domain, assigning different weights to different parts of the intensity distribution. Moreover, by integrating the logarithm of the error probability over intensity, it is possible to predict the shape of the performance/intensity (PI) function that relates recognition probability to signal-to-noise ratio. Under the assumption of a quasi-Gaussian importance function in the intensity domain, predicted PI functions are very similar to those obtained experimentally. Modifications to the parameters of the importance function permit modeling of some of the effects of changes of vocal effort, talker distance, and sensorineural hearing loss.