Effect of Noise and Filtering on Speech Intelligibility at High Levels
Irwin W. Pollack, J. M. Pickett · The Journal of the Acoustical Society of America · 1957
The effects of high sound levels on wide-band speech in noise roughly parallel the effects of high levels on filtered speech. The Articulation Index (AI) concept encompasses both findings if it is assumed that the effect of high sound levels is to produce an effective change in AI.