scope:

The predictions of this Standard apply to listening conditions where the input variables of the Speech Intelligibility Index (Sll) model can be accurately estimated. The input variables include the equivalent speech spectrum level, the equivalent noise spectrum level, and the equivalent hearing threshold level. This includes the conditions where either speech or noise may not exist as directly measurable physical quantities (e.g., conditions where speech correlated noise is present, such as rever-berated speech) but where equivalent speech spectrum level, equivalent noise spectrum level, and equivalent hearing threshold level can. never-theless. be calculated. The predictions made by use of this Standard are correct only on the average. that is, across a group of talkers and a group of listeners of both genders. The scope of the Standard is limited to natural speech, otologically normal listeners, and communication conditions which do not include multiple, sharply filtered bands of speech or sharply filtered noise. In addition, the listeners should have no linguistic or cognitive deficiencies with respect to the language used.