Measuring methods of the intelligibility and the intelligibility limit of voice signals

The definitions of the voice signal intelligibility and the intelligibility limit are discussed, and the methods to measure intelligibility are examined. While intelligibility is defined as a percentage, the corresponding limit is defined as the perturbation condition for which intelligibility is reduced to 50%, expressed as signal level or signal to noise ratios. The measuring method varies with the type of phoneme used (meaningless phrases, rhymed works, or normal speech). Intelligibility curves for the three methods are given.