Speech based transmission index for all: An intelligibility metric for variable hearing ability.

A method to measure the speech intelligibility in public address systems for normal hearing and hearing impaired persons is presented. The proposed metric is an extension of the speech based Speech Transmission Index to account for accurate perceptual masking and variable hearing ability: The sound excitation pattern generated at the ear is accurately computed using an auditory filter model, and its shapes depend on frequency, sound level, and hearing impairment. This extension yields a better prediction of the intensity of auditory masking which is used to rectify the modulation transfer function and thus to objectively assess the speech intelligibility experienced by hearing impaired as well as by normal hearing persons in public spaces. The proposed metric was developed within the framework of the European Active and Assisted Living research program, and was labeled "SB-STI for All." Extensive subjective in-Lab and in vivo tests have been conducted and the proposed metric proved to have a good correlation with subjective intelligibility scores.