Relationship between intelligibility, naturalness, and listening effort of source-separated speech

Various signal processing techniques have been proposed for separating a speech signal from an acoustic environment that includes other sound sources. One important measure of success of a source separation method is the intelligibility of the extracted speech signal, determined as the fraction of intended words correctly recognized. However, even when speech samples have similar intelligibility, they may differ in the degree of cognitive effort required to understand them, or in the degree to which they sound pleasant or natural to a listener. We present results of an experiment in which listeners heard context-free stimuli recorded in a noisy environment by two different talkers, and subsequently processed in various ways to enhance the speech and suppress the noise. Listeners first transcribed and then judged the “naturalness” and “listening effort” of the speech. Intentionally, stimulus intelligibility varied widely—as did naturalness and effort. We present and discuss the measured relationship among intelligibility, perceived naturalness, and reported listening effort.