Information-bearing components of speech intelligibility under babble-noise and bandlimiting distortions

Performance of speech technologies can benefit greatly from a deeper appreciation of the nature of the information- bearing features in continuous speech. To explore these features, we focus here on the role of the spectral and temporal modulations in maintaining the intelligibility of speech as it becomes severely degraded by low-pass filtering and additive babble noise. These modulations are estimated using a biological model of auditory processing which approximates the representation of sound in the cortex. Intelligibility of the noisy speech is computed directly from this model via the spectro-temporal modulation index (STMI), and the validity of this metric is confirmed by a detailed comparison with results of psychoacoustic tests. Our analysis reveals quantitatively why certain types of noise are more disruptive to speech intelligibility than others (e.g., babble vs. white noise). It also highlights the important contribution of both spectral and temporal modulations in accurately predicting the intelligibility of speech under adverse conditions.