The Hearing-Aid Speech Perception Index (HASPI)

• We propose a new intelligibility index based on the outputs of an auditory model.
• The auditory model incorporates peripheral hearing loss and is accurate for both normal and impaired hearing.
• The index compares the model outputs for a processed signal with the outputs for an unprocessed reference signal.
• The index combines measurements of envelope and temporal fine structure fidelity.
• Index results are presented for noise, distortion, and nonlinear signal processing outputs.

This paper presents a new index for predicting speech intelligibility for normal-hearing and hearing-impaired listeners. The Hearing-Aid Speech Perception Index (HASPI) is based on a model of the auditory periphery that incorporates changes due to hearing loss. The index compares the envelope and temporal fine structure outputs of the auditory model for a reference signal to the outputs of the model for the signal under test. The auditory model for the reference signal is set for normal hearing, while the model for the test signal incorporates the peripheral hearing loss. The new index is compared to indices based on measuring the coherence between the reference and test signals and based on measuring the envelope correlation between the two signals. HASPI is found to give accurate intelligibility predictions for a wide range of signal degradations including speech degraded by noise and nonlinear distortion, speech processed using frequency compression, noisy speech processed through a noise-suppression algorithm, and speech where the high frequencies are replaced by the output of a noise vocoder. The coherence and envelope metrics used for comparison give poor performance for at least one of these test conditions.