An Evaluation of Intrusive Instrumental Intelligibility Metrics

Instrumental intelligibility metrics are commonly used as an alternative to listening tests. This paper evaluates 12 monaural intrusive intelligibility metrics: SII, HEGP, CSII, HASPI, NCM, QSTI, STOI, ESTOI, MIKNN, SIMI, SIIB, and <inline-formula><tex-math notation="LaTeX">$\text{sEPSM}^\text{corr}$</tex-math></inline-formula>. In addition, this paper investigates the ability of intelligibility metrics to generalize to new types of distortions and analyzes why the top performing metrics have high performance. The intelligibility data were obtained from 11 listening tests described in the literature. The stimuli included Dutch, Danish, and English speech that was distorted by additive noise, reverberation, competing talkers, preprocessing enhancement, and postprocessing enhancement. SIIB and HASPI had the highest performance achieving a correlation with listening test scores on average of <inline-formula> <tex-math notation="LaTeX">$\bf \rho =0.92$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX"> $\bf \rho =0.89$</tex-math></inline-formula>, respectively. The high performance of SIIB may, in part, be the result of SIIBs developers having access to all the intelligibility data considered in the evaluation. The results show that intelligibility metrics tend to perform poorly on datasets that were not used during their development. By modifying the original implementations of SIIB and STOI, the advantage of reducing statistical dependencies between input features is demonstrated. Additionally, this paper presents a new version of SIIB called <inline-formula> <tex-math notation="LaTeX">$\text{SIIB}^\text{Gauss}$</tex-math></inline-formula>, which has similar performance to SIIB and HASPI, but takes less time to compute by two orders of magnitude.