On the combined effects of signal-to-noise ratio and room acoustics on speech intelligibility.

Speech intelligibility in rooms is influenced by room acoustics effects and by the signal-to-noise ratio (S/N) of the speech and ambient noise. Several measures such as useful-to-detrimental sound ratios and the speech transmission index predict the combined effects of both types of factors. These measures were evaluated relative to speech intelligibility test results obtained in simulated sound fields. The use of simulated sound fields made it possible to create the full range of combinations of room acoustics and S/N effects likely to be found in rooms for speech. The S/N aspect is shown to be much more important than room acoustics effects and new broadband useful-to-detrimental ratios were validated. Useful-to-detrimental ratios, speech transmission index measures, and values of the articulation loss for consonants were all reasonably accurate predictors of speech intelligibility. Further improvements to these combined measures are suggested.