Speech intelligibility at the perceptual boundary is titrated per subject by vocoding band count.

Evidence

To determine the number of frequency-bands to use, an offline intelligibility test was performed for each subject using a separate set of 40 speech snippets. The number of frequency-bands was chosen such that subjects could understand an average of two words in each snippet. — Dijk, Pim van, Physiology, Psychoacoustics and…, 4380