Effects of dividing frequency in filtering for dichotic presentation to reduce masking to a consonant by the preceding vowel

Intelligibility tests were performed using the first three vowels /a/, /i/, and /u/ in nonsense vowel/u/-consonant-vowel (VCV) syllables to examine the relationship between the effective dividing frequency and the difference of preceding vowels. The listening test was conducted in a soundproof room and speech stimuli were presented to listeners through headphones. The speech signal was split into two bands using a low-pass filter (LPF) and a high-pass filter (HPF) for a dichotic condition. The speech signal level was maintained at the listener's most comfortable level (MCL), which was determined under the dichotic condition. The intelligibility scores obtained under the dichotic 0.8 and dichotic 1.0 conditions were higher than that obtained under the diotic-6dB condition. The result of speech intelligibility tests show that a two-band dichotic presentation with a dividing frequency higher than 1.6 kHz is not effective in intelligibility for hearing-impaired listeners.