Transformation of voice onset time in hearing aid processed speech and its relation with number of channels in hearing aids

Abstract

Modification of temporal features of a speech signal as it passes through the processing stages in a digital hearing aid may affect the speech recognition and speech perception. Transformation of voice onset time (VOT) may be one factor which affects the intelligibility of hearing aid processed speech and thereby affecting the factor of clarity of sound. The contribution of VOT transformation in the degradation in speech quality with increase in the number of channels of a hearing aid needs to be investigated. The objectives of the study are 1) to acoustically analyze and extract VOT from the speech signal at the input and output of a 2, 4, 6 and 16 channel digital hearing aid, 2) to estimate the transformation of VOT in a 2, 4, 6 and 16 channel hearing aid processed speech and 3) to investigate the effect of number of channels of hearing aids on this transformation. The stimulus consisted of three meaningful voices cognate word pairs, such as BEES / PEAS, DIME / TIME and GOAT / COAT produced by a male adult (native Kannada) speaker. VOT values were found out for the UN processed stimuli and for the processed stimuli from four behind the Ear hearing aids, by using speech analysis software and then the corresponding changes in VOT was noted. Perceptual evaluation was done by six judges with normal hearing. Results showed a reduction in lead VOT by 16% in hearing aid processed speech which would result in degradation of speech intelligibility by about 11% and a reduction in lag VOT by 18.4% leading to a decrease in percentage intelligibility by 19.4%. No significant difference between the percentage reduction in lag VOT and lead VOT was observed across processed speech of hearing aids with different channels