The effect of amplitude compression on wide band telephone speech for hearing-impaired elderly people

Recently, high-speed multimedia communication systems have become widespread. Not only conventional narrow band speech signal (up to 3.4 kHz) but also wide band speech signal (up to 7 kHz) can be transmitted through high-speed communication lines. Generally, the quality of wide band speech signal is high and its articulation score is good for normal-hearing people, but for elderly people who have hearing losses in higher frequencies, the effect of wide band speech is doubtful. Therefore, we investigated the effect of wide band phone speech on the elderly people’s speech perception in terms of articulation. And we also considered the effect of amplitude compression method that is used for hearing aids. Japanese 62 CV syllables were used as test speech samples. The original speech samples were re-sampled to narrow band speech (8 kHz sampling) and wide band speech (16 kHz sampling). All speech samples were processed with AMRCODEC (Adaptive Multi Rate COder-DECoder), which is a voice coding system available to both narrow band and wide band speech signals. Then, coded speech signals were processed with a multi-band amplitude compression method. Ratios of the compression in each frequency bands were determined according to the average value of subjects’ hearing levels. All subjects were native Japanese speakers, aged 68 to 72 years, and have hearing losses (more than 40 dB HL). From the results of the test, we found that combination of wide band speech and amplitude compression showed significant improvement of the articulation.