Discriminability of the quality of amplitude-compressed speech

In an earlier experiment on intelligibility of amplitude-compressed speech, subjects could not hear a difference between noncompressed speech and speech under some conditions of compression. Therefore, compression conditions were determined in which the quality of the two types of speech could be distinguished. When speech average level was 10 dB above a masking noise, compression ratio (CR) was equal to 2.5, and the attack time (Ta) was 3 ms, the release time (Tr) had to be shorter than 120 ms to achieve discrimination by trained normal-hearing subjects. With longer attack times and/or higher compression ratios, the critical value of release times increased. Thus, the range in which the discrimination was observed also increased (for CR = 5 and Ta = 10 ms, the critical Tr was 360 ms). The discrimination of our hearing-impaired subjects was much worse than that of the normal-hearing subjects. For example, speech processed with CR = 10, Ta = 1 ms, and Tr = 10 ms could be distinguished from the noncompressed by only 50% of the impaired subjects.