Comments on "compression? Yes, but for low or high frequencies, for low or high intensities, and with what response times?" Dillon, H. (1996), Ear and Hearing, 17, 287-307.

Harvey Dillon discusses the effect of compression on understanding speech in noise in terms of the effect on the signal to noise ratio. The most common noise with which hearing-impaired persons must contend is competing speech, and the only practical computer smart enough to separate such interference from the target speech is the human brain, using its capacity for "selective listening." Hearing aids with full-dynamic-range compression and frequency-response shaping, by restoring redundant speech cues that the hearing-impaired person no longer hears because of recruitment and high-frequency loss, can empower the user's ability to listen selectively, at the expense of degrading the signal to noise ratio under some conditions.

A Different Approach to the Noise Problem of the Hearing Impaired.

Hearing aid design to alleviate the noise problem has concentrated on improving the signal-to-noise ratio with the aid, using devices such as directional microphones, adaptive filters, and circuits that discriminate between steady-state noise and speech. The design approach discussed here is directed at improving the speech recognition of hearing-impaired listeners at a given signal-to-noise ratio, by restoring to their perception speech cues they no longer hear because of their impairment. This allows them to retain more of the redundant information in speech after masking has taken its toll, and empowers their ability to separate desired from undesired signals (what Broadbent calls "selective listening" in persons with normal hearing). Experimental results are presented.

Comments on "Earphones in Audiometry" [Zwislocki et al., J. Acoust. Soc. Am. 83, 1688-1689 (1988)].

The Zwislocki et al. ["Earphones in Audiometry," J. Acoust. Soc. Am. 83, 1688-1689 (1988)] Letter to the Editor states that insert earphones have some unresolved technical problems, such as limited frequency response, limited dynamic range and power handling capability, intersubject variability, and hygiene safety. In evaluating circumaural earphones, Zwislocki et al. say that the lack of a standard coupler disqualifies them for audiometry. Since this letter carries the weight of a CHABA committee recommendation, these issues are commented on herein. Section I was written primarily by Mead Killion and Sec. II primarily by Edgar Villchur. For brevity throughout, the authors of the Zwislocki et al. letter will be referred to as "the authors."

Multichannel compression processing for profound deafness.

Three-channel amplitude compression followed by frequency shaping was used to process test sentences for five profoundly deaf subjects, and the recognition scores were compared to scores achieved with frequency shaping only. At preferred levels, the scores of three of the five subjects showed a statistically significant but not dramatic advantage for compression; the averages of the scores for these three subjects were 29.2 percent for the uncompressed speech and 39.5 percent for the compressed speech. The preferred-level scores of the other two subjects did not show a statistically significant advantage for compression; averages were 33.7 percent for uncompressed speech and 36.1 percent for compressed speech. Tests at input levels 10 dB and 15 dB below preferred levels were also given to four of the subjects (the fifth had to leave the experiment early). In the reduced-level tests all four subjects showed a statistically significant advantage for compression. The averages of reduced-level uncompressed scores for the four subjects were 10.7 percent and 15.2 percent at -15 dB and -10 dB levels, compared to compressed scores at these levels of 31.7 percent and 32.5 percent. When visual cues were added to the auditory presentation in an exploratory experiment with one subject, the benefit of compression carried over into the higher scores.