- linear peak clipper (PC) amplifies input sounds linearly up to its maximum output capabilities, such that when input sounds go up by 10 dB, so do output sounds;
- compression limiter (CL) amplifies input sounds linearly up to a predetermined level, however after a certain point, the output is reduced automatically by a fixed ratio; and
- wide dynamic range compressor (WDRC) allows input signals that vary in level over a wide range to be amplified as a narrower range of output signals.
Researchers found that all three types of hearing aid circuits:
- Improved speech recognition of one-syllable words by an average of 29 percent;
- Improved recognition of connected speech by 10 to 30 percent in noise and greater improvements for speech at soft and conversational levels;
- Improved quality of speech for soft and conversational speech levels (and did not significantly degrade the overall quality of listening for loud speech); and
- Significantly reduced the frequency of problems encountered in verbal communication.
The major finding was that each of the three circuits provided significant benefit both in quiet and in noise. The differences among the circuits were small compared with benefits. For example, the CL and the WDRC provided slightly more benefit in some situations than PC circuits. Participants rated the CL circuit as most preferred.
The clinical trial was a comprehensive federal collaboration between the NIDCD and the Department of Veterans Affairs Cooperative Studies Program. NIDCD supports and conducts research and research training on normal and disordered processes of hearing, balance, smell, taste, voice, speech and language and develops and disseminates health information based on scientific discovery. The Department of Veterans Affairs provides medical care to America's veterans and conducts research programs on a wide array of medical issues.
To schedule an interview with NIDCD staff or to learn more about the study, hearing aids or sensorineural hearing loss, please contact the NIDCD Office of Health Communication and Public Liaison at (301) 496-7243 and visit their Web site at: www.nih.gov/nidcd.