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Processing the telephone speech signal for the hearing impaired
1Department of Communication Disorders and Speech Science, University of Colorado, Boulder.
Ear and Hearing
|April 1, 1992
Summary
Digital signal processing significantly improves speech intelligibility for individuals with sensorineural hearing loss. Techniques like frequency and time domain processing enhanced understanding, with a preference for emphasis-based signals in telephone applications.
Area of Science:
- Audiology
- Signal Processing
- Speech Communication
Background:
- Sensorineural hearing loss (SNHL) often affects speech intelligibility, particularly in noisy environments or over telecommunication devices.
- Simulating telephone bandpass filtering (300-3000 Hz) is crucial for evaluating hearing aid and assistive listening device performance.
Purpose of the Study:
- To evaluate the effectiveness of digital signal processing (DSP) techniques in improving speech intelligibility for individuals with SNHL.
- To compare frequency domain and time domain processing methods for high-frequency hearing loss compensation.
- To assess user preference for different signal processing strategies in a simulated telephone listening condition.
Main Methods:
- 16 subjects with SNHL were tested using the California Consonant Test with digitized signals filtered to simulate telephone bandwidth.
- Signals were processed using frequency equalization and compression, as well as frequency domain and time domain DSP techniques.
- A second experiment involved 16 additional subjects comparing amplified signals with processed signals featuring emphasis, equalization, and loudness compression.
Main Results:
- Both frequency domain and time domain DSP techniques demonstrated significant improvements in speech intelligibility, ranging from 15% to 30%.
- In the second experiment, the majority of subjects with high-frequency hearing loss preferred the processed signal with 6 dB per octave emphasis over other strategies.
Conclusions:
- Digital signal processing offers a viable approach to enhance speech intelligibility for individuals with sensorineural hearing loss.
- Frequency equalization and compression, along with specific DSP algorithms, can effectively compensate for hearing-related deficits.
- Simple emphasis strategies may be preferred by users for telephone-based communication, highlighting the importance of user-centered design in hearing aid technology.