Coherence measurements in hearing instruments, using different broad-band signals

Area of Science:

• Audiology
• Signal Processing
• Acoustics

Background:

• Non-linear distortion in hearing instruments can affect sound quality.
• Automatic signal processing (ASP) in hearing instruments aims to optimize audibility.
• Coherence measurements are a standard technique for assessing signal processing linearity.

Purpose of the Study:

• To investigate the impact of different broad-band test signals on non-linear distortion measurements in hearing instruments.
• To explore the interaction between test signals and automatic signal processing (ASP) in hearing instruments.
• To determine the validity of coherence measurements for quantifying non-linear distortion in hearing instruments with and without ASP.

Main Methods:

• Examined non-linear distortion in hearing instruments using coherence measurements.
• Utilized various broad-band test signals.
• Investigated the interplay between different test signals and ASP types.

Main Results:

• Coherence measurements are only valid for quantifying non-linear distortion in hearing instruments lacking automatic signal processing.
• The interaction between test signals and ASP introduces uncontrollable system time-variations.
• These time-variations significantly influence the measured coherence function, rendering it unreliable.

Conclusions:

• Coherence measurements are not a universally valid method for assessing non-linear distortion in modern hearing instruments with ASP.
• The presence of ASP fundamentally alters the system's behavior in response to different test signals.
• Future research should consider alternative or modified measurement techniques for hearing instruments with complex signal processing.