The just-noticeable difference in speech-to-noise ratio

Area of Science:

• Auditory perception
• Speech processing
• Hearing science

Background:

• Just-noticeable differences (JNDs) are established for many sound features, but not for speech-to-noise ratio (SNR).
• SNR is critical for speech intelligibility, especially for hearing-impaired individuals, impacting satisfaction with hearing devices.
• Current hearing-assistance device improvements lack a benchmark for noticeable SNR benefit.

Purpose of the Study:

• To establish a benchmark for the just-noticeable difference (JND) in speech-to-noise ratio (SNR).
• To determine the minimum SNR improvement required for a perceptible benefit in speech clarity.
• To compare SNR JNDs between normal-hearing and hearing-impaired listeners.

Main Methods:

• Measured SNR JNDs in 69 participants with varying hearing abilities using adaptive and fixed-level procedures.
• Participants judged sentence clarity in speech-spectrum noise presented over headphones.
• Headphone presentation levels were roved to minimize reliance on absolute level cues.

Main Results:

• The average SNR JND was 3 dB, consistent across participants regardless of hearing ability.
• Both adaptive and fixed-level procedures yielded similar 3 dB JND results.
• Further experiments indicated that level roving can influence thresholds.

Conclusions:

• A 3 dB improvement in SNR is the minimum threshold for a noticeable difference in speech clarity.
• Noise reduction schemes in hearing devices should aim for benefits exceeding 3 dB for reliable discrimination.
• The findings provide a crucial benchmark for evaluating the efficacy of hearing assistance technologies.