The Influence of the Stimulus Level Used to Prescribe Nonlinear Frequency Compression on Speech Perception

Area of Science:

• Audiology
• Signal Processing
• Hearing Aid Technology

Background:

• Nonlinear frequency compression (NFC) is a signal processing technique that shifts inaudible high-frequency sounds to audible lower frequencies.
• The optimal input level for setting NFC is critical, as individual hearing loss affects the audible frequency range.
• Varying input levels for NFC calibration can impact speech recognition performance in hearing-impaired listeners.

Purpose of the Study:

• To investigate the impact of different input speech levels used for setting NFC on nonsense syllable recognition.
• To determine the optimal input level for calibrating NFC to maximize speech intelligibility.

Main Methods:

• Nonsense syllable recognition was assessed in 23 adults with hearing loss using a hearing aid simulator.
• NFC was set at three input levels: 50, 60, and 70 dB SPL, with a restricted bandwidth condition as a control.
• Speech stimuli (consonant-vowel-consonant nonwords) were presented in noise, and recognition was scored across different speech components.

Main Results:

• Nonsense syllable recognition improved with increasing presentation levels.
• The highest recognition scores were achieved when NFC was set using a 70 dB SPL input level.
• Recognition decreased significantly when NFC was set at 50 or 60 dB SPL, with vowels being more affected than consonants.

Conclusions:

• Setting NFC based on a higher input level (70 dB SPL) yields superior nonsense syllable recognition.
• A high presentation level is recommended for determining NFC parameters to optimize speech recognition for hearing-impaired individuals.
• The findings suggest that input level selection is a crucial factor in NFC fitting for effective hearing aid use.