Music and Hearing Aids—An Introduction

Abstract

Modern digital hearing aids have provided improved fidelity over those of earlier decades for speech. The same however cannot be said for music. Most modern hearing aids have a limitation of their "front end," which comprises the analog-todigital (A/D) converter. For a number of reasons, the spectral nature of music as an input to a hearing aid is beyond the optimal operating conditions of the "front end" components. Amplified music tends to be of rather poor fidelity. Once the music signal is distorted, no amount of software manipulation that occurs later in the circuitry can improve things. The solution is not a software issue. Some characteristics of music that make it difficult to be transduced without significant distortion include an increased sound level relative to that of speech, and the crest factor-the difference in dB between the instantaneous peak of a signal and its RMS value. Clinical strategies and technical innovations have helped to improve the fidelity of amplified music and these include a reduction of the level of the input that is presented to the A/D converter.

The Effect of a High Upper Input Limiting Level on Word Recognition in Noise, Sound Quality Preferences, and Subjective Ratings of Real-World Performance

“…Most current 16-bit ADCs provide a 96-dB SPL input dynamic range (Chasin, 2006;Chasin, 2012;Hockley et al, 2012;Schmidt, 2012;Baekgaard, Knudsen, et al, 2013, Baekgaard, Rose, et al, 2013. The typical peak or upper input limiting level (UILL), which is the level at which the ADC peak clips and distorts the input signal, can range between 95 and 105 dB SPL (Kuk et al, 2014).…”

“…This suggests that if the input intensity of the signal is greater than the UILL, distortion will occur. If the original acoustic signal is not accurately represented after the ADC, the processed signal will remain distorted regardless of what manufacturer algorithm(s) is applied to the input signal (Chasin, 2006;Chasin, 2012;Baekgaard, Knudsen, et al, 2013, Baekgaard, Rose, et al, 2013. The typical UILL in most current hearing aids may be appropriate for soft (50 dB SPL) and average conversational speech (65 dB SPL) and perhaps even loud speech, which can reach a long-term root-mean-square (RMS) level of 80-90 dB SPL (Chasin, 2006;Hockley et al, 2012;Schmidt, 2012;Baekgaard, Knudsen, et al, 2013;Baekgaard, Rose, et al, 2013).…”

“…Of importance is the crest factor, which is the difference between the instantaneous peak input level and the RMS value of a signal. The crest factor of speech is 12 dB SPL, whereas, the crest factor for music ranges from 14 to 20 dB SPL (Chasin, 2012;Schmidt, 2012). Considering the typical RMS values for shouted speech (90 dB SPL) and music (105 dB SPL), the instantaneous peak levels for loud speech could be as high as 102 and 122 dB SPL for music.…”

Music and Hearing Aids

“…A special edition of Trends in Amplification ( Chasin & Hockley, 2012 ) was dedicated to the topic of music and hearing loss. Several of the articles were concerned with distortion caused by the high sound levels and crest factors that are typical of live music ( Chasin, 2012 ; Hockley, Bahlmann, & Fulton, 2012 ; Schmidt, 2012 ); the crest factor is the ratio of the peak value to the root mean square value. Chasin (2012) argued that distortion occurs because of the limited input dynamic range that can be handled by current analog-to-digital (A/D) converters.…”

Auditory perceptual efficacy of nonlinear frequency compression used in hearing aids: A review

“…The acoustics of speech and music bear enormous differences in aspects such as dynamic range, spectral nature, etc. ( Chasin and Russo, 2004 , Chasin, 2012 ). The input dynamic range for music is near 80 dB whereas that for speech is usually around 40 dB.…”