Analog-to-Digital Conversion to Accommodate the Dynamics of Live Music in Hearing Instruments

Abstract

Hearing instrument design focuses on the amplification of speech to reduce the negative effects of hearing loss. Many amateur and professional musicians, along with music enthusiasts, also require their hearing instruments to perform well when listening to the frequent, high amplitude peaks of live music. One limitation, in most current digital hearing instruments with 16-bit analog-to-digital (A/D) converters, is that the compressor before the A/D conversion is limited to 95 dB (SPL) or less at the input. This is more than adequate for the dynamic range of speech; however, this does not accommodate the amplitude peaks present in live music. The hearing instrument input compression system can be adjusted to accommodate for the amplitudes present in music that would otherwise be compressed before the A/D converter in the hearing instrument. The methodology behind this technological approach will be presented along with measurements to demonstrate its effectiveness.Keywords hearing aids, hearing instruments, live music, musicians and hearing loss A/D conversion peak sound pressure level of music

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).…”

“…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). The typical UILL, however, may be limiting for high input signals, such as loud speech as a result of the Lombard Effect (Lombard, 1911), which is an increase in vocal effort to improve speech recognition in background noise, or when speech is amplified through a loudspeaker system.…”

“…While hearing aids may have been optimized for speech, patients are in dynamic environments and require hearing aids that can provide benefit for sounds other than speech, such as listening to music. Music in particular can reach very high intensity levels with RMS of 100-105 dB SPL (Chasin, 2006;Hockley et al, 2012;Schmidt, 2012;Baekgaard, Knudsen, et al, 2013;Baekgaard, Rose, et al, 2013).…”

The Effects of Extended Input Dynamic Range on Laboratory and Field-Trial Evaluations in Adult Hearing Aid Users

“…Digital hearing aids using a 16-bit ADC provide a 96-dB input dynamic range (Chasin, 2006;Hockley et al, 2012;Schmidt, 2012;Baekgaard, Knudsen, et al, 2013;Baekgaard, Rose, et al, 2013). In current digital hearing aids, the input level at which the ADC peak clips and distorts input signals ranges between 95 and 105 dB SPL (Kuk et al, 2014).…”

“…This suggests that many input signals commonly encountered by hearing aid users should be accurately reflected by the ADC in digital format to the DSP. As a result, hearing aid users exposed to conversational speech ranging in level from 50 dB SPL (soft) to 80 dB SPL (loud) are unlikely to perceive any distortion due to ADC peak clipping (Chasin, 2006;Hockley et al, 2012;Schmidt, 2012;Baekgaard, Knudsen, et al, 2013;Baekgaard, Rose, et al, 2013).…”