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Abstract
This study examined the effect that signal processing strategies used in modern hearing aids, such as multi-channel WDRC, noise reduction, and directional microphones have on interaural difference cues and horizontal localization performance relative to linear, time-invariant amplification. Twelve participants were bilaterally fitted with BTE devices. Horizontal localization testing using a 360° loudspeaker array and broadband pulsed pink noise was performed two weeks, and two months, post-fitting. The effect of noise reduction was measured with a constant noise present at 80° azimuth. Data were analysed independently in the left/right and front/back dimension and showed that of the three signal processing strategies, directional microphones had the most significant effect on horizontal localization performance and over time. Specifically, a cardioid microphone could decrease front/back errors over time, whereas left/right errors increased when different microphones were fitted to left and right ears. Front/back confusions were generally prominent. Objective measurements of interaural differences on KEMAR explained significant shifts in left/right errors. In conclusion, there is scope for improving the sense of localization in hearing aid users.
| Acronyms | ||
| A/D | = | Analogue to digital |
| ANOVA | = | Analysis of variance |
| B&K | = | Brüel and Kjær |
| BTE | = | Behind-the-ear |
| D/A | = | Digital to analogue |
| F/B | = | Front/back |
| FF | = | Free field |
| FFT | = | Fast Fourier transform |
| HL | = | Hearing level |
| ILD | = | Interaural level difference |
| ILTASS | = | International long-term average speech spectrum |
| ITD | = | Interaural time difference |
| ITE | = | In-the-ear |
| ITC | = | In-the-canal |
| KEMAR | = | Knowles Electronics Manikin for Acoustic Research |
| Leq | = | Long-term root-mean-square level |
| L/R | = | Left/right |
| NAL-NL1 | = | National Acoustic Laboratories non-linear version 1 |
| P | = | Decomposed presentation azimuth in the 360° horizontal plane |
| R | = | Decomposed response azimuth in the 360° horizontal plane |
| REIG | = | Real-ear insertion gain |
| REUR | = | Real-ear unaided response |
| RMS | = | Root-mean-square |
| SNR | = | Signal-to-noise ratio |
| SPL | = | Sound pressure level |
| SQRT | = | Square root |
| WDRC | = | Wide dynamic range compression |
| 3FA | = | Three-frequency average hearing threshold level measured across 500, 1000, and 2000 Hz |
| Acronyms | ||
| A/D | = | Analogue to digital |
| ANOVA | = | Analysis of variance |
| B&K | = | Brüel and Kjær |
| BTE | = | Behind-the-ear |
| D/A | = | Digital to analogue |
| F/B | = | Front/back |
| FF | = | Free field |
| FFT | = | Fast Fourier transform |
| HL | = | Hearing level |
| ILD | = | Interaural level difference |
| ILTASS | = | International long-term average speech spectrum |
| ITD | = | Interaural time difference |
| ITE | = | In-the-ear |
| ITC | = | In-the-canal |
| KEMAR | = | Knowles Electronics Manikin for Acoustic Research |
| Leq | = | Long-term root-mean-square level |
| L/R | = | Left/right |
| NAL-NL1 | = | National Acoustic Laboratories non-linear version 1 |
| P | = | Decomposed presentation azimuth in the 360° horizontal plane |
| R | = | Decomposed response azimuth in the 360° horizontal plane |
| REIG | = | Real-ear insertion gain |
| REUR | = | Real-ear unaided response |
| RMS | = | Root-mean-square |
| SNR | = | Signal-to-noise ratio |
| SPL | = | Sound pressure level |
| SQRT | = | Square root |
| WDRC | = | Wide dynamic range compression |
| 3FA | = | Three-frequency average hearing threshold level measured across 500, 1000, and 2000 Hz |
Sumario
Este estudio examinó el efecto que las estrategias de procesamiento de señales usadas en los auxiliares auditivos modernos, como el WDRC multicanal, la reducción de ruido y los micrófonos direccionales, tienen sobre las pautas de diferencias interaurales y sobre el rendimiento para la localización, en relación con la amplificación linear o invariante en el tiempo. Doce participantes fueron adaptados bilateralmente con instrumentos BTE. Se efectuó una prueba de localización horizontal usando un sistema de altoparlantes de 360° y un ruido rosa pulsado de banda ancha, a las dos semanas y a los dos meses de la adaptación. El efecto de reducción de ruido se midió con la presentación de un ruido constante en azimut de 80°. Los datos se analizaron de manera independiente en las dimensiones izquierda/derecha y adelante/atrás y mostraron que de las tres estrategias de procesamiento de señales, los micrófonos direccionales tienen el efecto mas significativo en el rendimiento para la localización horizontal y en el tiempo. Específicamente, un micrófono cardioide puede disminuir los errores adelante/atrás en el tiempo, mientras que los errores izquierda/derecha aumentan cuando se pusieron micrófonos diferentes en los oídos derecho e izquierdo. Las confusiones adelante/atrás fueron generalmente prominentes. Las mediciones objetivas de las diferencias interaurales en KEMAR explicaron las variaciones significativas en los errores izquierda/derecha. En conclusión, existen posibilidades de mejorar las habilidades de localización en usuarios de auxiliares auditivos.
