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Original Article

SII and fit-to-target analysis of compression system performance as a function of number of compression channels

SII y análisis de adaptación a meta del desempeño de un sistema de compresión como función del numero de canales de compresión.

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Pages 630-644 | Published online: 07 Jul 2009
 

Abstract

This work was undertaken to answer the question, ‘How does the speech audibility/fit-to-gain-target provided by compression change with number of channels?’ For each of 957 audiograms and a given number of compression channels, the channel crossover frequencies were set either to maximize the SII (speech intelligibility index) for low- and high-level speech spectra, or to optimize the fit-to-gain targets from the Cambridge method for loudness equalization (CAMEQ). The audiograms comprised all common configurations, and losses ranged from mild to severe. Use of these computational procedures allowed the predicted, channel-number-based performance to be determined separately from the effects of other compression parameters. From one to five channels were sufficient to yield predicted speech recognition performance within 5% of maximum for 90% of the ‘mild’ and ‘moderate’ audiograms. Three to nine channels were necessary for the same level of predicted performance for 90% of the ‘severe’ audiograms. Four channels or fewer were sufficient to produce less than 5 dB rms error in fit to CAMEQ targets for 90% of all audiograms.

Sumario

Este trabajo se llevó a cabo para responder a la pregunta “¿Como cambia con el numero de canales la audibilidad/ganancia meta de acuerdo a la compresión? Para cada uno de los 957 audiogramas y un número dado de canales de compresión, se fijaron las frecuencias de intersección para maximizar el índice de inteligibilidad del lenguaje para espectros de habla de alta y baja intensidad o para optimizar el blanco justo a la ganancia a partir del método Cambridge para ecualización de sensación subjetiva de intensidad (CAMEQ). Los audiogramas presentaban todas las configuraciones y las pérdidas variaban de leve a severas. El uso de procedimientos computacionales nos permitió predecir en forma separada el desempeño por número de canales del efecto de otros parámetros de compresión. De uno a cinco canales fue posible predecir el desempeño alrededor del 5% con un reconocimiento máximo de 90% para los audiogramas con pérdida leve a moderada. Fueron necesarios de tres a nueve canales para obtener el mismo nivel de desempeño en la predicción de. 90% de las pérdidas severas. Fue suficiente con cuatro canales o menos para producir errores de menos de 5dB rms en la adaptación de metas CAMEQ del 90% de todos los audiogramas.

Acronyms
ANSI=

American National Standards Institute

CR=

Compression ratio

PB=

Phonetically balanced

PTA=

Pure-tone average

RAA=

Residual auditory area

REAG=

Real ear aided gain

RMS=

Root-mean square

SII=

Speech intelligibility index

ULCL=

Upper limit of comfortable loudness

WDRC=

Wide dynamic range compression

%C=

Percent correct

Acronyms
ANSI=

American National Standards Institute

CR=

Compression ratio

PB=

Phonetically balanced

PTA=

Pure-tone average

RAA=

Residual auditory area

REAG=

Real ear aided gain

RMS=

Root-mean square

SII=

Speech intelligibility index

ULCL=

Upper limit of comfortable loudness

WDRC=

Wide dynamic range compression

%C=

Percent correct

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