The development of a modified spectral ripple test

Abstract

Poor spectral resolution can be a limiting factor for hearing impaired listeners, particularly for complex listening tasks such as speech understanding in noise. Spectral ripple tests are commonly used to measure spectral resolution, but these tests contain a number of potential confounds that can make interpretation of the results difficult. To measure spectral resolution while avoiding those confounds, a modified spectral ripple test with dynamically changing ripples was created, referred to as the spectral-temporally modulated ripple test (SMRT). This paper describes the SMRT and provides evidence that it is sensitive to changes in spectral resolution.

Figure 1

(Color online) Comparison of the traditional ripple stimuli and the stimuli for the SMRT. Both the traditional and SMRT stimuli were generated using Eq. 1. (A) Spectrograms of reference and target stimuli for the traditional ripple task and the SMRT. (B) Spectrums of the high frequency edge, indicated by the dark rectangles next to the spectrograms in (A), for the two tasks. These spectrums indicate that, unlike with the traditional ripple task, there is no shift in the high frequency edge between the reference and target stimuli for the SMRT. (C) Spectrum of a portion of the frequency region, indicated by the light rectangles next to the spectrograms in (A). These spectrums indicate that local loudness cues are present in the traditional ripple task but absent in the SMRT. (D) Spectral centroid for the reference and target stimuli. These plots illustrate how the centroids for the target and masker differ in the traditional ripple task versus in the SMRT.

Figure 2

(Color online) Spectrograms of stimuli generated using Eq. 1 showing the orthogonal effects of manipulating the ripple repetition rate and the number of ripples per octave. The first column represents the ripple repetition rate used for the SMRT.

Figure 3

Results indicating that SMRT thresholds are sensitive to changes in spectral resolution. Circles and dashed lines indicate trimmed means. Error bars and gray areas indicate ±1 Winsorized standard error. Floor reflects performance with the wide 1 channel vocoder, at which point performance is based on temporal rather than spectral resolution. Unprocessed data indicates the ceiling for the vocoded version of the SMRT.