Rippled-spectrum resolution dependence on frequency: Estimates obtained by discrimination from rippled and nonrippled reference signals

Ripple density resolution dependence on ripple width

The goal of the study was to investigate how variations in ripple width influence the ripple density resolution. The influence of the ripple width was investigated with two experimental paradigms: (i) discrimination between a rippled test signal and a rippled reference signal with opposite ripple phases and (ii) discrimination between a rippled test signal and a flat reference signal. The ripple density resolution depended on the ripple width: the narrower the width, the higher the resolution. For distinguishing between two rippled signals, the resolution varied from 15.1 ripples/oct at a ripple width of 9% of the ripple frequency spacing to 8.1 ripples/oct at 64%. For distinguishing between a rippled test signal and a non-rippled reference signal, the resolution varied from 85 ripples/oct at a ripple width of 9% to 9.3 ripples/oct at a ripple width of 64%. For distinguishing between two rippled signals, the result can be explained by the increased ripple depth in the excitation pattern due to the widening of the inter-ripple gaps. For distinguishing between a rippled test signal and a non-rippled reference signal, the result can be explained by the increased ratio between the autocorrelated and uncorrelated components of the input signal.

High Ripple-Density Resolution for Discriminating Between Rippled and Nonrippled Signals: Effect of Temporal Processing or Combination Products?

The goal of the study was to investigate the role of combination products in the higher ripple-density resolution estimates obtained by discrimination between a spectrally rippled and a nonrippled noise signal than that obtained by discrimination between two rippled signals. To attain this goal, a noise band was used to mask the frequency band of expected low-frequency combination products. A three-alternative forced-choice procedure with adaptive ripple-density variation was used. The mean background (unmasked) ripple-density resolution was 9.8 ripples/oct for rippled reference signals and 21.8 ripples/oct for nonrippled reference signals. Low-frequency maskers reduced the ripple-density resolution. For masker levels from -10 to 10 dB re. signal, the ripple-density resolution for nonrippled reference signals was approximately twice as high as that for rippled reference signals. At a masker level as high as 20 dB re. signal, the ripple-density resolution decreased in both discrimination tasks. This result leads to the conclusion that low-frequency combination products are not responsible for the task-dependent difference in ripple-density resolution estimates.

Effect of level on spectral-ripple detection threshold for listeners with normal hearing and hearing loss

This study investigated the effect of presentation level on spectral-ripple detection for listeners with and without sensorineural hearing loss (SNHL). Participants were 25 listeners with normal hearing and 25 listeners with SNHL. Spectral-ripple detection thresholds (SRDTs) were estimated at three spectral densities (0.5, 2, and 4 ripples per octave, RPO) and three to four sensation levels (SLs) (10, 20, 40, and, when possible, 60 dB SL). Each participant was also tested at 90 dB sound pressure level (SPL). Results indicate that level affected SRDTs. However, the effect of level depended on ripple density and hearing status. For all listeners and all RPO conditions, SRDTs improved from 10 to 40 dB SL. In the 2- and 4-RPO conditions, SRDTs became poorer from the 40 dB SL to the 90 dB SPL condition. The results suggest that audibility likely controls spectral-ripple detection at low SLs for all ripple densities, whereas spectral resolution likely controls spectral-ripple detection at high SLs and ripple densities. For optimal ripple detection across all listeners, clinicians and researchers should use a SL of 40 dB SL. To avoid absolute-level confounds, a presentation level of 80 dB SPL can also be used.