Spectro-temporal weighting of loudness.

Daniel Oberfeld,Jesko Verhey,Jan Rennies,Wiebke Heeren,Joel Snyder

doi:10.1371/journal.pone.0050184

Abstract

Real-world sounds like speech or traffic noise typically exhibit spectro-temporal variability because the energy in different spectral regions evolves differently as a sound unfolds in time. However, it is currently not well understood how the energy in different spectral and temporal portions contributes to loudness. This study investigated how listeners weight different temporal and spectral components of a sound when judging its overall loudness. Spectral weights were measured for the combination of three loudness-matched narrowband noises with different center frequencies. To measure temporal weights, 1,020-ms stimuli were presented, which randomly changed in level every 100 ms. Temporal weights were measured for each narrowband noise separately, and for a broadband noise containing the combination of the three noise bands. Finally, spectro-temporal weights were measured with stimuli where the level of the three narrowband noises randomly and independently changed every 100 ms. The data consistently showed that (i) the first 300 ms of the sounds had a greater influence on overall loudness perception than later temporal portions (primacy effect), and (ii) the lowest noise band contributed significantly more to overall loudness than the higher bands. The temporal weights did not differ between the three frequency bands. Notably, the spectral weights and temporal weights estimated from the conditions with only spectral or only temporal variability were very similar to the corresponding weights estimated in the spectro-temporal condition. The results indicate that the temporal and the spectral weighting of the loudness of a time-varying sound are independent processes. The spectral weights remain constant across time, and the temporal weights do not change across frequency. The results are discussed in the context of current loudness models.

Highlights

Loudness is the sensation which is most closely related to the intensity of a sound
area under the receiver operating characteristic (ROC) curve (AUC) and its variance were computed from the maximumlikelihood (ML) estimates of slope and intercept of the ROC curve, using the delta method [72]
Summary and Conclusions A limitation of previous studies concerned with the decision weights listeners apply when judging the loudness of complex sounds is that they either considered the temporal weighting of loudness but did not look at spectral weights, or measured spectral weights but did not consider temporal aspects of loudness

Summary

Introduction

Loudness is the sensation which is most closely related to the intensity of a sound. loudness depends on other characteristics of the sound such as its duration or its spectral content. Several studies demonstrated that at equal sound pressure level a broadband signal is usually louder than a narrow-band signal (e.g., [1,2,3,4,5,6,7,8,9]) This effect is commonly referred to as spectral loudness summation. Apart from the integration across frequency, the auditory system seems to integrate over time: The level of a short signal is usually higher than the level of an loud long signal with the same spectrum [13,14,15,16,17] This temporal integration is usually accounted for by assuming a leaky integrator as a temporal integration stage and a decision device that uses the maximum or a percentile of the output of this stage. Current elaborate loudness models include both a spectral and a temporal stage of the kind described above to account for loudness of time-varying sounds like speech or the noise of a vehicle passing by (e.g., [18,19])

Results

Discussion

Conclusion