Spectro-Temporal Weighting of Loudness

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.

Preparation of stimuli for timbre perception studies

“…These calculate the contribution of individual harmonics using the critical band rate scale, so that lower harmonics fall in different critical bands, but higher harmonics may fall into the same critical band. This means that higher frequency components in the spectrum contribute less to loudness, as is also seen in the data of Oberfeld et al (2012). So, as the spectral centroid shifts toward higher frequencies, there will be a point at which the slope of loudness increase will flatten, as observed in the present data.…”

Perceptual weights for loudness judgments of six-tone complexes

“…The increased weight assigned to low frequencies might then be attributed to the presence of steeper loudness functions at low frequencies. Oberfeld et al (2012) considered this explanation for the low-frequency effect observed in their data and found that the predicted effect on perceptual weights was smaller than the observed effect. For the present conditions, any effect of steeper loudness functions at low frequencies should have been observed in the predictions generated by the model because it assumes steeper loudness functions at low frequencies, although the difference at 250 Hz is small.…”

“…Most of the previous uses of sample discrimination have given listeners correct-answer feedback (e.g., Doherty and Lutfi, 1996;Lutfi and Jesteadt, 2006;Oberfeld et al, 2012), and all but Oberfeld et al described it to listeners as an intensity resolution task rather than one involving judgments of overall loudness. Results reported here may have been different if the listeners had been given a more complete description of the properties of the stimuli and feedback regarding their answers, but the intent was to make the loudness and sample-discrimination tasks comparable, not to emphasize potential differences.…”

“…Together these results suggest that differences in level rather than degree of hearing loss may have accounted for the differences in perceptual weight obtained by Doherty and Lutfi (1996) at higher frequencies. Oberfeld et al (2012) obtained perceptual weights for both time and frequency using stimuli made up of three noise bands divided into ten temporal segments. Their listeners were tested in a single-interval sample discrimination task in which they indicated their confidence that a loud or soft sound had been presented.…”

Temporal loudness weights for sounds with increasing and decreasing intensity profiles

“…So far, temporal weights of loudness have been assessed mainly for sounds with flat intensity profiles (e.g., Pedersen and Ellermeier, 2008;Oberfeld and Plank, 2011;Oberfeld et al, 2012). Using experimental designs based on molecular a) Author to whom correspondence should be addressed.…”