Loudness perception sums auditory bands and signals distance by comparison

Evidence

A broadband sound is perceived to be louder than sound with a narrower band of equal sound pressure level, as shown by both the phenomenon used to define Bark bands in Section 9.4.1 and the higher loudness generated by white noise than a sinusoid shown in Figure 10.8. Our hearing thus analyses the loudness of different auditory bands separately and adds the obtained results to form a total loudness for the system, which turns out to be higher than it should be in principle. This implies that the mechanism detecting loudness accounts for the effect of the inherent broadening of the excitation of narrowband signals in the basilar membrane. It can be assumed that the mechanism uses the broadening as a loudness cue, and higher loudness is analysed with broader frequency content. This makes the system measuring the loudness dependent on the signal bandwidth itself, which could be thought to be an issue. However, very possibly this does not cause any deficiencies in the perception of the surrounding world, since no large evolutionary advantage can be seen to occur if the loudness of sound was not dependent on the spectral content of sound. On the other hand, an important task of hearing is to estimate if a sound source is approaching or if its distance is changing in general. In such cases, the loudness of the auditory event is compared to earlier similar events, and the relative loudness gives the cue of distance. Such a comparison does not require an accurate estimate of the sound pressure level, and thus a relative difference is already very usable. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1142

Categorization

• XREF: Connects to earlier chapters on loudness models (ch 10 loudness formulas) and to the distance-estimation function of hearing mentioned in other psychoacoustics sources.
• QUESTION: The claim that loudness dependence on bandwidth carries no evolutionary deficiency — worth interrogating whether broadband-specific loudness could aid predator/prey distance assessment in ways not explored here.