Role of Reverberation in Distance Perception

In visual perception, if one sees a larger object far and a smaller object near, their relation can be recognized from context. Aural perception includes analogous effects. The magnitude of a sound is source intensity, having a physical, objective value. But the perceived source level is loudness, a mental perception. If small source intensity is close to a listener, it is recognized as such through reverberation, which serves as the context as in visual perception. Since reverberation is the environmental context, it must be constant across distance, as suggested by Figure 3 depending only on source intensity [KMW90].

  

Figure 3: Constant Reverberation

The following are equations for source and reverberation as a function of distance and loudness in the PSFC, using loudness and distance look-up tables, created through psychoacoustic calibrations:

$$\begin{eqnarray*}Src_{\mbox{gain}} &=& Src_{\mbox{level}} + L(loudness) + \,D(distance) \\ Rev_{\mbox{gain}} &=& Rev_{\mbox{level}} + L(loudness) \end{eqnarray*}$$

The $Src_{\mbox{gain}}$ is input to the PSFC to control final source level, VOLUME. $Rev_{\mbox{gain}}$ is the input to PSFC to control the final reverb level, LIVENESS. (Both $Src_{\mbox{level}}$ and $Rev_{\mbox{level}}$ are maxima in dB.) The $D\,(distance)$ and $L\,(loudness)$ are look-up tables, shown in Figure 4. The $Src_{\mbox{gain}}$ depends on the distance, so the adjustment must include both distance and loudness. Note that $Rev_{\mbox{gain}}$ does not depend on the distance.

  

Figure 4: left) distance look-up table, right) loudness look-up table