Accordingly, if the materials present preferentially absorb high-frequency energy, then energy at high frequencies is expected to decay quicker than at low frequencies. It turns out that air absorbs acoustic energy, reducing high frequencies much quicker than low frequencies. There are a relatively small number of psychoacoustic parameters which are needed to describe the source and environment. Direction and distance describe the source position, and are related to the direct path direction and the relative direct path, early reflection, and late-field levels. Source brilliance and warmth are determined by the early energy equalization.
Intimacy describes the remoteness or intimacy of the space.
Reverberance has two aspects. Running reverberance is heard during continuous sounds, whereas late reverberance is heard during breaks in the source signal. Room heaviness and liveliness are specified by the variation in T60 as a function of frequency. Spaciousness and envelopment depend on the percentage of early energy arriving laterally and the crosscorrelation of late-field energy heard at the left and right ears of a listener. Large lateral energy portions and small crosscorrelations correspond to spacious, enveloping environments.