Based on perceptual limits, the impulse response of a reverberant space can be divided into two segments:
The beginning of the impulse response consists of distinct, relatively sparse, early reflections.
The remainder of the impulse response, called the late reverberation, consists of densely-packed echoes which become impossible to distinguish in time.
The frequency response of a reverberant space can likewise be divided into two segments:
The low-frequency region consists of a relatively sparse distribution of resonant modes.
Higher-frequency modes are packed so densely that they are best characterized by a random frequency distribution with certain statistical properties.
Parametric controls for an artificial reverberator should include:
in at least three frequency bands
“clarity” (ratio of impulse response energy in early reflections to that in the late reverb section)
inter-aural correlation coefficient at the left and right ears