0 to 100%
This parameter affects both reverberation and early reflections.
Diffusion determines the amount of sound reflections within the onset of a reverb and is most noticeable with more transient sounds.
A low to moderate setting yields a smoother initial reverb, with distinct reflections if Size (SIZ) is large (and therefore with lower density). This is preferable when you want clearer and more natural vocals, mixes, and piano music.
A higher setting gives a more distinct or grainy effect. This will enhance the sound of percussion or other sounds with sharp transients.