Alesis S4 Plus Reference Manual page 101

Chapter 7: Editing Effects
Reverb (Page 4)
Density
Density controls how the first reflection of the reverb effect will appear. When set to 0,
the first reflection is heard alone without any other reflections. When set to 99, the
first reflection appears to "fade-in" and then "fade-out". This is because a number of
reflections will occur just before and just after the first reflection, in addition to the
remaining reflections heard after the first reflection. Thus, the reverb sounds more
"dense".
If the select Reverb type is Large, the Density parameter is unavailable.
Diffusion
Diffusion determines the "thickness" of the reverb sound by adding more reflections
to the reverb's decay. With lower diffusion settings, you may be able to actually hear
the individual echoes that make up the overall reverb sound. With higher diffusion
settings, the echoes increase in number and blend together, washing out the reverb's
decay. Greater diffusion works better with percussive sounds, whereas less amounts
of diffusion work well with vocals and other sustained sounds.
L
E
V
E
L
Note: The illustration above reflects a Density setting of 0.
100
DIFFUSION OF 0
TIME
Fewer reflections
DIFFUSION OF 99
L
E
V
E
L
TIME
More reflections
S4 Plus Reference Manual