Here is a list of available effects in the HPD-20:
AMBIENCE
STEREO DELAY
SYNC DELAY
TAPE ECHO
CHORUS
SPACE-D
PHASER
STEP PHASER
FLANGER
STEP FLANGER
REVERB
LONG REVERB
EQUALIZER
COMP
SATURATOR
FILTER
FILTER + DRIVE
AUTO WAH
LO-FI COMP
OVERDRIVE
DISTORTION
BIT CRUSH
ISOLATOR
RINGMOD
PITCH SHIFT
AUTO PAN