Yamaha VL-1 Feature Reference page 56

Output Level
Distortion
Sets the output level of the distortion sound. Higher values produce higher level.
Speaker
Simulates a variety of speaker types and configurations via which the distortion
sound might be reproduced.
Flat
Stack
Combo
Twin
Radio
Megaphone
Presence
Varies the "presence" or "brilliance" of the sound. Higher values produce more
presence and "punch".
Feature Reference Edit Mode
No speaker — the sound of a "direct feed" to a recording or sound
reinforcement console.
The powerful, expansive sound of stacked speaker cabinets.
A single 12" speaker unit in an open-backed enclosure.
Two 12" speaker units in a relatively small open-backed enclosure.
The small, compressed, but pleasant tone of a radio receiver.
Constricted tone with emphasis on the middle frequencies.
Distortion Effect Block Diagram
L In
Distortion
R In
L Out
R Out