AHDSFR is an abbreviation for Attack, Hold, Decay, Sustain, Fade, and Release. These are six parameters found on some advanced synthesizer envelope generators. An envelope generator is used to control sound parameters over time, usually the manner in which a sound starts, continues and disappears. The Attack, Hold, Decay, and Release parameters are rate or time controls. Attack is the beginning of the sound. Hold is the amount of time the Attack value is maintained before going to the decay state. Decay is the manner in which sound ceases. Sustain is a level control. On a synthesizer, when a key is pressed, the envelope generator will begin to rise to its full level at the rate set by the attack parameter, upon reaching peak level it will begin to fall at the rate set by the decay parameter to the level set by the sustain control. The envelope will remain at the sustain level as long as the key is held down. Fade, is a parameter that gives you the option to fade the sustain portion of the signal to maximum or minimum level. The final portion of the envelope is release, which is the rate at which the signal returns to zero after a key is released.