triggers the envelope and holds it open while greater
                        than zero. A value of less than zero enforces a release
                        with duration -1.0 - gate .
duration (seconds) of the attack segment
level of the sustain segment
duration (seconds) of the release segment
action to be performed when the envelope reaches its end point.
      
    
      
    
      
    
      
      
    
      
      
    
      
      
    
      
      
    
      
      
    
      
      
    
      
      
    
      
A linear ASR-type envelope generator UGen.
Examples
EnvGen