The time it takes for a note to fade out to silence, after the key has been released, is called the release time in synthesizers. Vintage B3 provides control of this parameter, known as sustain in organ terminology.
Upper Manual slider: Control the sustain (release) phase of the upper register.
Lower Manual slider: Control the sustain (release) phase of the lower register.
Pedals slider: Control the sustain (release) phase of the pedal register.
Mode buttons (Controls view only): Click to choose one of two sustain behaviors:
Smart: Cuts the sustain phase of released notes when you play new notes.
Normal: Allows polyphonic sustain phases. All released notes continue to sustain, even if new notes are played.
Note: Smart mode allows for long sustain times, even in the bass register, which would cause rumbling dissonances if you used normal mode.