A voice limiter object restricts the number of MIDI notes (1 to 32) that can be held simultaneously.
It does this by note stealing—newly arriving notes cause (some of the) currently held notes to be turned off, once the voice limit is reached.
Choose New > Voice Limiter (or use the New Voice Limiter key command).
Normally, you assign a voice limiter to an arrange track, and cable its output to the instrument object that you want to voice limit. Alternately, you can cable it between the instrument object that you want to voice limit and an instrument object used to represent a MIDI Out port.