The triangle channel produces a smooth, sub-bass waveform. Because the NES hardware lacked volume control for this channel, it is either completely on or completely off.
If you are still using version 1.0 or an older clone, here is why you need to upgrade immediately.
This section is perfect for creating classic blistering chiptune leads or rapid-fire arpeggios that mimic chords. 2. Triangle Wave Generator
NES VST 1.1: The Ultimate Guide to Authentic 8-Bit Nintendo Sounds