Thanks for the video. I have just slightly more understanding now. It seems the 5 channels are the available "instruments" so to speak of the NES. Am I correct that they play parallel to each other?
Unfortunately, the parameters such as pitch, vibrato, frequency, and width are still mysterious.
I think that these channel sounds are functions of pressure/time?
Probably the triangle channel is a /\-shaped function and the 0.5 pulse is a square. Music is always a mystery to me.