For those who want to try it out, you can also access these sounds in a somewhat easier way by using an NES audio emulator in your favorite DAW, or by using one of the various tracker programs:

https://www.mattmontag.com/projects-page/nintendo-vst

http://famitracker.com

This one lets you play the bass on the left hand of a keyboard and the square waves (should really be PWM) on the right hand:

https://aframe.itch.io/famikondo

Further, FYI: famitracker has a few different variants, with DN–famitracker being the fork, currently closest to accurately reproducing, the NES and the most common extant sound expansion chips: https://github.com/Dn-Programming-Core-Management/Dn-FamiTra...

And Famistudio is an excellent alternative if you prefer composing on a piano roll: https://famistudio.org