Hey Jesse!

I believe the C64-like sound you’re referring to is the arpeggio effect, although there are a couple things about the MC Kids music that are reminiscent of the C64. I like to call this kind of NES music “Euro Style”, because of the direct impact the C64 had on Western composers’ sound design.

The arpeggio effect is chipmusic’s solution for simulating a chord in a single channel. It is very prohibitive to arrange “true” chords for the NES, because generally speaking you can only play 3 notes at a time. And you’d probably want the different channels doing something more interesting than working together to combine one simultaneous chord.

Since that rules out a practical use for conventional chords, the arpeggio effect works by using fast, broken chords. Instead of playing the notes “D F A” at the same time, you can have one channel alternate rapidly between those notes, kind of like how a classic telephone ring sounds. 

This was particularly present in C64 music, because it only had three channels (versus the NES’ 5, although it was much more versatile in other ways…). Cramming as much as you could into one channel was important on the C64, and that helped give birth to a style of vgm that drips with arps. [Example - Myth C64, by Jeroen Tel]

Anyways, I opened up the M.C. Kids Level 4 track and examined the first arpeggio:

^This is the volume envelope. There’s nothing particularly special or C64-like about it. It has a little volume bump instead of having an uninterrupted fade, which adds some detail to the sound.

^This is the arpeggio table/envelope, responsible for bringing the C64-ness.

The frame rate of the NTSC NES/Famicom is 60fps, which is the standard resolution at which you can manipulate sounds. Anything can change that fast on the NES, including pitch, which is what allows these fast arpeggios. On the bar graph above, every bar lasts 1/60th of a second (revealing that each note lasts 2/60ths). The first two bars are the root note of the chord, then each available space represents the nearest half-step on a keyboard. So it jumps up 4 half steps, then 3 more (7 from the original note). If you’re musically inclined, this particular arpeggio effect is creating a major triad.

^And lastly, there is a looped modulating set of duty cycles, which contributes to the voice sounding Western (it’s not uncommon for Japanese soundtracks to use changing duty cycles, but they usually don’t loop constantly).

If you’ve watched the introduction to the NES sound channels video below, you saw a quick explanation of the different “instruments” that the pulse wave channels can be. There’s 12.5%, 25%, 50%, and 75%. The graph doesn’t make it clear, but that’s the Y-axis here. 0 = you’re using the 12.5% voice, 1 = 25%, etc.

Another way to think of it- as the note sustains, it is “changing instruments” repeatedly.

For the famitracker/ MML-using readers, here’s the instrument data:

• Volume: 0 8 6 6 5 4 4 4 4 4 4 4 4 4 3 2 3 4 4 4 4 4 3 3 3 3 3 2 2 2 2 2 0 
• Arpeggio: | 0 0 4 4 7 7 
• Duty Cycle: 2 2 2 2 2 2 2 | 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 2 2 2 2 2 2

I hope that wasn’t a needlessly long response, but this was the perfect opportunity to elaborate on a couple concepts. MC Kids also does neat stuff like triangle channel kick drums, but that’s a topic for a future post.

I’ll close with my favorite track from MC Kids. :)