I just implemented vibrato in the music engine and it sounds amazing! If things keep going like this, there really won't be any game, just a kickass NES audio emulator.
Here is a demo I just made of what will be the intro music: https://functional.cafe/@BTowersCoding/111293828453032032
The funny part of the experience was how naively I went into it. This is a running theme with me... there's usually a "right" way, which is way beyond my grasp, and then there's what the South Park creators used to call "dummy mode".
I knew that the idea was to use a sine wave to adjust the frequency of the note. But I didn't have any idea how much to adjust it, so when I played the first attempt, it sounded like... FM distortion. Surely I wasn't even on the right track.
Out of curiosity, I started changing the values. It sounded even weirder! Almost like the "Blaster Beam" used in the Star Trek movie for the Klingon/V'ger theme. Totally sick, but unfortunately not what I was intending at all. I was going for a beautiful flute-like sound like in the Legend of Zelda title theme.
Then I entered in a completely different value (for the same parameter), and... WHAT?!? It sounded sort of like vibrato! Could it be I was just off by a factor of 1000?
You be the judge (whoever you are...), listen to the demo above and tell me if I succeeded.