RE: C64 vs Famicom music:
I think there are two issues that intertwine - less channels, and more flexibility, which led to poorly chosen ways of working around there being less channels.
There’s two types of warble. One is the oscillating between two notes, the other is the note bending all off the place in various types of vibrato. The first sounds outright bad IMO, the second is just used badly a lot but can be good. The reason C64 coders used the oscillating warble a lot (and yes they did use it when they made NES games too, maybe out of habit/Stockholm syndrome or maybe their tools were set up for C64 and they just used the same ones) was the C64 only had three channels as the warble between two notes acted as proxy chord when you had no spare musical space free.
C64 music cut out for sound effects more often for the same reason (or skimped on sound effects), only three channels. So while a track may sound okay, it’s not usable in gameplay unless you have no sound effects. This is an issue Mark III FM games have too, as FM only has three channels, but they’re really nice instruments in that case vs standard Mark III/MS audio which is pretty scabby so it’s still an improvement there.
Essentially the Famicom has four channels (or two more available by expansion as the cart slot had a direct audio connection, which hundreds of Fami games used but the NES lost), but those channels were specifically chosen to be nice instruments for music and sound effects. Only two are really flexible, so yes a lot of the music on the system sounds similar. Two are basically only usable as drums and bass (or crunchy or bassy sound effects), so most Fami games get a drums and bass by default, which may be rigid but is a solid bedrock.
C64 has three flexible channels, but a) the flexibility allows for too much freedom by people with poor taste and b) three is just not enough for a game, as you can only really use two for music.
Every time I have this discussion I look up ‘best of C64 music’ and find a bunch of lists that have IMO c-grade stuff, like this:
Really not a single really good sounding piece there to me? And some are outright painful. The Shadowfire one is nice actually, but has no percussion, just sounds like an organ piece. Otherwise some good stuff technically, but with much ugliness mixed in.
Paperboy demonstrates really clearly how programmers got around three channels - by using one for both drums and bass, so they have to alternate with clean breaks between both. The Last Ninja has some good uses of the bending to make some nice oriental instrument sounds, but also has heaps of nasty oscillating, and also has another issue common in C64 soundtracks (though not inherent to the chip) - the choice to use extremely high pitched notes. Once again western developers brought the high pitched notes ‘innovation’ to NES a lot when they made games on it too, so it’s not the C64’s fault, just a common issue with its music. The R-type track manages to fake having more channels most successfully by doing the alternating thing very rapidly, but is still warble central and has the high pitched thing too.
In comparison, generally Famicom was simpler but just more pleasant, here’s Konami alone, not even a best of just some random music from each game:
Definitely more homogeneous, but also all sound actually good. And since only one track disappears when playing games, typically it sounds less abrupt - you’d still have drums, bass and either melody or harmony still playing, games would cut either the melody or harmony.
See Contra, which just loses the harmony on the melody, but keeps drums bass and lead, and it can mix the harmony back in smoothly in when there’s no action:
If you wanted music and sound effects, you had two channels left on C64. Often percussion AND harmony got the boot, like in C64 Castlevania
Or R-type which almost skips most sound effects altogether, having them only when it can shove a really flat and short crunch in between notes on one into the ‘faked four channels with three channels’ mix. It’s actually really well done how it managed to do a version of the original arcade tunes with only three channels (but still uses nasty warbles), alternating sound types within single channels, but is so flat sounding on the combat front, you only get sound effects when the melody is taking a break, and then with only wimpy short crunches for shots or hits in most cases
When channels are already serving double duty as 1.5 instrument parts, there’s just no room to slot it sound effects half the time.
Add in expansion audio for FDS and others in Japan, and it just gets nuts with six tracks at once, multiple harmony layers, instrument parts can play and fade at the same time as the next picks up etc
TL:DR Famicom’s instruments were less flexible, but generally nicer sounding, and there were more of them.