I've been playing "Donut Dodo", which is an actually excellent game for Switch I'll be posting more about here later¹, but it solidified for me a slow-building realization over why modern pseudo-retro games often feel just a little bit off to me:
Sound effects in modern 8-bit recreation games don't duck the music channels.
What I mean by this: Old (like, pre-PS2) video game systems had a limited number of sound channels. The NES had five², each hardwired for a particular type of sound, and each channel could only play one sound (one pitch) at a time. You could switch sounds very quickly to try to keep the listener from noticing it, but that was your limitation. "Donut Dodo" is one of many modern games that adopt an aesthetic to appear like they "could have been" on the NES or some other 80s-90s console, and it's more faithful to the limitations of the simulated hardware than many, but the music continues unchanged when a sound effect plays. The music does seem to be fit to NES APU limitations, but it's like there's one sound chip for playing the music and a second for the sound effects.
"Shovel Knight"³ had one of the more thoughtful approaches to voluntary retro limitations I've seen, and wrote a classic longform blog post where they laid out exactly which rules they decided to break and why. Notably, nearly everything they do could have been provided by a sufficiently fancy mapper [expansion chip] in the physical cartridge. But when they explain why they decided not to duck music for SFX they seem to be implicitly outlining an interesting distinction between limitations and flaws; "inauthentic, but much nicer" are their words. People can feel nostalgic for the way NES color-per-tile limitations caused NES environments to be made of large objects each in exactly one shade of monochrome, because that's a limitation that breeds an interesting aesthetic choice, but probably nobody actually enjoyed the way NES sprites flickered when you tried to draw too many on a horizontal line⁴. Yacht Club Games decided SFX-ducking is just something broken.
And yeah, it does suck. But it does have a noticeable aesthetic impact on the music. Music in period console games actually does often show signs of trying to "make room" for sound effects, or at least avoid flourishes that will sound actively bad when sound effects cut them. Very old games occasionally fit their soundtracks into a single channel as if trying to leave the others for sound effects entirely; others use all channels but adopt a particular minimalism that someone who knew they had all channels to themselves might not have. Link to the Past's soundtrack— that's on the Super Nintendo, where all channels were equally-powerful samplers theoretically capable of playing any sound at all, but where there was still a limited channel pool and each channel competed for a shared sample memory— is interesting in that the soundtrack sounds rich and orchestral, but it took me a couple decades to notice that most of the songs contain no percussion, and often are composed from one single sample reused on each channel. When period games didn't leave room for the sound effects you can tell. Consider Secret of Mana, which has a gorgeously lush soundtrack with heavy use of stereo (remember, stereo separation effectively halves your channels). That game had a really bad problem with SFX ducking, with actions as simple as walking up stairs often disconcertingly dropping instruments from the music. Listen to this lategame song from Secret of Mana, and now listen to what happens when the song is played during actual combat; the drums are lost almost completely. Or consider Shantae, one of the last games for the GBC. Shantae was produced late enough that "Chiptune" had by then emerged as a genre distinct from game music; the soundtrack was by Virt, who went on to be a major organizer of the chiptune scene, and the soundtrack sounds like chiptune qua chiptune of the sort composed to be sold on Bandcamp. And Shantae has major problems with SFX ducking swallowing the instruments, listen at 28:50 here or 1:09:30 here.
Donut Dodo has a lush, "modern-sounding" chiptune soundtrack. What does "modern-sounding" mean? It's full of rich sounds and sweepy flourishes. Chiptune composed on a computer-based tracker doesn't have to limit itself to original hardware's channel limitations, and it's not a new observation that this produces a very different sound; we even have examples of that from period hardware, like the Japanese release of Castlevania 3 that uses the VRC6 expansion chip (adds an additional 3 sound channels duplicating the existing 3 waveform channels; expansion chips providing sound was a feature exclusive to the Japanese version of the NES) and consequently sounds "un-NES-like" despite every individual sound being something the NES was capable of and the audio itself being produced by a real Nintendo Famicom. But like I said, I think Donut Dodo is made to original NES APU limitations, and the fact it feels somehow "richer" than ought to be possible comes down, in this case, solely to the fact the composer has the whole chip to themselves and doesn't have to worry about what happens if the player jumps during one of their sweepy tone glides. This isn't actually a problem, I'm sure it's actually the right artistic choice for this game. (And I guess if Donut Dodo were meant to be an actual period game, we could imagine it was created with a VRC6 and just dedicated three of the channels to sound effects. Or, if I'm not listening very carefully and Donut Dodo actually does have a 6-waveform soundtrack, a hypothetical VRC9 chip that adds another 3 on top of that.) But until I put words to what was happening here something just felt off, like a landscape having the wrong number of colors.
¹ (EDIT: See longer writeup here.)
³ Not a game I'm super jazzed on, but the sequel/DLC, "Plague Knight", was great. Plague Knight is so full of interesting ideas and fun mechanical twists it makes the original great by association.
⁴ Though Mega Man 9 actually did have a feature where it would emulate sprite flicker when it detected it was drawing more sprites than an NES could have handled. Hardcore.
Vaguely related, but this reminds me of the lost profession of "sound engineer" or "audio programmer." Nowadays, those sorts of terms are interchangeable with "audio producer" or "foley artist" - they're the people who design/compose the sounds themselves, or maybe they write the software for managing sound (or more likely just wrangling Fmod or Wwise).
In the pre-audio-streaming era, though, "sound engineers" were the ones trying to make audio chips produce the intended sounds at all. Masato Nakamura is credited as the composer for Sonic 1, but he wrote all the music with MIDI (you can actually listen to his original versions here). Two people named Hiroshi Kubota and Yukifumi Makino were credited as "sound program" - they were the ones who actually got these songs to play on the Genesis' YM2612.
This is also why there's certain soundtracks that you "can't believe came from the NES/SNES/whatever." Some people like David Wise and Tim Folin did both the composing and the engineering, so they were playing to the sound chips' capabilities instead of just transcribing MIDI to some other format. Plok's soundtrack typically only uses 5 of the SNES' 8 audio channels, leaving a TON of room for sound effects to play without interrupting anything, and it still sounds closer to CD-quality audio than anything from Yoshi's Island.
