[zeta0134]

Audio is *surprisingly* tricky on both platforms. NES has DPCM, which cheerfully interrupts the CPU and causes untold issues with controller reading. Gameboy has envelopes that are semi-required with phase-resets, and a wave channel which you in theory cannot write new samples to, and developer hacks to work around both. Both systems have various hardware revisions that have subtly different behavior, and a handful of games that will break on that specific model. It's fun!

[gblargg]

It's also more involved to verify operation. Graphics are easier to "measure" and compare. Sound is also much more timing-dependent, e.g. when timers are running on their own all the time. It's disconcerting when sound is slightly off in games.