I really wanted to make gameboy covers in FT but I'm not sure what the best way to simulate GB sound is.
What I've come up so far:
- Pulse channels work exactly the same on both consoles, no probs here
- The 4-bit wave channels is replaced by one N163 channel
- The 2-bit amplitude of the wave channel is simulated by only using volumes 0,5,10 and 15
- No quick waveform switching as the GB can't handle it.
- The noise channel's highest frequency is very similar to the A-# frequency of the NES noise channel.
The pulse channels actually have a slightly different range (the GB starts at C-1 instead of A-0, and goes slightly higher up too), and only the first pulse channel of the GB can do hardware pitch slides. Also, unless you use a hack, the GB can only do hardware volume envelopes (however the hack does work on a real GB).
Other than that... I suppose your method will get you as close to a real GB sound as the Famicom will allow, though I'm a bit confused as to why you wouldn't use Deflemask instead, which offers you the possibility to make real GB music. I understand that it might not be everyone's cup of tea, but judging from your activity in the Deflemask thread, I believe you're already accustomed to it.
Fun fact: The GB hack to change volume without resetting the wave phase fails on the GBA.
On the GBA, I needed to change the volume on the GB sound channels, so I used timers to perform exactly timed writes so they happened at the same time the wave phase would reset anyway.
