I do generate the pulse wave, and the others are exactly the same - I just don't. If you look at the section on pulse wavs, you can see I generate a wave based on register usage, setting 0 or 255 into the dynamic sample.
I found using a sample I recorded of the SID gave a better sound.
I am unsure how you recorded your samples off the SID, but I think part of the reason that it may sound nicer is that SID sound used to be played back using TV speakers using only 4 bits, while playback these days goes straight into quality speakers at 16 bits - which is very shrill for a square/sine/sawtooth wave based chip.
Either way, I was interested because procedural generation of sound is still the real meat of emulation, so this was the part I was hoping you'd cover.
I also don't have RING and high/low/band modulation/filters yet. You'd be surprised how good it is even without them. You do notice on some tunes, but certainly not all them.
Well, you know that those of us who grew up with the real deal will be very anal about getting it just right.
Also, a number of games used some digitized speech or sound playback to mix in with the music, I don't expect the current approach can handle that - and I wonder if GameMaker Studio can handle the timing involved with that, at all.
Would you be able to post a demo (even if only video) of the emulator playing a number of songs, or parts of them? Anything by Rob Hubbard would do as a nice benchmark.