04-15-2012, 05:36 PM
I've added tables and code to get the pitch for the tone channels correct. Alas, I suspect that the shift register used for implmenting the noise channel on the T6W28 is 15 bits, and not 16 like on the chips used in the SMS/GG.
Since those basslines you hear in some of the songs are done using the noise channel's "periodic noise" mode (where it outputs a square wave), it'll have the wrong pitch (off by 6.67%) and duty cycle. A C1 would become a C+1/D-1, and a B1 would become something in between B1 and C2, etc.
The duty cycle I can do nothing about, but the pitch could be corrected. The problem is that there's only 4K of RAM for the Z80, and each of these pitch correction tables take up 2K, so I can have one that will make the tone channels sound ok, or one that will make the basslines sound ok, but not both.
Since those basslines you hear in some of the songs are done using the noise channel's "periodic noise" mode (where it outputs a square wave), it'll have the wrong pitch (off by 6.67%) and duty cycle. A C1 would become a C+1/D-1, and a B1 would become something in between B1 and C2, etc.
The duty cycle I can do nothing about, but the pitch could be corrected. The problem is that there's only 4K of RAM for the Z80, and each of these pitch correction tables take up 2K, so I can have one that will make the tone channels sound ok, or one that will make the basslines sound ok, but not both.