[Sonic 2/3K] How to use 8-bit PCM for DAC rather than 4-bit DPCM

Have you ever wanted true PCM quality from your drums? This tutorial is for you!
Before you start, you must be aware that this will severely balloon up sample sizes as you're going from 4-bit DPCM to 8-bit PCM so good luck trying to juggle Z80 bank space around (unless you have automatic bank switching).

First, you'll need dpcm2pcm from SMPS Research Pack by ValleyBell to decompress the samples from 4-bit DPCM to 8-bit PCM (or grab them from Sonic 2 Clone Driver v2), then, follow the guide in the spoilers for your specific game.

Spoiler: Sonic 2

First, go into s2.sounddriver.asm.
at zStartDAC, remove this line

Code:

        ld    iy,zDACDecodeTbl

as iy is gonna be unused after these changes.
next at zWriteToDAC, remove these lines

Code:

    rlca
    rlca
    rlca
    rlca
    and    0Fh            ; UPPER 4-bit offset into zDACDecodeTbl
    ld    (.highnybble+2),a    ; store into the instruction after .highnybble (self-modifying code)
    ex    af,af'            ; shadow register 'a' is the 'd' value for 'jman2050' encoding

; zloc_18B
.highnybble:
    add    a,(iy+0)        ; Get byte from zDACDecodeTbl (self-modified to proper index)      

and remove

Code:

        ex    af,af'

as we do not need to be swapping registers since we don't need to be doing decoding anymore.
after

Code:

        ld    (zYM2612_D0),a

next, remove these lines

Code:

        and    0Fh            ; LOWER 4-bit offset into zDACDecodeTbl
    ld    (.lownybble+2),a    ; store into the instruction after .lownybble (self-modifying code)
    ex    af,af'            ; shadow register 'a' is the 'd' value for 'jman2050' encoding

; zloc_1A8
.lownybble:
    add    a,(iy+0)        ; Get byte from zDACDecodeTbl (self-modified to proper index)

and remove

Code:

        ex    af,af'

This change will also make the drums very low pitched from how much code was changed!
If you're using older disassemblies, subtract the pitch values by 10.
If you're using current disassemblies, then change the magic number in dpcmLoopCounter to 179 (since we subtracted 110 cycles total)
Please note that the stock pitches will make the value overflow!

Spoiler: Sonic 3 and Knuckles

First, go to "Sound/Z80 Sound Driver.asm"
at .dac_idle_loop under zPlayDigitalAudio, remove

Code:

        ld    iy, DecTable            ; iy = pointer to jman2050 decode lookup table

at .dac_playback_loop, remove

Code:

        ; Want only the high nibble now, so shift it into position
        rlca
        rlca
        rlca
        rlca
        and    0Fh            ; Get only low nibble (which was the high nibble originally)
        ld    (.sample1_index+2), a    ; Store into following instruction (self-modifying code)
        ld    a, c            ; a = c

.sample1_index:
        add    a, (iy+0)        ; Self-modified code: the index offset is not zero, but what was set above

then remove

Code:

        ld    c, a            ; Set c to the new value of a

also remove

Code:

        and    0Fh            ; Want only the low nibble
        ld    (.sample2_index+2), a    ; Store into following instruction (self-modifying code)
        ld    a, c            ; a = c

;.sample2_index:
        add    a, (iy+0)        ; Self-modified code: the index offset is not zero, but what was set above

and

Code:

        ld    c, a            ; Set c to the new value of a

If you're using current disassemblies, then change the magic number in dpcmLoopCounter to 225 (since we subtracted 72 cycles total)

 

I've had 8-Bit PCM samples in S2 long before this guide existed, lol

I didn't even use clone driver.

EDIT: What I'm about to say here has been resolved


ALSO, if you want the samples already in 8-bit PCM, they are in Clone Driver

 

I mean, the Clone Driver is a 68000 driver, and perhaps someone may want to stick with a Z80 driver? This could still be useful for them.

 

I just meant the PCM files.

 

Other beneficial things to add:

DAC Banks (for Sonic 2):

Clownacy has described how to do it here.
https://forums.sonicretro.org/index.php?threads/making-sonic-2s-sound-driver-good.34124/