Everything That I Know About Sonic the Hedgehog's Source Code

Slowly chipping away at my source code recreation again. Right now I'm working on the sound driver. While I'd have to wait until I'm entirely done to make a note on all the changes, let's look at the PSG envelopes, and compare the differences between Sonic 1 and Sound Source.
PSG Envelope 3 which is a whistle like sound was lengthened, smoothed, and made a little louder:

Code (Text):

1. Sound Source:
2. EV3    EQU    $
3.     DB    0,0,1,1,3,3,4,5,TBEND
4.  
5. Sonic 1:
6. EV3    EQU    $
7.     DB    0,0,1,1,2,2,3,3,4,4
8.     DB    5,5,6,6,7,7,TBEND

Next, envelope 6. This is a tone that goes down. Strangely you may have noticed that it's data actually comes before 5. This is because in Sound Source, envelope 6 doesn't have an end code, and let's itself go into envelope 5's data, turning it into a lowering and then rising tone. Sonic 1's envelope 6 is also a step quieter and faster.

Code (Text):

1. Sound Source:
2. EV6    EQU    $
3.     DB    4,4,4,4,3,3,3,3,2,2,2,2
4.     DB    1,1,1,1
5. EV5    EQU    $
6.     DB    0,0,0,0,0,0,0,0,0,0
7.     DB    1,1,1,1,1,1,1,1,1,1
8.     DB    1,1,1,1,2,2,2,2,2,2
9.     DB    2,2,3,3,3,3,3,3,3,3
10.     DB    4,TBEND
11.  
12. Sonic 1:
13. EV6    EQU    $
14.     DB    3,3,3,2,2,2,2,1,1,1,0,0,0,0,TBEND

Envelope 7 is entirely different. In Sound Source it's a single step with a value of 2 labelled as a hihat. While in Sonic 1 it's another rising tone.

Code (Text):

1. Sound Source:
2. EV7    EQU    $
3.     DB    2,TBEND            ;HIHAT
4.  
5. Sonic 1:
6. EV7    EQU    $
7.     DB    0,0,0,0,0,0,1,1,1,1,1
8.     DB    2,2,2,2,2,3,3,3,4,4,4
9.     DB    5,5,5,6,7,TBEND

Sonic 1 also has a 9th envelope not present in Sound Source, which plays every value in a rising tone.

Code (Text):

1. EV9    EQU    $
2.     DB    0,1,2,3,4,5,6,7,8,9
3.     DB    AH,BH,CH,DH,EH,FH,TBEND

 

Some stuff that ehw dug up:
- The tool used to create Nemesis compressed data was called "CMM", or "Character Maker MarkV" and was written by Yuji Naka: https://x.com/U1_Toyama/status/1119277351076896769
- There's some usage information for CMM in Tom Payne's papers.

Spoiler: Tom Payne paper scan (56K warning)

 

I've been comparing Sonic CD's Tamabboh 68000 code to the C version's. It looks like the official name of what disassemblies call ObjGetFloorDist is emycol_d. Note that this function is unused in Sonic 3.

 

The unused function in Sonic 3 is something else called CheckFloorDist, emycol_d there is ObjCheckFloorDist and is used a lot. The Sonic 3 disassembly's not really complete, so it's a bit confusing.

 

I'm pretty sure "emycol_d" also shows up in Sonic 2 Nick Arcade, and it's used by the Redz enemy, at least.

 

It's a generic floor collision check for all actors that aren't Sonic. It's present in every game, and is probably one of the oldest subroutines as it was named after the goblin enemy from TTS which would've been the only actor at the time to use it, otherwise it would've been called actcol_d.