I'm doing a hack of Super Mario Bros. (Lame, I know) and I have no idea where or even how to find where the sound effects are located. I'm using Windhex to edit it and I've already changed all of the music but I want different sound effects, so yeah that's about it. Thanks in advance!

Sound effects are perhaps the least understood element in all of rom hacking.

Relevent link:  SMB Disassembly

After searching it, I think I've found relevent sound effect code/data:


I have no idea where in the ROM this is, but if you search for that string of data at the top (9F 9B 98 96 95 ...) in a hex editor you should be able to find it.

I didn't bother deciphering this to figure out how to change sound effects the way you want -- however you can play around with it in a hex editor to try and tweak things.  Knowing how 6502 and NES sound work would help, but isn't a requirement.  I don't recommend changing any code unless you really know what you're doing, but you should be able to change the constants without messing things up horribly.

To further clarify:  the "constants" are the stuff in data tables (in a ".db" line -- like all that stuff in the SwimStompEnvelopeData table) and/or stuff in a "LD* #$xx" line (line must have a # symbol).

So the first bit of code pasted above:

would look like this in the ROM:


The '40' and '62' would be safe to change.

You have no need to apologize.  You've already shown more initiative than many newbies do.  Nothing wrong with asking questions as long as you're willing to learn, which you seem to demonstrate quite well.  :thumbsup:


These are the opcodes which represent the 6502 instructions.  A good reference page is here:

Obelisk

LDA Immediate mode is represented by opcode A9.  Therefore the line "lda #$40" would be seen as "A9 40" in the ROM.  STA absolute is opcode 9D, therefore "sta $1234" would be seen as "9D 34 12" in the ROM.  And so on.


EDIT:

Since I just realized I only answered part of your question...

It looks like a lot of the sound effects are 'hardcoded' which basically means that the data used in making them is intertwined with the code (all these immediate values -- the ones with the # symbol -- determine how the sound effect will sound, rather than a neat and easy-to-edit table like that SwimStompEnvelopeData table).

If you want to edit these sound effects, it'll be tricky, and you might not be able get it the way you want, but the key is to skim the code and change the immediate values.  You should be able to use the comments and variable names in the disassembly to get some clue as to what the value does.  For example in that code snippit I pasted before:

Here, the immediate (#) value of $28 is being written to Squ1_SfxLenCounter, which indicates that this value determines how long the sound effect is to play.  So you can change that value to make the sound effect shorter/longer.

If you haven't already done so, you really should pick up the disassembly (I linked to it earlier) even if you don't understand 6502.  You can use it to find data tables and other stuff like this in the ROM.

Below the section I pasted is another set of tables labelled 'ExtraLifeFreqData', 'PowerUpGrabFreqData', and 'PUp_VGrow_FreqData' which you might want to look at as well.  Just skim that whole section of the disassembly to look for stuff that's editable.

EDIT AGAIN:

doh you replied before I finished editing!  oh well   :laugh:

You're quite welcome. :-P