View source for Music Hacking/Tricks of the Trade

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===Music porting===
Ah, yes. Music porting. An infamous practice that many want to achieve. This section will explain the various methods of porting music from one game to another. If something is not possible, it will be noted.

====Sonic 1 -> Sonic 2 Beta====
This is one of the easier jobs in my opinion, but it can be a bit tough at first. The trick is to convert the pointer format from S1 to S2B format. First, you have to convert the header pointers. This is the easiest part, as all the pointers are simple relative pointers. So here's what you do...

First off, mark the location you want to place the music at in pointer form. EX: F8000 goes to 8000, which goes to 0080, etc etc. Then, take this base location and add the relative values to it. So if I was placing my music at F9CDE, and my voice pointer was 0312, I would add 312 bytes to F9CDE. This gives me F9FF0. I then take this and convert it into pointer form. An easy way to do so in this case is to simply remove the F. This leaves me with 9FF0, which I then byteswap. This leaves me with the final converted pointer of F09F. Do this for every pointer in the header, as the rest you can leave intact.

The next job is to convert all the pointers in the coordination flags that have them. There are 3 flags in total that do so: F6, F7, and F8. Become familiar with the syntax; Know which is the pointer and which is not. Converting proceeds as follows...

We'll start with an example of sorts. As I noted before, with coordination flag pointers in S1, signed values are used. FFFF is 0, etc. The math works in the same way as our last job, but this time we use different variables. Our base location is found out by marking the offset of the byte where the actual pointer is. In the case of F6 and F8, the byte after F6/F8. In the case of F7, skip two bytes after the F7 to where the pointer is. This is all in my syntax breakdowns, BTW.

Now that we have our base location, we can convert the pointer. Now remember, instead of 0000 being zero, in this case FFFF is zero. So if we want to convert our pointer easily, we have to make our pointer as simple as the header pointers. For negative jumps (below FFFF), we take the pointer value and subtract it from FFFF. This will leave us with a simple relative value. For example, if my S1 pointer was FFE6, I would subtract FFE6 from FFFF. This gives me 19 as a result, meaning this pointer is meant to locate data 19 bytes before our base location. Now we have to convert this into S2B form. Take your base location and subtract your result relative value (19 in my case) from it. For example, if my base location was FEE90 (90EE), I would subtract 19 bytes from it (my result value from the above operation). That would give me the offset of FEE77. I then convert this into pointer form, giving me the final converted pointer of 77EE.

For positive values (above FFFF), things are a bit simpler. Simply take the positive value and subtract 1 from it. Then, add it to your base location. So if my pointer was 0090, I subtract 1 from it. This gives me 8F. I then add this value to my base location, which was FEE90. FEE90 + 8F = FEF1F. Then, convert this into S2B pointer form. This gives me the final converted pointer of 1FEF. Fun, eh? =P

Remember to do this with ALL pointers in the song. You won't get off correcting two or three, I'll tell you that much. :P

=====Points to note=====
Always remember to change the music pointer to point to your new music. Otherwise you'll have done this all for nothing. Also, S1 voices are not entirely compatible with S2 voices. You may have to apply new voices to the song to make it sound right. This is why the instruments in Esrael's port of Marble zone sounded different; he had to make new ones.

====Porting between Sonic 3K/3D/Crackers/Chaotix====
This job is much simpler, as all pointers use the same format. There are two methods of porting this music between each other...

# Simply put the music in the "same" location according to pointer format. For example, having music at C0000 or C8000 would be the same as having it at 10000 or 18000. All the result pointers would be 0080. Get it? =P Simple copy and paste, and nothing else needs to be done. Just change the music pointer to point to the new music and presto! Ported music. This method limits your customization as where to put the music though, and I don't recommend it unless you are porting whole music banks or it is incredibly convenient. It is easier though, so hey. =P
# Modify all pointers inside the music (header and coordination flags) to go along with the new location you put it at. Here's a simple way to do so...

First off, take your original location, which is the beginning of the song. Then, work out where you are going to put the song. Convert both these values into pointer format. Now, work out the difference between these two values. For example, if the original location was F802A (2A80 in pointer format), and I wanted to put it at FD980 (80D9 in pointer format), then I would subtract my new location from my original location. So in my case, FD980 - F802A. This gives me 5956. Now, this will be your modifying value for each pointer. You add this location to each pointer in the song to get your converted pointer.

Let me give an example of a negative value. My original location was FA000 and my new location was F9027. This time, we switch the operation. FA000 - F9027 = FD9. This time, you subtract this value from each pointer in the song to get the converted pointer. So remember, if you are moving a song to a location before the original location, subtract. If you are moving it to a location beyond the original, add.

=====Points to note=====
If Sonic 3 music has D817 as the voice pointer, then it cannot be ported outside of S3K without being given a new voice set. Sonic 3K is the only game with this universal voice bank, and specifying it in any other game will have no effect.

====Porting from Sonic 2 Beta to Sonic 3K/3D/Crackers/Chaotix====

This is a very simple job, provided you have a good eye for detail. The trick is to replace the differing coordination flags between the two games. This is a simple task, and you can do it in two simple steps.

# Run a search in the song for coordination flag E3. This is the S2 flag to return. We need to replace this with the Sonic 3K/etc equivalent, F9. Change all valid instances of E3 to F9. This will fix awkward jumps in the song that were hindering porting before.

# Run another search in the song for coordination flag E9. This is the S2 flag to add a value to the current channel pitch. We need to replace this with the Sonic 3K equivalent, FB. Change all valid instances of E9 to FB. This will fix certain lagging in some songs, lack of pitch change, and even crashing.

When I mention valid instances, I mean that the values of E9 or E3 are not part of another coordination flag. Make sure you know the format of most coordination flags, as to avoid making fatal mistakes that may destroy your entire port.

=====Points to note=====
Some voices may be wrong. You will have to fix this manually, provided you know how.

====Porting from Sonic 3K/3D/Crackers/Chaotix to Sonic 2 Beta====
Just do the opposite of the method above; replace F9 with E3 and FB with E9.

==References==
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