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This tutorial is for how to add a new music song. As an example, we'll add the [Route 47 theme](https://soundcloud.com/mmmmmmmmmmmmmmmmm-1/route-47-gbc-8-bit) demixed from HGSS by [Mmmmmm](https://soundcloud.com/mmmmmmmmmmmmmmmmm-1).
## Contents
1. [Define a music constant](#1-define-a-music-constant)
2. [Create a file for the song](#2-create-a-file-for-the-song)
3. [Update the music pointers](#3-update-the-music-pointers)
4. [Include the new file in the ROM](#4-include-the-new-file-in-the-rom)
## 1. Define a music constant
Edit [constants/music_constants.asm](../blob/master/constants/music_constants.asm):
```diff
; song ids
; Music indexes (see audio/music_pointers.asm)
const_def
const MUSIC_NONE ; 00
...
const MUSIC_MOBILE_CENTER ; 66
+ const MUSIC_ROUTE_47 ; 67
```
## 2. Create a file for the song
Writing your own music is beyond the scope of this tutorial. If you're interested in doing that, start by reading [docs/music_commands.md](../blob/master/docs/music_commands.md) and the source code of existing music. However, there's already a lot of new music available, demixed and remixed from other games by composers like [FroggestSpirit](https://soundcloud.com/froggestspirit), [Mmmmmm](https://soundcloud.com/mmmmmmmmmmmmmmmmm-1), [ShantyTown](https://soundcloud.com/huderlem), and [Pum](https://www.youtube.com/playlist?list=PLQHiVZUO5so0LHdQzx6iu4Ze0zCkbbm7N).
For now, download the [source code](https://pastebin.com/raw/aSDuVfDW) for Mmmmmm's Route 47 theme and save it as **audio/music/route47.asm**:
```diff
+Music_Route47:
+ musicheader 4, 1, Music_Route47_Ch1
+ musicheader 1, 2, Music_Route47_Ch2
+ musicheader 1, 3, Music_Route47_Ch3
+ musicheader 1, 4, Music_Route47_Ch4
+
+Music_Route47_Ch1:
+ ...
+
+Music_Route47_Ch2:
+ ...
+
+Music_Route47_Ch3:
+ ...
+
+Music_Route47_Ch4:
+ ...
```
Notice the label `Music_Route47` before the headers. That's used in the table of music pointers to identify the whole song.
## 3. Update the music pointers
Edit [audio/music_pointers.asm](../blob/master/audio/music_pointers.asm):
```diff
; See song sections in audio.asm.
Music: ; e906e
; entries correspond to MUSIC_* constants
dba Music_Nothing ; 0xe91a3
...
dba Music_PostCredits ; 0xcfd9e
; Crystal adds the following songs:
dba Music_Clair ; 0x1fa8d
...
dba Music_MobileCenter ; 0x17961d
; e91a3
+ dba Music_Route47
```
## 4. Include the new file in the ROM
Edit [audio.asm](../blob/master/audio.asm):
```diff
SECTION "Extra Songs 2", ROMX
INCLUDE "audio/music/postcredits.asm"
+SECTION "New Songs", ROMX
+
+INCLUDE "audio/music/route47.asm"
```
That's it! Now you can use `MUSIC_ROUTE_47` like any other music constant—try assigning it to a map in [data/maps/maps.asm](../blob/master/data/maps/maps.asm).
There is one thing to be aware of if you plan to add a lot of new songs. Crystal's music IDs go from $00, `MUSIC_NONE`, to $66, `MUSIC_MOBILE_CENTER`. If the IDs reach $80 or above they have their high bit set and start getting interpreted differently by `GetMapMusic`. There's a full explanation and fix at the [hard-coded logic](Hard-coded-logic#some-high-values-for-maps-music-ids-play-incorrectly) page.
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