How do I add midis to my levels?

I'm just wondering how to add custom midis to my levels, I'm working on a Hexen wad and want to add some custom music.
EDIT: Im using Doom Builder, Hexen and Skulltag (Doom in Hexen)

You need a lump management utility program like XWE to insert the midi file into your wad. To get the midi file working once it's in the wad, rename it so it has the same lump name as the music of the level you want to replace. For example, for map01 of Doom II, the music used is named D_RUNNIN in the Iwad.

you may want to use MIDI2MUS in DOS to make sure you're changing its makeup from MIDI to MUS, which is Doom's internal Format. Once this is achieved, you can stick it in the wad. A lot of newer programs convert this for you though, and newer ports care less about the music's format, as they even allow mp3s to be played if renamed to the same extension-less lumps within.

Get XWE
http://youfailit.net/files/xwe116.zip

• Rename the midi to "winnowr.mid" (for it to play on MAP01)
  
• Open your wad with XWE
  
• Double click the Music button on the bottom
  
• Pick the midi file
  
• Close XWE
  

jplstatic said:

you may want to use MIDI2MUS in DOS to make sure you're changing its makeup from MIDI to MUS, which is Doom's internal Format.

That's not exactly true. Vanilla Doom will play MIDI files just fine. Doom95 is the exception, and will only play MUS, making even some vanilla-flavored wads unable to run in it.

Full midi support came with DOS version v1.9.