How does one go about making music for Doom WADs?

[HyperVisor]

Hey lol. I make music, and I also enjoy playing doom and making WADs for the game. Well, I'm looking to make my own music for some WADs, but there is like zero information online. I understand the music is basically a converted MIDI file to the MUS format, but like, how does one go about making that midi file with the different instruments? Would you use a tracker, 90s style?

[riderr3]

For changing midi instruments I've using Anvil Studio.

[Scypek2]

And by the way, despite the iwads using music in MUS format, vanilla doom actually supports MIDIs too, so you don't need to worry about converting.

[P41R47]

thats depend of your writing posibilities, in part. If you got a good midi controler, you can use a lot of programs, like Anvil, Sekaiju, Guitar Pro, and others i don't remember right now, to make midis. In fact, every program that had a midi sequencer can be used to write midi music. Reaper is a free one that let you write some MIDI and more.
The other way araound if you don't have a midi controller, is doing it by hand, clicking everything note by note, it takes time, but the other way also takes time, so its depend on what you have or not.
If you are good at writing in pentagram, you can download Sibelius, a sheet editor, that let you save your composition in midi format. Finale is the free choice and it practically works almost the same and have the same save midi function. 
And don't worry abount .MUS. Vanilla Doom can read MIDI files properly.