So here's a question that bugs me: I'm reading that DOSbox does not emulate MIDI hardware, it just passes MIDI info to whatever external synth device you have. And that in Windows there's just one General Midi wavetable. So how come that if I go to sound setup for any DOS game I get a totally different sound on each of the devices listed, including the mythical Roland (which also usually sounds the best). I don't have any synthesizer hardware, it's just me playing a game in DOSbox on Windows with an average onboard soundcard.

Dosbox emulates adlib, so if you use soundblaster or adlib sound (more or less the same), you'll get that OPL3 synthetic sound. General midi will give you the Windows General MIDI, while Roland MT-32 will still use General Midi, only it'll sound a little off.

If you want the best possible sound in your dos games, here's what you do:
1. Download Dosbox ECE Dosbox ECE.
2. Download the Fatboy soundfont.
3. Find the mt-32 ROMs somewhere.
4. Configure games that have general midi to use Fluidsynth with the fatboy soundfont, and configure games that only have MT-32 support to use the MT-32 emulator.

There's only one thing to be said about DOSBox in terms of General MIDI, namely that it does not include any General MIDI emulation whatsoever and relies on external modules to output MIDI music and sounds in this case.

On Windows you're getting the brighter side of the deal, since you're getting basic MIDI support as part of the OS.

The good news in general is that DOSBox can output MIDI to any device/service you want to hook up to it and I think there are plenty of options for MIDI emulation out there.

Unfortunately I've only set it up on Linux, where TiMidity++ serves as a good option. Here is a guide on that, if you ever need to bother with it. DOSBox tutorials are also available on how you can configure it to output MIDI to a certain port on which, in theory, you've already set up a MIDI emulation service.

Edit: Based on teceem's fine point, I have replaced MIDI with General MIDI. Thanks for that :).

Munt is a multi-platform software synthesiser emulating Roland MT-32, CM-32L, CM-64 and LAPC-I.
Both DOSBox and ScummVM support it.
If you have no real MIDI devices, Munt is the best you can get.

Also if you want you can use Roland Sound Canvas https://www.roland.com/global/products/sound_canvas_va/

What is your question exactly?
For old DOS games there are just 4 (or 6) main options (Adlib, MT-32, Gravis Ultrasound and General MIDI compliant cards):
1. Adlib
DOSBox emulation works perfectly fine, nothing can beat it except for native Adlib Gold card.

2. Roland MT-32 (also CM-32L, CM-64 and LAPC-I)
It was the best music option in early nineties, it predates General MIDI that's why they don't mix together well.
DOSBox don't have emulation for that but you can connect real thing into your modern PC and use it.
But the best thing would be to get respective ROMs: MT32_PCM.ROM, MT32_CONTROL.ROM, CM32L_PCM.ROM, CM32L_CONTROL.ROM (they are illegal for distribution unless you make a copy out of your own disc). And then install latest MUNT for near perfect emulation.
https://sourceforge.net/projects/munt/
Please note that this will add additional MIDI device to your PC so you need to change it before you start playing specific MT32 friendly games.

3. Gravis Ultrasound
DOSBox can work with it just fine but you need to get additional files and put them into your DOSBox folder properly. It worked for me, some games like Doom 1 would sound much better than with General MIDI (Roland Sound Canvas).
This will NOT add additional MIDI device, but if we are talking about GOG games then you'll have to tweak separate DOSBox folders respectively and change the music device in setup of course (some GOG games like Wing Commander 1 don't have a way to setup a sound/music card).
Please note that there are very few games designed specifically for Gravis Ultrasound but you might be interested in checking out Ultrawolf, it's modified version of Wolfenstein 3D with support for more sound channels, but they added ugly music for unspecified reasons which I wasn't been able to disable. Adlib music remained intact and it can be disabled, the Gravis music not (perhaps it's possible to get rid of .MOD files)
http://www.pc-freak.net/blog/enable-gravis-ultrasound-dosbox-enhanced-music-experience/
https://archive.org/details/ULTWLF13

4. Roland Sound Canvas
DOSBox don't have music banks for that, but you may buy Sound Canvas VA for only $125 for native Sound Canvas 55, 88 and 88Pro.
https://contentstore.roland.com/software/detail/sound_canvas_va/
Alternatively you may check out freely available custom VA sets, I found one which sound like Sound Canvas 55 for free still I'm planning to buy Sound Canvas VA eventually but it's DRM heavy.
But you can't just use it out of the box, you'll need to install additional software and the best would be loopmidi:
https://www.tobias-erichsen.de/software/loopmidi.html
Please note that this will add additional MIDI device to your PC so you need to change it before you start playing superb full on General MIDI games, some of old games like Dune 2 doesn't list General MIDI in their setup but recognize Sound Canvas.

Here is a link to our fellow GOGer with instructions on how to install it properly.
https://www.youtube.com/watch?v=WumRboSfn90

Also I highly recommend to use Putzlowitschs Vista-MIDIMapper for easy MIDI device change (restart of the MIDI affected program is needed). It works for Vista and Windows 7, and it should work for Windows 10 as well. There are many other free MIDI mappers but this is the most tiny and friendly I've ever tried.
https://putzlowitsch.de/wp-content/uploads/2009/01/plw-vista-midi-mapper_0_93.zip

5. Yamaha S-YXG50 (and later)
It's like Roland Sound Canvas but better, a few games may sound odd in comparison to Sound Canvas.
There are no official VST for this card but you may check what one guy managed to get out of old commercial version:
http://veg.by/ru/projects/syxg50/

6. Turtle Beach
This I will not comment, it is merely an example of MIDI options.

The website says "You'll need internet conectivity to activate this software.", do you happen to know if this means it includes some online DRM or some other form of nastiness?

It's some form of DRM plus a bit of nastiness.

Don't forget, soundcards pre 2000 had really crappy soundfonts for midi that were built in (I think for a keyboard it was like 1Mb of data, while on soundcards it was more like 64k). It was better than nothing....

About the same as 'better than nothing' when using PC Speaker. Audio and early graphics on Dos were atrocious.

I remember using XP and using Timidity++, which basically is a replacement driver for Windows and lets you put in ANY soundfont you want. And the Merlin Soundfont was pretty darn good too. So playing midi files and DosBox games sounded... pretty good.


Heh. I also remember with Windows 95/98 and having a midi output and plugging it into my keyboard and hearing the keyboard PLAY beautiful music vs the crappy built in sound... It was an eye-opener...

ok so from the responses here and some digging I can kind of figure out what's going on:

some people claim that Dosbox does not provide any emulation whatsoever which turns out to NOT be true. Because it does emulate Soundblaster (all Soundblaster settings) and "Soundblaster cards with Adlib support" (AdLib setting)

which is why those settings sound different from any General Midi setting. If you pick any General MIDI then you get the sound of Microsoft GS Wavetable Synth in Windows. And if you pick Mt-32 then you get gibberish.

Roland Sound Canvas is also General MIDI, it turns out, unlike Mt-32, and was the option I picked for most games. It was simply a case of let's see what happens if I pick this option. And what happened was the music sounded different, better. Because it played Microsoft's "bad" synth.

Which all in all means, I guess, that to my ear at least the Microsoft's "bad" synth is still a MUCH BETTER sounding option than Soundblaster or Adlib. People are screwing themselves unaware by playing on Soundblaster unless they consciously want the "authentic" experience of playing back in the day on Soundblaster.

A lot of my early gaming experiences were DOS games on my Soundblaster 16 Card played in Windows 98 DOS-mode or actual DOS, which kind of defined the default MIDI sound in games for me. So it was a shock when I discovered later it could sound different.

Also I have that vague memory of the General Midi option sounding worse than the Roland Sound Canvas option at some point, but I have no idea when, where, on what configuration, and is it even true. I guess I am never gonna get full answers without having the actual PCs and software I used then, whenever it was. Time Machine please!

(a side offtopic question but it came to my mind as I was thinking about all of this - if a game was DOS-only in Windows 98 you got a prompt that you need to restart the PC and if you clicked 'yes' you got auto-booted into DOS and straight into the game? Do I remember that correctly?)

DosBox likely emulates to the same level that VirtualBox and/or WINE emulates. Namely, it puts the appropriate settings to the host OS and then forwards the information, not try to actually make it behave more than necessary. It may use a tiny driver to reply information that it is a piece of hardware there and what it is capable of, but it doesn't include any special functions...

If my x86 memory is correct, the main instruction/opcode you'd use is OUT, which you basically do OUT DX, AL/AX. 200/220 was usually the Adlib/SB port if i remember right.

Original Soundblaster is just an enhanced Adlib.
Both of them are not MIDI devices.

For DOS games that support MIDI, Soundblaster/Adlib is a slightly better fallback option than PC speaker.
But I doubt they really play any MIDI sequences.
You could listen to music and sound using Soundblaster/Adlib, but they are just not MIDI.

how are they not MIDI? both cards had FM synthesizers which took MIDI data relayed by a DOS game and converted it to sound. In every game's soundconfig choosing your card was called "choose MIDI device".

I have no idea what this technical mumbo jumbo means

People often confuse MIDI and General MIDI...

Be more confusing with the 8bit Atari/Apple machines, using the 6502. They didn't have IO ports, they instead reserved portions of memory that were effectively the IO of the system.