Okay, I'll try and write a quick primer
Basically, MIDI provides you with 16 channels. Each channel can have a single instrument assigned to it. You can play as many simultaneous notes on each channel as you like up to the limit of the synth, 32 notes on the D110 by the looks. However, you can only have one different instrument per channel. For example, piano on channel 1, organ on channel 2, bass on channel 3 etc. Channel 10 is reserved for drum sounds.
That's in a perfect world. A Roland JV1010 would do that for example, but in reality many synths will only support one channel (and thus one instrument) at a time. The D110 may or may not do that, I don't know. With (monotimbral) synths like that, you usually get to choose which channel it sits on. My Roland MVS-1 is weird in that it will support several simultaneous instruments (multitimbral) but seems to be fixed to listen on channels 1-5 and nothing else. I also have a Pulse which is a monophonic synthesizer similar to the minimoog - I've configured that to listen on channel 16.
Now, it's possible to use MIDI channels to link two synthesizers together in what is referred to as a daisy-chain. For example, I connect the MVS-1 to the computer, and the Pulse to the MVS-1. If I play on channels 1-5, the MVS will play. If I play on channel 16, the Pulse will play instead.
If I were to attach the JV1010 and have the Pulse piggy-back on it, there would be a problem because both of them are listening on that channel and both synthesizers would play.
The solution to this is to add another MIDI interface, so that you have several, each with its own 16 channels. These might be physically different interfaces, although you often get combined ones like
the MIDISPORT 4x4 which I use. That provides four independent interfaces, so I can put the JV1010 on port 1, and attach the MVS & Pulse to port 2. Port 3 has the Hammond organ, mellotron sampler and Waldorf MicroWave all listening on their own separate channels.
Hopefully that wasn't too much in one go. I think you probably know some of this already since you've got it to the point where it's playing back, albeit with the wrong sounds.
So, I guess the next topic is instrument banks. MIDI provides up to 128 sounds (referred to as 'Programs' or 'Patches'). Most synthesizers have more than this, so they are split into banks. There is some disagreement over how banks are selected - but usually the manual explains this. If I understand the D110 right, there's only one bank anyway.
Anyway. The first thing to do is to make sure the MIDI interface is set up so that Rosegarden sees it, particularly important if you have more than one.
So. Here's a generic shot of rosegarden from my laptop:
https://i89.photobucket.com/albums/k216/tapewolf/scraps/midi/rosegarden1.png
Below the 'segments' menu is a green icon with a keyboard merged into a circuit board. The caption is 'Manage MIDI devices'. If you click on it, you'll get something like this:
https://i89.photobucket.com/albums/k216/tapewolf/scraps/midi/rosegarden3.png
...if yours hasn't been configured already, it's probably got something like 'External device 1', 'External device 2' and so forth. Select one of those, and choose the interface from the dropdown. Since yours seems to be sounding, it's probably okay anyway.
Enter a name like '
Roland D110', make sure the item is highlighted, and click the 'Banks' button.
You should get this:
https://i89.photobucket.com/albums/k216/tapewolf/scraps/midi/rosegarden4.png
If you had an RGD file, you'd highlight the interface you named above ('Roland D110') and click on 'Import' to load it in.
Actually that might be an idea anyway, since it's got a default 'all numbers' program or something you can use as a template.
The interface you selected should have a branch appear beneath it ('Hammond XM-1' in mine), and if you select that (the bank) you should get the patch names appear in the right-hand side. These will probably be just 1,2,3,4 or something. What you can do now is fill in each one with the appropriate sound - there should be a list in the manual, or alternatively I think the D110 has a screen display so you can probably go through them one by one and fill them in. Tedious, but useful. When it's finished (there are tabs at the top to select more pages as it only displays 32 at a time), click 'Export' to save the bank to a new RGD file. Assuming it's all OK, you might want to offer it to
the Rosegarden people for future inclusion.
Here's another example:
https://i89.photobucket.com/albums/k216/tapewolf/scraps/midi/rosegarden5.png
Anyway, when you're done and it's saved, press 'Apply' and close the dialogues until you're back at the main screen.
The next step is to set up each track to have the right instrument.
First click on a track:
https://i89.photobucket.com/albums/k216/tapewolf/scraps/midi/rosegarden1.png
...at the bottom-left corner you can see the bank, program and channel it's assigned to. If you've only got one interface, you can just go through each one, highlighting the track and changing the channel and program. You'll probably find that 'bank' and 'program' are greyed out by default. If you tick the box next to 'bank', you should be able to select your user-defined bank, e.g. 'Roland D110' or whatever. Then you should be able to activate the program dropdown as well, and you'll be able to choose the appropriate program from the list.
Rosegarden also has something of its own which it calls 'Instruments' but I haven't got to the bottom of that yet.
Anyway, you should be able to set the program for each track. Make sure you highlight the track before changing anything - sometimes I forget and end up changing the one I've just set by mistake. Also, make sure each track has its own channel or there will be a fight over which instrument is playing.
If you have several interfaces, highlight the track, right-click and you'll get this:
https://i89.photobucket.com/albums/k216/tapewolf/scraps/midi/rosegarden2.png
The first list is all the interfaces. The second list is all the channels for that interface. You can specify the interface and channel that way, although I think you may also be able to do that from the panel on the left.
...and that should be enough to let you select the instruments. It's quite likely that the D110 simply doesn't support GM, but at least now you should be able to choose suitable alternative instruments easily.
Hope that helps...
Congrats!
