[ TL;DR see at the end for some practical suggestions ]
On 29/02/20 18:36, Flavio Sartoretto wrote:
I am running rosegarden on a neat Dell Latitude E7440, under
Ubuntu 18.04.3 LTS \"Bionic Beaver\" - Release amd64 (20190805),
No additional soundcard is available.
Rosegarden works fine.
I should like to load a midi file, then change the instruments.
Beside the "default" engine, associated to FluidR3_GM.sf2 file,
I added 3 engines via qsynth,
PC51f, 2MBGMGS, TimGM6mb,
associated to the corresponding .sf2 files that I found on the WEB.
Not sure what you mean by 'default', but just to be clear, Rosegarden
doesn not provide any 'default' soundfont... I guess you mean that you
loaded the FluidR3_GM.sf2 file in qsynth, whici in turn IIRC some
distributions pull in as a dependency when you install fluidsynth.
I start rosegarden, load a .rg file (let's say Beethoven 5th symphony),
All is OK.
So you did connect via alsa midi (e.g. throgh qjackctl) Rosegarden midi
out to qsynth midi in, right?
Now I activate qsynth. I click on PC51f engine...
Sound does not change...
I click "restart" on qsynth GUI.
I do not understand if fluidsynth is used by rosegarden.
As said above, no not directly. Regarding MIDI and soundfonts Rosegarden
is essentially only able to:
- Send midi via alsa midi (additionally you can create more than one
- 'play' midi through DSSI plugins, including (if it is installed) the
FLuidsynth DSSI plugin.
Indeed jack is involved.
Yes and no... Rosegarden does need jack to run, actually midi is
transmitted via alsa midi. I think qsynth could also work without jack
(like fluidsynth), but I'm not 100% sure.
This is quite confusing because in 99% of cases we (including myself)
are using qjackctl to connect alsa midi as well as jack (or some other
Stopping/resuming jack via qjackctl stops/resumes playing.
But what about fluidsynth?
What about the "connections" in jack?
I guess you mean qjackctl  which is the graphical frontend for jack,
just like qsynth is a graphical frontend for fluidsynth.
There are so many, rather obscure to me...
You are not alone, Linux audio can be a bit confusing, but once you
understand the concepts it's actually quite easy and really flexible :-)
I browsed the web, but I cannot well understand the connections
I don't use qsynth much (I just usually load soundfonts from the
commandline or use Carla  if I'm testing synths), but let's try (and
I might assuming steps you already know, but bear with me):
- In qsynth on the lower left there is a green "+" button, I would
recommend that you add one synth for each soundfont you want to use.
- Then if you open, for instance the, qjackctl's connection tab on
"ALSA" (which is really Alsa midi), under the the writable clients sides
you should now see two or more fluidsynth clients (something like
"128:FLUID ...") for each of the qsynth's you've added
- If Rosegarden is open, on the left side of the same ALSA connection
window under Rosegarden you should have by default "out 1 - General MIDI
device" (the name is actually configurable, but that's the default when
you create a new file).
- Now connect that Rosegarden midi output to the fluidsynth (provided by
qsynth) related to your soundfont, and if you want to change disconnect
one and connect to another.
- As said, in Rosegarden you can also have multiple midi outputs to use
(for instance) multiple SoundFonts check the docs "Devices" 
On caveat of using qsynth is that it needs reloading each time you
change a soundfont. To this end I have found Carla (mentioned above) to
be handier when testing out sounfonts and other synths.
Hope this helps.
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