state of advanced audio in Fedora

[Przemek Klosowski]

I was always impressed with the amount and quality of audio software in 
Linux. When it all works, and is driven by someone who knows what 
they're doing, it's essentially a high-end DAW production environment. 
If it all worked smoothly, I am sure it could be one of Linux and Fedora 
showcases.

I am a musical dilettante, so my attempts have been perhaps haphazard, 
but I had a mixed luck: I was able to get everything to run, but the 
setup seemed very brittle. I was not very successful debugging the 
problems because the audio chain is pretty complex, what with the raw 
devices, ALSA, PulseAudio and Jackd having overlapping roles, and lots 
of obsolete and conflicting information on the web. I decided to write 
to the development list in the hope of starting a technical discussion 
that would result in either technical and/or configuration fixes, or at 
least some documentation, that I could perhaps help develop.

I have been using the following programs:

play/aplay      simple .wav players
espeak           speech synthesizer
Qsynth/fluidsynth   .midi players/synthesizers
audacity         sound editor
pianobooster  keyboard play-along teaching tool
Rosegarden w/lilypond music editor
Hydrogen       drum synthesizer
Yoshimi          synthesizer
rakarrack       guitar effect processor

As I said, I was able to use all of them successfully, but I had 
problems integrating them and keeping them up and running in the long 
term. I wonder if I am doing something wrong, or are there technical 
issues that I'm running into, currently on Fedora 25 but also on 
previous versions.

Obviously, out of the box, simple sound obviously works: I can aplay a 
.wav file, espeak works, and some of the synthesizers like audacity and 
hydrogen simply work without any preconditions.
Other audio programs require starting Qsynth first: that seems to be the 
case for Rosegarden, Yoshimi and pianobooster. What is puzzling is that 
there seems to be a lot of hidden state: after running Qsynth for a 
while, the simple sound (aplay, espeak) tend to no longer work: they 
hang without producing any sound, even though Qsynth is no longer 
running. I tried stracing them, but they just go into nanosleep() busy 
loops on internal file descriptors, so it's not clear what exactly 
they're blocking on. I ran into one glitch where qsynth somehow inserted 
a .wav file as a soundfont in the configuration file, which prevented it 
from working subsequently (I had to delete the 
~/.config/rncbc.org/Qsynth.conf file).

I am planning to log some bugzilla reports, but I am not sure against 
what subsystems: is it ALSA, or PulseAudio, or Gnome/pavucontrol, or 
Qsynth. Specifically, I'd like to address the following issues:

- simple sound (aplay, espeak) failing after running fancy synthesized 
sound apps (Qsynth): I'd need guidance what to test to find the hidden 
state that causes that.

- fancy sound apps (Rosegarden/pianobooster) silently failing without 
the synthesizer (Qsynth) running first. I'd like to discuss what could 
be done to at least produce some error messages directing users to set 
up synthesizers first, or maybe to automatically start the required 
synthesizers.