[fluid-dev] An evil screeching noise when playing

[Kimmo Sundqvist]

Hello

This is copy-pasted from my Gentoo bugzilla bug at 

http://bugs.gentoo.org/show_bug.cgi?id=85801

and I'd like to know if any progress has been made with this, or if anyone has 
even heard or experienced this.  The text at the beginning of my first 
bugzilla entry is from this mailing list, so at least the probem is mentioned 
here before.  To me, this makes fluidsynth totally unusable.

From the fluid-dev mailing list
> Recently I got a MIDI interface and a keyboard, and I'm
> trying them out with FluidSynth to render the MIDI. For most
> soundfonts I've tried, the first piano instrument (bank 1,
> program 1) works fine. But when I try almost any other
> instrument and play a few notes, FluidSynth ends up producing
> a horrendously loud noise! The only way I can stop it is by
> changing to a new instrument. It's very weird.

Reproducible: Always
Steps to Reproduce:
1. Emerge fluidsynth 1.0.5
2. Load fluidsynth, load a SoundFont
3. Play a midi file to fluidsynth's port

Actual Results:  
I head the horrible noise very soon after starting the playback.  When the
problem was discussed on the mailing list, they found out that:
a) it has nothing to do with output to ALSA, Jack or file - it happens equally
in every case
b) it has nothing to do with the choice of Soundfonts.  I tried this, and this
was also reported on the mailing list.
c) it has nothing to do with the MIDI file.
d) it appears in 1.0.5 but not in 1.0.3.  Will try this out myself soon.

Later:

Tested 1.0.6 and it is as if nothing has been fixed.  I loaded the Merlin
soundfont and tried playing a midi file.

pmidi blader.mid -p 128:0

It went ok for two seconds, then came the noise.  After about 10 seconds of 
noise, it could produce no output, i.e it was totally silent.  I quitted it, 
reloaded it and the Merlin soundfont.  Tried playing sabre_dance.mid.  It was 
ok for 10 seconds, then I noticed a clicking that got faster and faster, and
suddenly the noise (screech, scream, positive feedback loop, whatever) was 
there again.  It went away after some seconds, and then came back again.  I 
stopped pmidi, and fluidsynth segfaulted.

It is as if fluidsynth was doing some kind of echo or chorus, and had a 
positive feedback loop somewhere, thus resulting in an overload.  Disabling 
chorus and reverb on the cmdline did nothing to help with the feedback, 
though.

Later:

Tried with -O2 instead of -Os, didn't help.  In sabre_dance.mid, the noise 
only seems to happen when a certain instrument is playing.  There is 
something in the midi file that either changes the program for a channel, 
enables or disables chorus or reverb, changes volume or something, that 
starts and stops the screech.

The screech is caused by different instrument or channel in the midi than the
clicking sound.  The clicking sounds like a vinyl turntable skipping a track.

After some playing, it just segfaults.  And in other midi files, the noise, 
once it starts, doesn't stop until I quit fluidsynth, fluidsynth segfaults, 
or the noise dies suddenly.  After the sudden silence there is no sound 
output from fluidsynth at all until I quit or something triggers a segfault.

Later:

I know that typing 'settings' in the fluidsynth console lists all settings.  I
see that I can disable both from the cmdline, by --chorus 0 --reverb 0.  But
typing "chorus 0" or "reverb 0" (or on, off or 1) on the fluidsynth's console
doesn't change the settings displayed by typing "settings."

Typing "set synth.chorus.active whoa" sets it to whoa.  I also tried "toilet"
and "toothfairy" and it didn't complain.  Wonder if it was enabled or disabled
really.

Either the synth really doesn't disable chorus and reverb, or it does, but I
have no way to figure out if it indeed has, and the problem is not related to
reverb and chorus after all.

Fluidsynth also randomly, maybe 50% of the time, crashes on startup with

fluidsynth: fluid_ladspa.c:719: fluid_LADSPA_run: Assertion
`fluid_settings_getint(FxUnit->synth->settings, "synth.effects-channels",
&temp)' failed.
Aborted

I'll try disabling ladcca and recompiling.

Later:

Disabling ladcca in the USE variable didn't help.  Fluidsynth keeps randomly
segfaulting, and after the Sabre dance starts playing, Fluidsynth's CPU usage
slowly (in about 10 seconds, from Gnome system monitor) climbs to 99% and 
stays there.

Before anyone says anything about my hardware, I think I should mention that I
can run memtest86 or The Great Internet Mersenne Prime Search's test for 20
hours with no problems.  I'm leaving this alone now.  If anyone has 
suggestions or 1.0.7 comes out, I'll maybe have a look and try again.

-Kimmo S.