Incorrect playback of descent12.mid compared to TiMidity++

[iskunk]

FluidSynth version

I verified the issue with a build of the Git tree, commit db86c36b.

$ ./fluidsynth --version
FluidSynth runtime version 2.3.5
Copyright (C) 2000-2024 Peter Hanappe and others.
Distributed under the LGPL license.
SoundFont(R) is a registered trademark of Creative Technology Ltd.

FluidSynth executable version 2.3.5
Sample type=double

Describe the bug

Playback of descent12.mid, a General MIDI file ripped from the old Descent PC game, is incorrect compared to TiMidity++.

Here is a zip file containing the MIDI at issue, and Ogg Vorbis conversions of a portion of the WAV output from TiMidity++ and FluidSynth: fluidsynth-bug-files.zip

At about the 17-second mark, a strong synthetic horn (?) section begins playing. The TiMidity++ rendition sounds correct; it's how I've always heard this piece. FluidSynth, on the other hand, renders it in a most amusingly wrong way.

(If it matters, I used the 8mbgmsfx.sf2 soundfont to render this MIDI file.)

Expected behavior

The horns should sound like the TiMidity++ rendition, not like... that.

Steps to reproduce

These are the commands I used to produce the WAV file outputs. No user config files were present:

$ timidity -x'soundfont 8mbgmsfx.sf2 order=0' -Ow descent12.mid

$ ./fluidsynth -a file -i -n 8mbgmsfx.sf2 descent12.mid

Additional context

I first encountered this bug via the AMIDI-Plug plug-in for the Audacious music player, but quickly tracked it down to the FluidSynth backend.

[derselbst]

Duplicate of #705 (comment) and of #1232

Since this is already the third time someone is running into this, I once again want to emphasize that I'm generally open for changing this or even better, making the range for the portamento time customizable as I've explained here: #705 (comment)

If anybody is willing to invest time for this, pls. create a discussion before filing any PR, as the solution space is quite big.