Strange off-tune portamento #1232
Description
FluidSynth version
FluidSynth runtime version 2.3.2
Copyright (C) 2000-2023 Peter Hanappe and others.
Distributed under the LGPL license.
SoundFont(R) is a registered trademark of Creative Technology Ltd.
FluidSynth executable version 2.3.2
Sample type=float
Describe the bug
When playing Game08.mid from the retro game Descent, track 8 plays a sawtooth wave on channel 5 with portamento. On FluidSynth, the instrument goes strangely off key throughout the sequence. When played with the portamento disabled on channel 5 and when played using an SC-8820 or using BassMidi, the portamento doesn't result in such strange dissonant tones.
Expected behavior
It should be closer to the BassMidi output.
Steps to reproduce
Play Game08.mid. The Fluid R3 soundfont makes it painfully objvious.
Additional context
Recording of what it sounds like with portamento https://drive.google.com/file/d/171h5Rw1DpnDDHqql0ZxPdbltPTiwXbH8/view?usp=share_link
Recording with portamento disabled: https://drive.google.com/file/d/16xmfLkO1HtyTp6qj0f_OYpYfZVSYiLCe/view?usp=share_link
Recording using BassMidi: https://drive.google.com/file/d/170xi-kHXCypR_fYRkUxBGk188b5u6QwI/view?usp=share_link
Original midi with portamento: https://drive.google.com/file/d/17AGZBZGjNNz6FmKspK2Fru1qBi8bosVK/view?usp=share_link