Issue: Parameter values on the Envelope/Filter page of Fluidsynth aren't working

[TubularCorpration]

Describe the issue

When an sf2 is loaded into Fluidsynth, all parameters on the Envelope/Filter page are always set to 64, and changing them doesn't affect the sound. the UI graphics respond correctly ((knob graphics move, numerical values change, envelope display changes). Parameters on all other pages work as expected.

To Reproduce

Steps to reproduce the behavior:

1. Add a new instrument chain
2. In the processor selector, choose FluidSynth from the MIDI Instrument/Sampler page
3. When the presets list appears after selecting a MIDI channel, choose any factory installed soundfont
4. Navigate to the Fluidsynth>Envelope/Filter page in the chain controls
5. All parameters on this page are set to their middle value (64). Changing them affects the UI but the sound heard when playing is unchanged.

Expected behaviour

Parameters should reflect actual values in the loaded sf2. Manual changes on this page should produce corresponding changes in the sound.

Actual behaviour

Parameters are always set to 64 and changes made to them only affect the UI display, not the sound produced by FluidSynth itself

Additional context

Almost all of my sampling is done with hardware samplers so I have very little experience with the Soundfont format and may be missing something obvious.

Configuration

Hardware

Raspberry Pi 5 Model B Rev 1.0
Audio: V5 ADAC
Display: MIPI DSI 800x480 (inverted)
Wiring: V5
I2C: MCP23017@0x20, MCP23017@0x21
Profile: v5

System

Debian GNU/Linux 12 (bookworm)
Build Date: 2024-10-02
Memory: 8% (713M/8052M)
SD Card: 6% (26G/470G)
Temperature: 35.6ºC
Overclock: None

MIDI & UI

Tuning: 440 Hz
Master Channel: Off
Preload Presets: On
ZS3 (SubSnapShots): On
Power Save: 10 minutes
Audio Levels on Snapshots: On

Software

zyncoder: oram-2409.2 (36691b3) 
zynthian-ui: oram-2409.4 (dc1a1ca)
zynthian-sys: oram-2409.4 (9cf56bd)
zynthian-data: oram-2409.3 (305b301)
zynthian-webconf: oram-2409.3 (25cda92)

[riban-bw]

Soundfonts may have various parameters enabled in the file. Not all soundfonts have all parameters enabled, e.g. many will not have filters or envelopes. It is a challenge to identify which parameters are available for each soundfont and these may even change between presets in a single soundfont. This makes it difficult to show and appropriate set of controls. Zynthian shows some of the more common controls but they will only operate on soundfonts that are programmed respond to such controls.