For me it’s nicer when a string sound don’t stop when I release the key of my master keyboard ; I would like a “natural” stop of this sound, what means that all happens like if I press the key until the sound stops “of himself”, I hope you understand what I mean.
Can someone help me ? Let me know if you need more information.
The sound is 100% determined by the soundfont you loaded into FluidSynth. If you don’t like it, you’ll need a different soundfont, almost certainly. FluidSynth (and SF2 soundfonts in general) do not offer much (any) control over the release duration, it’s built into the soundfont.
You might try increasing the Reverb dry/wet mix setting in FluidSynth. Technically this doesn’t increase the release time of the instrument sound, but it will create a “tail” of sound that might meet your desires/needs.
In general, I have found SF2 soundfonts quite unsatisfactory for realistic performances of acoustic instruments. They rarely sound like the real thing (which is sometimes a good thing, and sometimes not).
Thanks Paul, and I am not sure I have well explained what I need…
Let’s take a sample, a bell sound : if I press a key and keep it, the sound stops after 5 seconds.
I would like that this sound lasts always these 5 seconds, even if I release the key after 2 seconds (so the sound lasts 5 - 2 = 3 seconds without I press any key).
tl;dr: get a different soundfont that sounds the way you want.
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When you create the soundfont (.sf2) file you have to set the release-time (volume envelope) accordingly. In your bell example to 5 sec for the given sample.
Here’s an example for a crash-cymbal (that likewise needs to ring), when editing soundfont in https://www.polyphone-soundfonts.com (env release is set to 100sec):