[fluid-dev] FluidSynth velocity to attenuation curve

[S. Christian Collins]

I would like to propose that the FluidSynth velocity-to-attenuation
curve be made more sensitive. I have done a comparison between the
Sound Blaster Audigy's hardware SoundFont synth and FluidSynth and found
that at low velocities, FluidSynth is considerably louder than the
Audigy. I have created a package including actual numbers and a chart
for those interested. The package also includes a SoundFont and MIDI
file for performing your own tests. You can download it here:
http://www.schristiancollins.com/temp/velo_curve_test.tar.gz

The velocity-to-attenuation modulator is set by default to 96 dB. It
can range anywhere from 0 (no velocity curve) to 144 (maximum velocity
curve). On the Audigy, the default 96 dB setting creates quite a
dynamic range between loud and soft, but on FluidSynth there isn't much
variance at all. If I set an instrument to 144 dB velocity curve, it is
better, but FluidSynth's 144 dB setting is still not even as sensitive
as the Audigy's 96 dB! As a result, FluidSynth instruments lack
expressiveness and dynamic range.

In my customized FluidSynth package, I have set the default
velocity-to-attenuation to 144 dB, although this still does not help
instruments that override the default setting. Changing the default to
144 dB isn't a proper fix, but for anyone who wants to know, I changed
line 188 in fluid_synth.c from:

fluid_mod_set_amount(&default_vel2att_mod, 960.0);
to
fluid_mod_set_amount(&default_vel2att_mod, 1440.0);

This is something that should be fixed at a deeper level, though, which
I don't have the know-how to fix.

-~Chris

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