[fluid-dev] Velocity to Initial FC default setting

[S. Christian Collins]

Greetings, fluid-dev group!

I am new here, but I wanted to contribute in any way I can. Sorry, I'm
not a programmer, but I am a long-time SoundFont designer and I have
been exploring FluidSynth lately as part of my foray into Linux. I
believe that FluidSynth is a project of much greater importance than
many realize, especially as Creative seems to be dropping the ball with
their SoundFont support (I won't go into the mess that poses as their
drivers). A good, solid SoundFont synth on Linux will also go a long
way to encourage musicians to dump Windows and use Linux as their music
studio of choice, especially now that major projects such as Ardour are
now adding MIDI support.

I will discuss the "velocity to filter cutoff" modulator, henceforth
referred to as "vel->fc".
In the SoundFont 2.0 spec, you could not modify the default modulators,
and the behavior of vel->fc was as follows:

1. Setting the volume ADSR attack to 0.008 seconds or higher would
automatically apply a filter curve so that lower velocities were
more filtered, with velo=127 being fully unfiltered. This is most
noticeable when the initial filter cutoff is set to a lower value.
2. Setting the volume ADSR attack to 0.006 or higher would not have
the filter curve applied.

For a sound designer, this is annoying--if you wanted a fixed filter
cutoff point with a slow volume attack, then you had to do a hack using
the mod env->fc that I won't go into.

When SoundFont 2.1 came out, designers could now control the modulators
affecting how MIDI events were translated for each patch, including how
the filter was affected by velocity, key, etc. This was a wonderful
development, but Creative's default vel->fc implementation left me
scratching my head. The default vel->fc was implemented using:

1. primary modulator = negative concave curve @ -2400
2. secondary modulator = switch @ -2400

Two questions bothered me. First, why should velocity mess with the
filter unless the SoundFont author expressly specifies such behavior,
and second, why would anyone want a velocity switch as the default
behavior? The switch effectively switches to a tighter filter at
velocity 63 or lower, leaving a jagged bump in the velocity scale. In
all my years of designing SoundFonts, I have never once desired this
behavior.

My solution has been to delete the velo->fc modulator from each patch
that I create (I delete it from the instrument level), and create my own
velo->fc modulator if I need it. However, FluidSynth doesn't seem to
notice that I have deleted the velo->fc modulator and still implements
it, making most of my SoundFonts sound like mush.

I have been able to circumvent the default velo->fc implementation in
FluidSynth by modifying the fluid_mod.c file as follows (section:
'special treatment' for default controller):

* replace this:
if ((mod->src2 == FLUID_MOD_VELOCITY) &&
(mod->src1 == FLUID_MOD_VELOCITY) &&
(mod->flags1 == (FLUID_MOD_GC | FLUID_MOD_UNIPOLAR
| FLUID_MOD_NEGATIVE | FLUID_MOD_LINEAR)) &&
(mod->flags2 == (FLUID_MOD_GC | FLUID_MOD_UNIPOLAR
| FLUID_MOD_POSITIVE | FLUID_MOD_SWITCH)) &&
(mod->dest == GEN_FILTERFC)) {
if (voice->vel < 64){
return (fluid_real_t) mod->amount / 2.0;
} else {
return (fluid_real_t) mod->amount * (127 - voice->vel) / 127;
}
}

* with this:
if ((mod->src2 == FLUID_MOD_VELOCITY) &&
(mod->src1 == FLUID_MOD_VELOCITY) &&
(mod->flags1 == (FLUID_MOD_GC | FLUID_MOD_UNIPOLAR
| FLUID_MOD_NEGATIVE | FLUID_MOD_LINEAR)) &&
(mod->flags2 == (FLUID_MOD_GC | FLUID_MOD_UNIPOLAR
| FLUID_MOD_POSITIVE | FLUID_MOD_SWITCH)) &&
(mod->dest == GEN_FILTERFC)) {
return 0;
}

This is obviously an inelegant hack. However, the vel-fc programming in
my SoundFonts sounds as it should. You can test the SoundFont file for
yourself to see the differences:

http://www.schristiancollins.com/temp/GeneralUser%20GS%20FluidSynth%20v1.41.sf2.bz2

It is my intent to design SoundFonts specifically for FluidSynth in the
future. I believe that this behavior should be modified for future
versions of FluidSynth? It will help many more SoundFonts than just mine.

Thanks,
-~Chris

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