Re: [fluid-dev] MIDI control change - brightness

[Gerald Pye]

Josh Green wrote:

> I'm not very familiar with this control myself.  What parameter of the
> sound should this actually control?  Brightness doesn't seem that
> descriptive to me, but I have a limited vocabulary when it comes to
> musical terms.  I don't remember seeing this as part of the SoundFont
> standard, which doesn't necessarily mean that it shouldn't be added to
> FluidSynth though.  If you have any more details it might help in
> answering your question better :)

	I think that it's essentially just a low-pass (or treble-cut) filter with a 
variable cut-off frequency. As the cut-off frequency is reduced, so the upper 
harmonics of the sound are increasingly attenuated, thereby making the sound 
seem more 'muffled' - or less 'bright', hence the term 'brightness'.  The 
cut-off frequency is proportional in some way to the 3rd byte of the MIDI 
message, i.e., 0=lowest cut-off frequency (very muffled) and 127=highest cut-off 
frequency (not muffled at all).  I suppose that one could liken its effect to 
the 'tone control' knob that used to appear on those 2-valve record-player 
amplifiers popular in the 1960s!

	In my present application. I'm trying to replicate the effect of sounds coming 
out of a large thick wooden box which has a set of shutters on the front, rather 
like a venetian blind. When the shutters are wide open, the sound obviously 
comes out more freely; as the shutters close more, the sound grows increasingly 
quiet and muffled.

	The intention is to send pairs of control/mode change messages to Fluid to 
achieve this: '176 7 nn' to control channel volume and '176 74 nn' to control 
the brightness (muffled effect). The instigator of the application that 
generates these MIDI messages uses it with Creative soundcards and it apparently 
works with those.

	Hope this helps? I'd hoped that there might be a MIDI spec out there somewhere 
that would define the range of cut-off frequencies available for this function 
but a bit of Googling just now didn't seem to reveal anything specific.

        Cheers,

                Gerald.