[LAU] Connie, an organ template for JACK

[Martin Homuth-Rosemann]

Am Sonntag, 31. Mai 2009 schrieb Fons Adriaensen:
> On Sun, May 31, 2009 at 03:29:42PM +0200, Martin Homuth-Rosemann wrote:
> > I'm just working on this problem. It clicks because I switch the signals
> > on/off without every smoothing at random moments of the sine wave. I've
> > changed the timing to switch at zero crossings and the clicks go away.
>
> Looking at the schematics there is no evidence of any
> 'click removal' action. Also the waveforms summed there
> (for 4',8' and 16') would not be sinewaves. Each divider
> output has an RC lowpass filter before going to the mix
> bus. Assuming the dividers generate square waves, the
> smoothest waveform you can get would be a triangular one.
> What each of these RC filters does exactly will depend on
> the impedance it sees on the mix bus, and this is a complex
> function of the drawbar positions (*all* of them for each
> bus, since they share the resistors) and the number of
> notes already on. If the drawbar for a mix bus is at a
> low setting, or at maximum, its impedance would be quite
> low (the top end is feeding a virtual ground), in that case
> the RC filter frequency moves up, and there is a *highpass*
> action from the series capacitor and the mix bus impedance.
> This impedance reaches a maximum of around 5k for the third
> highest position. If two drawbars are the same position
> their corresponding mix busses are even shorted to each
> other. So just adding the contributions from each note does
> not correspond to what's happening here, both the amplitudes
> and the filtering of each note depend on almost the complete
> state of the instrument.
>
> Ciao,
Ciao Fons,

you're right in your perfectionistic view - this isn't a software simulation 
of the real Continental. Thank you for the dissection of the signal flow - the 
lack of cheap hardware like opamps led to some creative solutions with their 
own special sound.
My first goal wasn't to simulate a specific type of one electronic organ but to 
develop a common toolbox to build an instrument with midi in and jack out. At 
the moment the sound range is from very soft (8' stop only and flute -> sine 
wave) to very harsh (all stops and reed). I'll experiment with triangles and 
square and some kind of "real electronic" waveforms.
The actual version improves i.e. reduces the key click (especially at key 
release). I dont switch the sound on/off at key press/release but ramp it 
up/down for some milliseconds - that's not what a real organ does but it 
sounds better. :)
The vibrato is also a playground - it's a simple mixed fm and am that 
simulates one leslie horn (without crossover) rotating in free field without 
early echoes etc. The "vibrato" drawbar controls the rotating speed (the fm 
modulation strength and the speed of am pan shifting). 
I implemented this effect into the organ because it's easier to do the fm at 
the sound source.

The "gui" is now a bit easier to handle - I switched the keyboard to 
noncanonical and unbuffered. 

Version 0.3.1 (beautiful noise):
http://cryptomys.de/horo/Connie/Connie.tar.gz

Ciao
Martin