[sdiy] Programmable Logic?

[Magnus Danielson]

From: James Patchell <patchell at cox.net>
Subject: Re: [sdiy] Programmable Logic?
Date: Mon, 19 Jul 2004 17:55:26 -0700
Message-ID: <5.2.1.1.2.20040719175140.00b718b8 at pop.west.cox.net>

> Actually, this is a subject that kind of fascinates me....although, I have 
> not done much research....
> 
> Doing an ideal tone wheel simulator is easy, in fact, in a spartan 3 it 
> would barely be a hiccup...

I agree, the Spartan 3 is powerfull.

> The problem is the phase jitter...after all, the tone wheel generator is a 
> collection of cogs that do the frequency divisions to get all of the 
> pitches you need, and the gears do not really do a very good job of that, 
> really, however, most people seem to feel (me included), that this is what 
> makes a Hammond organ sound the way it does.  So, the big question is, how 
> do you simulate the non- ideal nature of the tone generator?

If you only want the pitches, then you should be looking at the integer 
relationships of the cogs in the individual gears as well as the number of
wobbles on the tone-wheels themselfs. This should all result in some common
frequency from which you can do divide down. Thus, instead of the traditional
phase-accumulator you end up with something very similar to a TOG. Naturally 
should a power of 2 multiple be used for tonewheel shape waveform playback
(sine with distorsion). If you do the drawbars analogue or digital is a matter
of taste, but it should be fairly easy to do.

So, anyone with the gear-box details at hand that could shift them my way?

Cheers,
Magnus