Some more ideas on Hammond-Synthesis

[Daniel Oberfeld]

Hi all,
I found that thread quite inspiring, thanx to all contributors!
As I understood it, all tonewheels for one semitone sit one a single axle,
so between equally named semitones of all octaves there should be a quite 
well defined relationship in terms of phase.
On the other hand, this one axle (let's say for semitone F#) is connected to 
the other 11 axles by gear reduction which should lead to an unstable 
relationship in phase-terms due to mechanical tolerances and losses.
So: (quite) constant phase-difference between equally named semitones (e.g. f1#-
f#- F#), floating 
free (or *very* 'soft-synced'???) oscillation of the other semitones in 
relation to our F# (e.g. F#- a).
My solution for simulation of this would be to build twelve analog 
oscillators 
for all 12 semitones C to B of the top octave (no phase lock) and then to divide 
each semitone by quite jitter free dividers to get the other octaves.
If you do it this way you can tune the top octave like a piano to get an 
equally-tempered scale.
By the way : the relationship for a semitone f1 k semitones above a frequency f0 
is:
f1=f0 * ((2) ^ (k/12)). (equally tempered scale, A.Werckmeister)

Juergens second-order PLL idea also seems promising!! Juergen did you already 
find out the bibliographic data of this Funkschau article?? Please let me know.

The crosstalk Bob Schrum put in seems to be quite important, at least the guy 
who tested the Voce V3 for the german keyboards was quite exstatic about it!!

All this leads to the importance of 'irregularities' in the sound of 
instruments. It semms, though, that it should be the musically 'right' 
irregularities. Maybe a discussion from High-Fidelity can be of interest here.
I remember that in the german Stereoplay it was discussed why old FM-tuners 
using variable condensators sounded better than modern (quartz-controlled) 
synthesizer tuners. One idea about that was that synthesizer tuners have a very 
good long-time frequncy-stability but are not as stable as the old condensator 
controlled oscillators when it come to short time stability. Let's say: the 
synth-tuners are instable in the microsecond-domain and stable in the 
millisecond or second -domain, while the condensator tuners are inastable in 
the second- or minute - domain but stable if you look at the microsecond 'time 
window'.
Maybe the human ear doesn't 'like' very short disturbances but finds slower 
irregularities quite interesting!
Another Hifi disussion would confirm that: in the last years the importance of 
the transportation-mechanism for the sound of CD-players was discovered. Like 
in the good old turntable the mechanics seem to influence sound. 
This leads to the topic 'jitter' in the digital signal. Again, its stable if 
you look at it in a minute - time-window but unstable in a micro- or nanosecond 
-time-window.
So, "spring/mass-systems like tonewheels" (as Juergen put it) do certainly 
belong to the 'long time instable, short time stable' group - maybe one should 
avoid all clock controlled principles (belonging to the other group IMHO) when 
trying to simulate a Hammond!!

Was this helpful to anyone??

P.S: Are the divider/harping matrix chips used in the Korg CX-3 (SM 305A and 
SM305B) still available? Any ideas where to get datasheets from? For which 
manufacturer does 'SM' stand for?

OK, I'm out,
Daniel