another jigsaw piece for understanding the Yamaha CS synth magic

[Haible Juergen]

Yamaha CS synth owners might find this interesting:

A few days ago I found another interesting factor that
may contribute to the richness of the sound of Yamaha CS
synths. It's about the voice allocation.

You know I've built that PolyModular interface, and while
at the moment it does nothing more than driving monosynths,
I have these 4 Gate LEDs flashing which represent the
momentarily active voices of the CS-50.

At first glance, I'd call it rotational voice assignment (like
OB-8, as opposed to Prophet 5). Playing single notes
results in 1-2-3-4-1-2 and so on. Holding a note and playing
additional separated notes results in something like 
2 (= held note) + 1-3-4-1-3-4 and so on. Just as it would
be in an OB-8 as well.
But as I kept playing, throwing in 4-voice chords and then
reverting to playing single notes, I suddenly found the
CS-50 allocating *backwards* 1-4-3-2-1-4-3 and so on,
and sometimes even performing more complicated patterns
like 1-3-2-4-1-3-2-4. Now this is not rotational anymore,
but it's still a regular cyclic pattern !

What does this mean for a lively detuning ?

Starting point is the fact that not all voices are tuned exactly identical.
So every note will produce a different beat rate from it's VCOs
(Or on single VCO machines like the CS-50, the beat rate could
result from a previous note that's caught in echo / reverb device.)
Each note has a certain "colour", and the allocation pattern of
these colours has an effect on our perception. 

It's clear that such a regular pattern of slight changes is different
from - and probably more desirable than - "random" detuning
(where you always have too much of it, or not enough). Sucessive
notes played on an OB-8 for instance produce a regular cycle
of 8 differently detuned notes. Which is quite good already.

But apparently the CS synths go one step further. Still creating
regular patterns, these patterns will be changed with every full
hand chord thrown in, but then the same pattern will go on
as long as you play arpeggios.
This is still far from being "random", but even more varied than
the rotational scheme Emu / Oberheim introduced.

I thought this could be interesting for CS synths owners - and
it might help keeping the programmers of VA synths and 
polyphonic Midi-CV interfaces occupied for a while (;->).

JH.