Doepfer

> This idea sound very similar to the Blacet Improbability Drive. The
> upper and lower limits controlled by the "Width" and the center (the
> level which the random voltage fluctuate around) controlled by "level."
> The module spits out, amongst other things, random voltages btween the
> upper and lower limits as set by the width control. Check out the manual
> for better detail:
>
> http://www.blacet.com/ID.html
>
> THis functionality could be easily achieved with the forthcoming window
> comparator (I think Doepfer announced such a module) and a single random
> voltage generator. Right???
>
> Tony

If I understand everything the Tendency Mask Generator is nothing but a
random voltage source (e.g. A-118) processed by a VCA (that controls the
spread or width) and a unit that adds an offset voltage. In this patch one
has to voltage controlled parameters: width W (VCA) and center C (offset)
and the upper and lower voltages are not controlled directly but by W and C.
But the voltages W and C can be derived from the lower (L) and upper (U)
voltage very simply. The result is:

W = (U-L)/2
C = (U+L)/2

This can be realized very simply by an adder (U+L) and subtractor (U-L)
followed by a 1:2 attenuator. The same circuit is used in the A-137-1 but in
the opposite way (i.e. upper are lower voltage are derived from center and
width, in this case for the upper and lower voltages of the upper and lower
folding level). A low cost quad OpAmp is sufficent for U+L and U-L
calculations.

It would be very easy to develop a module that consists of a VCA, the
adder/subtractor and an offset generator. Such a separate module would have
the advantage that not only a random voltage but any other control voltage
(LFO, ADSR and even audio) could be processed. The module could developed
within less than one day and the price would be in the 50-60 Euro range.

The module could look like this:

Manual Control for U (upper voltage)
CV-Input with attenuator for U (upper voltage)
Manual Control for L (lower voltage)
CV-Input with attenuator for L (lower voltage)
Input
Output

Bakis: how about a poll for such a module (maybe called "Tendency Processor"
?)

Best wishes
Dieter Doepfer



If you are interested in the equations:

U = C+W
L = C-W

calculation of W:

C=U-W
C=L+W

U-W=L+W -> U-L=2W -> W = (U-L)/2

calculation of C:

W = U-C
W = C-L

U-C=C-L -> 2C=U+L -> C = (U+L)/2