Doepfer

I thought I'd describe how do a min/max function and other comparison 
logic using attenuation/offset and the A150 VC switch.

The most simple single-input comparison is to test whether a voltage 
is positive or negative, i.e. X > 0. 

Patch a CV source or other fixed voltage to an A138a mixer channel, 
turn all the mixer knobs fully clockwise, and patch the mixer output 
to the A150's CV input jack. Adjust the CV source until the A150 is 
right at the switching threshold (both LEDs dimly lit).

Now patch your unknown voltage, lets call it X, to a second channel on 
the mixer. If X is positive, the switch will close, and if X is 
negative, the switch will open. That completes the X > 0 patch.

You can use this to create an Absolute Value function:
ABS(X) = if X > 0 then X else -X
Use the voltage inverter module to patch X and -X to the A150's I/O1 
and I/O2 jacks. The O/I output is the Absolute Value function.

You could feed random LFOs or other combined signals to the ABS 
function to get different variations of these signals. Feed the output 
to the A156 if you like, it's always a positive voltage.

To do a two input comparison, or compare two unknown voltages with 
each other, just patch the second voltage Y through the voltage 
inverter to a third channel on the mixer. Now you're testing 
X - Y > 0 which is the same thing as X > Y.

Now you can create the Min and Max functions:
Max(X,Y) = if X > Y then X else Y
Min(X,Y) = if X > Y then Y else X
Just patch the X and Y voltages to the A150's I/O1 and I/O2 jacks. The 
O/I output jack will be the Min or Max function.

There's uses for an X > Y comparison other than the Min/Max functions. 
For example, you could use a sample and hold to compare each 
successive note CV to the previous not, and have different sounds for 
ascending and descending musical passages.

You can also create keyboard zones with a variable split point, 
something digital synths can't usually do. This is useful, for 
example, in a guitar patch, where the transition from wound-string to 
flat-string sounds isn't at a fixed note, like it is on a piano.

To create Dieter's three-input Min/Max function, it's a simple matter 
to cascade two-input Min/Max functions in tandem:
Max(X,Y,Z) = Max(Max(X,Y),Z) (same for Min)

Since the VC Switch and Voltage Inverter are dual modules, all you 
need is a second mixer to create the second Min/Max function.

Give these a try, it'll give you an idea whether the proposed Min/Max 
module will be useful to you. Personally, I would rather have a module 
with just the comparison logic, it would be more versatile. In fact, I 
think it was a big mistake to leave out comparison logic on the A166 
Boolean Logic module, which could have been included instead of those 
stupid placebo jacks on the bottom.

Joe