I'm making patches that interface with my Korg and Akai midi controls surfaces and I want to map the knobs (CC 0 - 127) to a slider that goes from -2 to +2.

I usually map the cc to the slider and divide by 127 (to get 0 - 1) but I'm not sure of the formula to map the range from a negative number to positive. Do I use [expr]?
what would the formula be?

-Kai

You first want to get it in the range of 0-4, which you can do by dividing the input by 127/4, or simply 31.75. Then subtract 2 from that.

ah ha, I think a got it...

[hslider]--- [/ 127] ---

• --- [+ 2]

That gives me a range of +2 to -2.
Now to put that in a [expr]

-Kai

Aaah thanks malestorm

I did
[hslider] --- [expr $f1/(127/4)] -- [- 2]
and I got a range of -2 to +2.096 (?) So I used 31.75 as you suggested and that did it.

If I was going to use 127/4, what woulds I wrap that in to get a integer with 2 decimal places?

-Kai

[expr] has a weird quirk in it in that you sometimes have to tell it when to calculate as a float as you would in C (which it is based on). In C if all the numbers are integers, then the output is integer, regardless of whether there should be a fractional part or not. I'm not sure why, but with [expr] parenthesis are treated separately from the rest of the equation (maybe that's also how it is in C?). So the part in parentheses (127/4) gets reduced to 31 instead of 31.75, which is where the 2.096 is coming from. If you change it to 127/4.0, it will work.

An integer with two decimal places? I think that's a paradox.

HAHAHAHAHA yeah I realised what I said after I sent it.

Thanks for the explanation.