[sdiy] Silly vector synth question

[Magnus Danielson]

Hi Gordon,

On 06/02/11 01:16, Gordon JC Pearce wrote:
> How does the control law for a vector synth joystick work?
>
> If I have the classic "diamond-shape" joystick with an oscillator at
> each point of the compass, then with the stick centred I should hear all
> four oscillators equally, right?
>
> So if I then move the stick north, south will fade out and north will
> become louder - but with the stick fully north won't I still hear a
> 50/50 mix of east and west?  Does that get "buried" by the increase in
> level of north?

For it to work well, you want the four corners to be that sound only.
Just view it as a square joy-stick turned 45 degrees. Consider it as a 
cross-fade/pan-pot setup. If one of the wipers is X and the other is Y
you can do the cross-fade using the PAN(A,B,X) function (implmeneted as 
you see fit to mix between A and B controlled by X) for form

M1 = PAN(S1,S2,X)
M2 = PAN(S3,S4,X)
O  = PAN(M1,M2,Y)

If X=0 and Y=0 then M1=S1, M2=S3 and output O=M1=S1 (North)
If X=1 and Y=0 then M1=S2, M2=S4 and output O=M1=S2 (East)
If X=0 and Y=1 then M1=S1, M2=S3 and output O=M2=S3 (West)
If X=1 and Y=1 then M1=S2, M2=S4 and output O=M2=S4 (South)

It's best to draw a diamond on a paper and annotate the X and Y values 
as listed above. It takes 3 difference, 3 VCAs and 3 summation setups to 
achieve this. Not too bad.

Sorry if the explanation isn't the most pedagogical one, but hopefully 
you get enough hints to figure it out.

Cheers,
Magnus