1desc: Stereo Widener
 2//width:3<0,6,0.1>Stereo Width
 3//reimplemented from: https://www.musicdsp.org/en/latest/Effects/256-stereo-width-control-obtained-via-transfromation-matrix.html
 4
 5@init
 6width = 2.10;
 7
 8@sample
 9coef_S = width * 0.5;
10
11m = (spl0 + spl1) * 0.5;
12s = (spl1 - spl0) * coef_S;
13
14spl0 = m - s;
15spl1 = m + s;