public override void TouchesBegan (NSSet touches, UIEvent evt)
{
base.TouchesBegan (touches, evt);
var pointOfTouch = ((UITouch)touches.FirstOrDefault ()).LocationInView (this);
pointOfTouch.Y += bottomMargin;
if (graphLayer.Contains (pointOfTouch)) {
touchDown = true;
editPoint = pointOfTouch;
UpdateFrequenciesAndResonance ();
}
}